.
bunzip2 -c jansson-2.7.tar.bz2 | tar xf - cd jansson-2.7NINDENT NINDENT The source uses GNU Autotools (\%autoconf, \%automake, \%libtool), so compiling and installing is extremely simple: NDENT 0.0 NDENT 3.5
./configure make make check make installNINDENT NINDENT To change the destination directory (/usr/local by default), use the --prefix=DIR argument to ./configure. See ./configure --help for the list of all possible installation options. (There are no options to customize the resulting Jansson binary.) The command make check runs the test suite distributed with Jansson. This step is not strictly necessary, but it may find possible problems that Jansson has on your platform. If any problems are found, please report them. If you obtained the source from a Git repository (or any other source control system), there\(aqs no ./configure script as it\(aqs not kept in version control. To create the script, the build system needs to be bootstrapped. There are many ways to do this, but the easiest one is to use autoreconf: NDENT 0.0 NDENT 3.5
autoreconf -viNINDENT NINDENT This command creates the ./configure script, which can then be used as described above.
bunzip2 -c jansson-2.7.tar.bz2 | tar xf -
cd jansson-2.7
mkdir build
cd build
cmake .. # or ccmake ..() for a GUI.
NINDENT NINDENT Then to build:
NDENT 0.0 NDENT 3.5 make make check make installNINDENT NINDENT
<unpack> cd jansson-2.7 md build cd build cmake -G "Visual Studio 10" ..NINDENT NINDENT You will now have a Visual Studio Solution in your build directory. To run the unit tests build the RUN_TESTS project. If you prefer a GUI the cmake line in the above example can be replaced with: NDENT 0.0 NDENT 3.5
cmake-gui ..NINDENT NINDENT For command line help (including a list of available generators) for \%CMake simply run: NDENT 0.0 NDENT 3.5
cmakeNINDENT NINDENT To list available \%CMake settings (and what they are currently set to) for the project, run: NDENT 0.0 NDENT 3.5
cmake -LH ..NINDENT NINDENT
... cmake -G "Xcode" ..NINDENT NINDENT
... cmake -DJANSSON_BUILD_SHARED_LIBS=1 ..NINDENT NINDENT
... cmake -DCMAKE_INSTALL_PREFIX:PATH=/some/other/path .. make installNINDENT NINDENT
make htmlNINDENT NINDENT and point your browser to doc/_build/html/index.html. \%Sphinx 1.0 or newer is required to generate the documentation.
#include <jansson.h>NINDENT NINDENT in the beginning of every source file that uses Jansson. There\(aqs also just one library to link with, libjansson. Compile and link the program as follows: NDENT 0.0 NDENT 3.5
cc -I/usr/include/jansson -o prog prog.c -ljanssonNINDENT NINDENT Starting from version 1.2, there\(aqs also support for \%pkg-config: NDENT 0.0 NDENT 3.5
cc -o prog prog.c \(gapkg-config --cflags --libs jansson\(gaNINDENT NINDENT
Decoding flags For future needs, a flags parameter was added as the second parameter to all decoding functions, i.e. json_loads(), json_loadf() and json_load_file(). All calls to these functions need to be changed by adding a 0 as the second argument. For example: NDENT 7.0 NDENT 3.5
/* old code */ json_loads(input, &error); /* new code */ json_loads(input, 0, &error);NINDENT NINDENT
Underlying type of JSON integers The underlying C type of JSON integers has been changed from int to the widest available signed integer type, i.e. long long or long, depending on whether long long is supported on your system or not. This makes the whole 64-bit integer range available on most modern systems. jansson.h has a typedef json_int_t to the underlying integer type. int should still be used in most cases when dealing with smallish JSON integers, as the compiler handles implicit type coercion. Only when the full 64-bit range is needed, json_int_t should be explicitly used.
Maximum encoder indentation depth The maximum argument of the JSON_INDENT() macro has been changed from 255 to 31, to free up bits from the flags parameter of json_dumps(), json_dumpf() and json_dump_file(). If your code uses a bigger indentation than 31, it needs to be changed.
Unsigned integers in API functions Version 2.0 unifies unsigned integer usage in the API. All uses of unsigned int and unsigned long have been replaced with size_t. This includes flags, container sizes, etc. This should not require source code changes, as both unsigned int and unsigned long are usually compatible with size_t. NINDENT
gcc -o github_commits github_commits.c -ljansson -lcurlNINDENT NINDENT \%libcurl is used to communicate over the web, so it is required to compile the program. The command line syntax is: NDENT 0.0 NDENT 3.5
github_commits USER REPOSITORYNINDENT NINDENT USER is a GitHub user ID and REPOSITORY is the repository name. Please note that the GitHub API is rate limited, so if you run the program too many times within a short period of time, the sever starts to respond with an error.
[
{
"sha": "<the commit ID>",
"commit": {
"message": "<the commit message>",
<more fields, not important to this tutorial...>
},
<more fields...>
},
{
"sha": "<the commit ID>",
"commit": {
"message": "<the commit message>",
<more fields...>
},
<more fields...>
},
<more commits...>
]
NINDENT NINDENT In our program, the HTTP request is sent using the following
function:
NDENT 0.0 NDENT 3.5 static char *request(const char *url);NINDENT NINDENT It takes the URL as a parameter, preforms a HTTP GET request, and returns a newly allocated string that contains the response body. If the request fails, an error message is printed to stderr and the return value is NULL. For full details, refer to the code, as the actual implementation is not important here.
#include <string.h> #include <jansson.h>NINDENT NINDENT Like all the programs using Jansson, we need to include jansson.h. The following definitions are used to build the GitHub API request URL: NDENT 0.0 NDENT 3.5
#define URL_FORMAT "https://api.github.com/repos/%s/%s/commits" #define URL_SIZE 256NINDENT NINDENT The following function is used when formatting the result to find the first newline in the commit message: NDENT 0.0 NDENT 3.5
/* Return the offset of the first newline in text or the length of
text if there\(aqs no newline */
static int newline_offset(const char *text)
{
const char *newline = strchr(text, \(aq\en\(aq);
if(!newline)
return strlen(text);
else
return (int)(newline - text);
}
NINDENT NINDENT The main function follows. In the beginning, we first declare a bunch
of variables and check the command line parameters:
NDENT 0.0 NDENT 3.5
int main(int argc, char *argv[])
{
size_t i;
char *text;
char url[URL_SIZE];
json_t *root;
json_error_t error;
if(argc != 3)
{
fprintf(stderr, "usage: %s USER REPOSITORY\en\en", argv[0]);
fprintf(stderr, "List commits at USER\(aqs REPOSITORY.\en\en");
return 2;
}
NINDENT NINDENT Then we build the request URL using the user and repository names
given as command line parameters:
NDENT 0.0 NDENT 3.5 snprintf(url, URL_SIZE, URL_FORMAT, argv[1], argv[2]);NINDENT NINDENT This uses the URL_SIZE and URL_FORMAT constants defined above. Now we\(aqre ready to actually request the JSON data over the web: NDENT 0.0 NDENT 3.5
text = request(url); if(!text) return 1;NINDENT NINDENT If an error occurs, our function request prints the error and returns NULL, so it\(aqs enough to just return 1 from the main function. Next we\(aqll call json_loads() to decode the JSON text we got as a response: NDENT 0.0 NDENT 3.5
root = json_loads(text, 0, &error);
free(text);
if(!root)
{
fprintf(stderr, "error: on line %d: %s\en", error.line, error.text);
return 1;
}
NINDENT NINDENT We don\(aqt need the JSON text anymore, so we can free the text
variable right after decoding it. If json_loads() fails, it
returns NULL and sets error information to the json_error_t
structure given as the second parameter. In this case, our program
prints the error information out and returns 1 from the main function.
Now we\(aqre ready to extract the data out of the decoded JSON response.
The structure of the response JSON was explained in section
\%The GitHub Repo Commits API.
We check that the returned value really is an array:
NDENT 0.0 NDENT 3.5
if(!json_is_array(root))
{
fprintf(stderr, "error: root is not an array\en");
json_decref(root);
return 1;
}
NINDENT NINDENT Then we proceed to loop over all the commits in the array:
NDENT 0.0 NDENT 3.5
for(i = 0; i < json_array_size(root); i++)
{
json_t *data, *sha, *commit, *message;
const char *message_text;
data = json_array_get(root, i);
if(!json_is_object(data))
{
fprintf(stderr, "error: commit data %d is not an object\en", i + 1);
json_decref(root);
return 1;
}
...
NINDENT NINDENT The function json_array_size() returns the size of a JSON
array. First, we again declare some variables and then extract the
i\(aqth element of the root array using json_array_get().
We also check that the resulting value is a JSON object.
Next we\(aqll extract the commit ID (a hexadecimal SHA-1 sum),
intermediate commit info object, and the commit message from that
object. We also do proper type checks:
NDENT 0.0 NDENT 3.5
sha = json_object_get(data, "sha");
if(!json_is_string(sha))
{
fprintf(stderr, "error: commit %d: sha is not a string\en", i + 1);
json_decref(root);
return 1;
}
commit = json_object_get(data, "commit");
if(!json_is_object(commit))
{
fprintf(stderr, "error: commit %d: commit is not an object\en", i + 1);
json_decref(root);
return 1;
}
message = json_object_get(commit, "message");
if(!json_is_string(message))
{
fprintf(stderr, "error: commit %d: message is not a string\en", i + 1);
json_decref(root);
return 1;
}
...
NINDENT NINDENT And finally, we\(aqll print the first 8 characters of the commit ID and
the first line of the commit message. A C-style string is extracted
from a JSON string using json_string_value():
NDENT 0.0 NDENT 3.5
message_text = json_string_value(message);
printf("%.8s %.*s\en",
json_string_value(id),
newline_offset(message_text),
message_text);
}
NINDENT NINDENT After sending the HTTP request, we decoded the JSON text using
json_loads(), remember? It returns a new reference to the
JSON value it decodes. When we\(aqre finished with the value, we\(aqll need
to decrease the reference count using json_decref(). This way
Jansson can release the resources:
NDENT 0.0 NDENT 3.5 json_decref(root); return 0;NINDENT NINDENT For a detailed explanation of reference counting in Jansson, see apiref-reference-count in apiref. The program\(aqs ready, let\(aqs test it and view the latest commits in Jansson\(aqs repository: NDENT 0.0 NDENT 3.5
$ ./github_commits akheron jansson 1581f26a Merge branch \(aq2.3\(aq aabfd493 load: Change buffer_pos to be a size_t bd72efbd load: Avoid unexpected behaviour in macro expansion e8fd3e30 Document and tweak json_load_callback() 873eddaf Merge pull request #60 from rogerz/contrib bd2c0c73 Ignore the binary test_load_callback 17a51a4b Merge branch \(aq2.3\(aq 09c39adc Add json_load_callback to the list of exported symbols cbb80baf Merge pull request #57 from rogerz/contrib 040bd7b0 Add json_load_callback() 2637faa4 Make test stripping locale independent <...>NINDENT NINDENT
#include <jansson.h>NINDENT NINDENT in each source file. All constants are prefixed with JSON_ (except for those describing the library version, prefixed with JANSSON_). Other identifiers are prefixed with json_. Type names are suffixed with _t and typedef\(aqd so that the struct keyword need not be used.
JANSSON_MAJOR_VERSION, JANSSON_MINOR_VERSION, JANSSON_MICRO_VERSION Integers specifying the major, minor and micro versions, respectively.
JANSSON_VERSION A string representation of the current version, e.g. "1.2.1" or "1.3".
JANSSON_VERSION_HEX A 3-byte hexadecimal representation of the version, e.g. 0x010201 for version 1.2.1 and 0x010300 for version 1.3. This is useful in numeric comparisions, e.g.: NDENT 7.0 NDENT 3.5
#if JANSSON_VERSION_HEX >= 0x010300 /* Code specific to version 1.3 and above */ #endifNINDENT NINDENT NINDENT
json_t This data structure is used throughout the library to represent all JSON values. It always contains the type of the JSON value it holds and the value\(aqs reference count. The rest depends on the type of the value. NINDENT Objects of json_t are always used through a pointer. There are APIs for querying the type, manipulating the reference count, and for constructing and manipulating values of different types. Unless noted otherwise, all API functions return an error value if an error occurs. Depending on the function\(aqs signature, the error value is either NULL or -1. Invalid arguments or invalid input are apparent sources for errors. Memory allocation and I/O operations may also cause errors.
enum json_type The type of a JSON value. The following members are defined:
| JSON_OBJECT |
| JSON_ARRAY |
| JSON_STRING |
| JSON_INTEGER |
| JSON_REAL |
| JSON_TRUE |
| JSON_FALSE |
| JSON_NULL |
int json_typeof(const json_t *json) Return the type of the JSON value (a json_type cast to int). json MUST NOT be NULL. This function is actually implemented as a macro for speed. NINDENT NDENT 0.0
json_is_object(const json_t *json)
json_is_array(const json_t *json)
json_is_string(const json_t *json)
json_is_integer(const json_t *json)
json_is_real(const json_t *json)
json_is_true(const json_t *json)
json_is_false(const json_t *json)
json_is_null(const json_t *json) These functions (actually macros) return true (non-zero) for values of the given type, and false (zero) for values of other types and for NULL. NINDENT NDENT 0.0
json_is_number(const json_t *json) Returns true for values of types JSON_INTEGER and JSON_REAL, and false for other types and for NULL. NINDENT NDENT 0.0
json_is_boolean(const json_t *json) Returns true for types JSON_TRUE and JSON_FALSE, and false for values of other types and for NULL. NINDENT NDENT 0.0
json_boolean_value(const json_t *json) Alias of json_is_true(), i.e. returns 1 for JSON_TRUE and 0 otherwise. New in version 2.7. NINDENT
json_t *json_incref(json_t *json) Increment the reference count of json if it\(aqs not NULL. Returns json. NINDENT NDENT 0.0
void json_decref(json_t *json) Decrement the reference count of json. As soon as a call to json_decref() drops the reference count to zero, the value is destroyed and it can no longer be used. NINDENT Functions creating new JSON values set the reference count to 1. These functions are said to return a new reference. Other functions returning (existing) JSON values do not normally increase the reference count. These functions are said to return a borrowed reference. So, if the user will hold a reference to a value returned as a borrowed reference, he must call json_incref(). As soon as the value is no longer needed, json_decref() should be called to release the reference. Normally, all functions accepting a JSON value as an argument will manage the reference, i.e. increase and decrease the reference count as needed. However, some functions steal the reference, i.e. they have the same result as if the user called json_decref() on the argument right after calling the function. These functions are suffixed with _new or have _new_ somewhere in their name. For example, the following code creates a new JSON array and appends an integer to it: NDENT 0.0 NDENT 3.5
json_t *array, *integer; array = json_array(); integer = json_integer(42); json_array_append(array, integer); json_decref(integer);NINDENT NINDENT Note how the caller has to release the reference to the integer value by calling json_decref(). By using a reference stealing function json_array_append_new() instead of json_array_append(), the code becomes much simpler: NDENT 0.0 NDENT 3.5
json_t *array = json_array(); json_array_append_new(array, json_integer(42));NINDENT NINDENT In this case, the user doesn\(aqt have to explicitly release the reference to the integer value, as json_array_append_new() steals the reference when appending the value to the array. In the following sections it is clearly documented whether a function will return a new or borrowed reference or steal a reference to its argument.
json_t *obj = json_object(); json_object_set(obj, "foo", obj);NINDENT NINDENT Jansson will refuse to do this, and json_object_set() (and all the other such functions for objects and arrays) will return with an error status. The indirect case is the dangerous one: NDENT 0.0 NDENT 3.5
json_t *arr1 = json_array(), *arr2 = json_array(); json_array_append(arr1, arr2); json_array_append(arr2, arr1);NINDENT NINDENT In this example, the array arr2 is contained in the array arr1, and vice versa. Jansson cannot check for this kind of indirect circular references without a performance hit, so it\(aqs up to the user to avoid them. If a circular reference is created, the memory consumed by the values cannot be freed by json_decref(). The reference counts never drops to zero because the values are keeping the references to each other. Moreover, trying to encode the values with any of the encoding functions will fail. The encoder detects circular references and returns an error status.
json_t *json_true(void) Return value: New reference. Returns the JSON true value. NINDENT NDENT 0.0
json_t *json_false(void) Return value: New reference. Returns the JSON false value. NINDENT NDENT 0.0
json_t *json_boolean(val) Return value: New reference. Returns JSON false if val is zero, and JSON true otherwise. This is a macro, and equivalent to val ? json_true() : json_false(). New in version 2.4. NINDENT NDENT 0.0
json_t *json_null(void) Return value: New reference. Returns the JSON null value. NINDENT
json_t *json_string(const char *value) Return value: New reference. Returns a new JSON string, or NULL on error. value must be a valid null terminated UTF-8 encoded Unicode string. NINDENT NDENT 0.0
json_t *json_stringn(const char *value, size_t len) Return value: New reference. Like json_string(), but with explicit length, so value may contain null characters or not be null terminated. NINDENT NDENT 0.0
json_t *json_string_nocheck(const char *value) Return value: New reference. Like json_string(), but doesn\(aqt check that value is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means). NINDENT NDENT 0.0
json_t *json_stringn_nocheck(const char *value, size_t len) Return value: New reference. Like json_string_nocheck(), but with explicit length, so value may contain null characters or not be null terminated. NINDENT NDENT 0.0
const char *json_string_value(const json_t *string) Returns the associated value of string as a null terminated UTF-8 encoded string, or NULL if string is not a JSON string. The retuned value is read-only and must not be modified or freed by the user. It is valid as long as string exists, i.e. as long as its reference count has not dropped to zero. NINDENT NDENT 0.0
size_t json_string_length(const json_t *string) Returns the length of string in its UTF-8 presentation, or zero if string is not a JSON string. NINDENT NDENT 0.0
int json_string_set(const json_t *string, const char *value) Sets the associated value of string to value. value must be a valid UTF-8 encoded Unicode string. Returns 0 on success and -1 on error. NINDENT NDENT 0.0
int json_string_setn(json_t *string, const char *value, size_t len) Like json_string_set(), but with explicit length, so value may contain null characters or not be null terminated. NINDENT NDENT 0.0
int json_string_set_nocheck(const json_t *string, const char *value) Like json_string_set(), but doesn\(aqt check that value is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means). NINDENT NDENT 0.0
int json_string_setn_nocheck(json_t *string, const char *value, size_t len) Like json_string_set_nocheck(), but with explicit length, so value may contain null characters or not be null terminated. NINDENT
json_int_t This is the C type that is used to store JSON integer values. It represents the widest integer type available on your system. In practice it\(aqs just a typedef of long long if your compiler supports it, otherwise long. Usually, you can safely use plain int in place of json_int_t, and the implicit C integer conversion handles the rest. Only when you know that you need the full 64-bit range, you should use json_int_t explicitly. NINDENT NDENT 0.0
JSON_INTEGER_IS_LONG_LONG This is a preprocessor variable that holds the value 1 if json_int_t is long long, and 0 if it\(aqs long. It can be used as follows: NDENT 7.0 NDENT 3.5
#if JSON_INTEGER_IS_LONG_LONG /* Code specific for long long */ #else /* Code specific for long */ #endifNINDENT NINDENT
JSON_INTEGER_FORMAT This is a macro that expands to a printf() conversion specifier that corresponds to json_int_t, without the leading % sign, i.e. either "lld" or "ld". This macro is required because the actual type of json_int_t can be either long or long long, and printf() reuiqres different length modifiers for the two. Example: NDENT 7.0 NDENT 3.5
json_int_t x = 123123123;
printf("x is %" JSON_INTEGER_FORMAT "\en", x);
NINDENT NINDENT NINDENT NDENT 0.0 json_t *json_integer(json_int_t value) Return value: New reference. Returns a new JSON integer, or NULL on error. NINDENT NDENT 0.0
json_int_t json_integer_value(const json_t *integer) Returns the associated value of integer, or 0 if json is not a JSON integer. NINDENT NDENT 0.0
int json_integer_set(const json_t *integer, json_int_t value) Sets the associated value of integer to value. Returns 0 on success and -1 if integer is not a JSON integer. NINDENT NDENT 0.0
json_t *json_real(double value) Return value: New reference. Returns a new JSON real, or NULL on error. NINDENT NDENT 0.0
double json_real_value(const json_t *real) Returns the associated value of real, or 0.0 if real is not a JSON real. NINDENT NDENT 0.0
int json_real_set(const json_t *real, double value) Sets the associated value of real to value. Returns 0 on success and -1 if real is not a JSON real. NINDENT In addition to the functions above, there\(aqs a common query function for integers and reals: NDENT 0.0
double json_number_value(const json_t *json) Returns the associated value of the JSON integer or JSON real json, cast to double regardless of the actual type. If json is neither JSON real nor JSON integer, 0.0 is returned. NINDENT
json_t *json_array(void) Return value: New reference. Returns a new JSON array, or NULL on error. Initially, the array is empty. NINDENT NDENT 0.0
size_t json_array_size(const json_t *array) Returns the number of elements in array, or 0 if array is NULL or not a JSON array. NINDENT NDENT 0.0
json_t *json_array_get(const json_t *array, size_t index) Return value: Borrowed reference. Returns the element in array at position index. The valid range for index is from 0 to the return value of json_array_size() minus 1. If array is not a JSON array, if array is NULL, or if index is out of range, NULL is returned. NINDENT NDENT 0.0
int json_array_set(json_t *array, size_t index, json_t *value) Replaces the element in array at position index with value. The valid range for index is from 0 to the return value of json_array_size() minus 1. Returns 0 on success and -1 on error. NINDENT NDENT 0.0
int json_array_set_new(json_t *array, size_t index, json_t *value) Like json_array_set() but steals the reference to value. This is useful when value is newly created and not used after the call. NINDENT NDENT 0.0
int json_array_append(json_t *array, json_t *value) Appends value to the end of array, growing the size of array by 1. Returns 0 on success and -1 on error. NINDENT NDENT 0.0
int json_array_append_new(json_t *array, json_t *value) Like json_array_append() but steals the reference to value. This is useful when value is newly created and not used after the call. NINDENT NDENT 0.0
int json_array_insert(json_t *array, size_t index, json_t *value) Inserts value to array at position index, shifting the elements at index and after it one position towards the end of the array. Returns 0 on success and -1 on error. NINDENT NDENT 0.0
int json_array_insert_new(json_t *array, size_t index, json_t *value) Like json_array_insert() but steals the reference to value. This is useful when value is newly created and not used after the call. NINDENT NDENT 0.0
int json_array_remove(json_t *array, size_t index) Removes the element in array at position index, shifting the elements after index one position towards the start of the array. Returns 0 on success and -1 on error. The reference count of the removed value is decremented. NINDENT NDENT 0.0
int json_array_clear(json_t *array) Removes all elements from array. Returns 0 on sucess and -1 on error. The reference count of all removed values are decremented. NINDENT NDENT 0.0
int json_array_extend(json_t *array, json_t *other_array) Appends all elements in other_array to the end of array. Returns 0 on success and -1 on error. NINDENT The following macro can be used to iterate through all elements in an array. NDENT 0.0
json_array_foreach(array, index, value) Iterate over every element of array, running the block of code that follows each time with the proper values set to variables index and value, of types size_t and json_t * respectively. Example: NDENT 7.0 NDENT 3.5
/* array is a JSON array */
size_t index;
json_t *value;
json_array_foreach(array, index, value) {
/* block of code that uses index and value */
}
NINDENT NINDENT The items are returned in increasing index order.
This macro expands to an ordinary for statement upon
preprocessing, so its performance is equivalent to that of
hand-written code using the array access functions.
The main advantage of this macro is that it abstracts
away the complexity, and makes for shorter, more
concise code.
New in version 2.5.
NINDENT json_t *json_object(void) Return value: New reference. Returns a new JSON object, or NULL on error. Initially, the object is empty. NINDENT NDENT 0.0
size_t json_object_size(const json_t *object) Returns the number of elements in object, or 0 if object is not a JSON object. NINDENT NDENT 0.0
json_t *json_object_get(const json_t *object, const char *key) Return value: Borrowed reference. Get a value corresponding to key from object. Returns NULL if key is not found and on error. NINDENT NDENT 0.0
int json_object_set(json_t *object, const char *key, json_t *value) Set the value of key to value in object. key must be a valid null terminated UTF-8 encoded Unicode string. If there already is a value for key, it is replaced by the new value. Returns 0 on success and -1 on error. NINDENT NDENT 0.0
int json_object_set_nocheck(json_t *object, const char *key, json_t *value) Like json_object_set(), but doesn\(aqt check that key is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means). NINDENT NDENT 0.0
int json_object_set_new(json_t *object, const char *key, json_t *value) Like json_object_set() but steals the reference to value. This is useful when value is newly created and not used after the call. NINDENT NDENT 0.0
int json_object_set_new_nocheck(json_t *object, const char *key, json_t *value) Like json_object_set_new(), but doesn\(aqt check that key is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means). NINDENT NDENT 0.0
int json_object_del(json_t *object, const char *key) Delete key from object if it exists. Returns 0 on success, or -1 if key was not found. The reference count of the removed value is decremented. NINDENT NDENT 0.0
int json_object_clear(json_t *object) Remove all elements from object. Returns 0 on success and -1 if object is not a JSON object. The reference count of all removed values are decremented. NINDENT NDENT 0.0
int json_object_update(json_t *object, json_t *other) Update object with the key-value pairs from other, overwriting existing keys. Returns 0 on success or -1 on error. NINDENT NDENT 0.0
int json_object_update_existing(json_t *object, json_t *other) Like json_object_update(), but only the values of existing keys are updated. No new keys are created. Returns 0 on success or -1 on error. New in version 2.3. NINDENT NDENT 0.0
int json_object_update_missing(json_t *object, json_t *other) Like json_object_update(), but only new keys are created. The value of any existing key is not changed. Returns 0 on success or -1 on error. New in version 2.3. NINDENT The following macro can be used to iterate through all key-value pairs in an object. NDENT 0.0
json_object_foreach(object, key, value) Iterate over every key-value pair of object, running the block of code that follows each time with the proper values set to variables key and value, of types const char * and json_t * respectively. Example: NDENT 7.0 NDENT 3.5
/* obj is a JSON object */
const char *key;
json_t *value;
json_object_foreach(obj, key, value) {
/* block of code that uses key and value */
}
NINDENT NINDENT The items are not returned in any particular order.
This macro expands to an ordinary for statement upon
preprocessing, so its performance is equivalent to that of
hand-written iteration code using the object iteration protocol
(see below). The main advantage of this macro is that it abstracts
away the complexity behind iteration, and makes for shorter, more
concise code.
New in version 2.3.
NINDENT The following functions implement an iteration protocol for objects,
allowing to iterate through all key-value pairs in an object. The
items are not returned in any particular order, as this would require
sorting due to the internal hashtable implementation.
NDENT 0.0 void *json_object_iter(json_t *object) Returns an opaque iterator which can be used to iterate over all key-value pairs in object, or NULL if object is empty. NINDENT NDENT 0.0
void *json_object_iter_at(json_t *object, const char *key) Like json_object_iter(), but returns an iterator to the key-value pair in object whose key is equal to key, or NULL if key is not found in object. Iterating forward to the end of object only yields all key-value pairs of the object if key happens to be the first key in the underlying hash table. NINDENT NDENT 0.0
void *json_object_iter_next(json_t *object, void *iter) Returns an iterator pointing to the next key-value pair in object after iter, or NULL if the whole object has been iterated through. NINDENT NDENT 0.0
const char *json_object_iter_key(void *iter) Extract the associated key from iter. NINDENT NDENT 0.0
json_t *json_object_iter_value(void *iter) Return value: Borrowed reference. Extract the associated value from iter. NINDENT NDENT 0.0
int json_object_iter_set(json_t *object, void *iter, json_t *value) Set the value of the key-value pair in object, that is pointed to by iter, to value. NINDENT NDENT 0.0
int json_object_iter_set_new(json_t *object, void *iter, json_t *value) Like json_object_iter_set(), but steals the reference to value. This is useful when value is newly created and not used after the call. NINDENT NDENT 0.0
void *json_object_key_to_iter(const char *key) Like json_object_iter_at(), but much faster. Only works for values returned by json_object_iter_key(). Using other keys will lead to segfaults. This function is used internally to implement json_object_foreach(). New in version 2.3. NINDENT The iteration protocol can be used for example as follows: NDENT 0.0 NDENT 3.5
/* obj is a JSON object */
const char *key;
json_t *value;
void *iter = json_object_iter(obj);
while(iter)
{
key = json_object_iter_key(iter);
value = json_object_iter_value(iter);
/* use key and value ... */
iter = json_object_iter_next(obj, iter);
}
NINDENT NINDENT NDENT 0.0 void json_object_seed(size_t seed) Seed the hash function used in Jansson\(aqs hashtable implementation. The seed is used to randomize the hash function so that an attacker cannot control its output. If seed is 0, Jansson generates the seed itselfy by reading random data from the operating system\(aqs entropy sources. If no entropy sources are available, falls back to using a combination of the current timestamp (with microsecond precision if possible) and the process ID. If called at all, this function must be called before any calls to json_object(), either explicit or implicit. If this function is not called by the user, the first call to json_object() (either explicit or implicit) seeds the hash function. See portability-thread-safety for notes on thread safety. If repeatable results are required, for e.g. unit tests, the hash function can be "unrandomized" by calling json_object_seed() with a constant value on program startup, e.g. json_object_seed(1). New in version 2.6. NINDENT
json_error_t NDENT 7.0
char text[] The error message (in UTF-8), or an empty string if a message is not available. NINDENT NDENT 7.0
char source[] Source of the error. This can be (a part of) the file name or a special identifier in angle brackers (e.g. <string>). NINDENT NDENT 7.0
int line The line number on which the error occurred. NINDENT NDENT 7.0
int column The column on which the error occurred. Note that this is the character column, not the byte column, i.e. a multibyte UTF-8 character counts as one column. NINDENT NDENT 7.0
size_t position The position in bytes from the start of the input. This is useful for debugging Unicode encoding problems. NINDENT NINDENT The normal use of json_error_t is to allocate it on the stack, and pass a pointer to a function. Example: NDENT 0.0 NDENT 3.5
int main() {
json_t *json;
json_error_t error;
json = json_load_file("/path/to/file.json", 0, &error);
if(!json) {
/* the error variable contains error information */
}
...
}
NINDENT NINDENT Also note that if the call succeeded (json != NULL in the above
example), the contents of error are generally left unspecified.
The decoding functions write to the position member also on
success. See apiref-decoding for more info.
All functions also accept NULL as the json_error_t pointer,
in which case no error information is returned to the caller.
JSON_INDENT(n) Pretty-print the result, using newlines between array and object items, and indenting with n spaces. The valid range for n is between 0 and 31 (inclusive), other values result in an undefined output. If JSON_INDENT is not used or n is 0, no newlines are inserted between array and object items. The JSON_MAX_INDENT constant defines the maximum indentation that can be used, and its value is 31. Changed in version 2.7: Added JSON_MAX_INDENT.
JSON_COMPACT This flag enables a compact representation, i.e. sets the separator between array and object items to "," and between object keys and values to ":". Without this flag, the corresponding separators are ", " and ": " for more readable output.
JSON_ENSURE_ASCII If this flag is used, the output is guaranteed to consist only of ASCII characters. This is achived by escaping all Unicode characters outside the ASCII range.
JSON_SORT_KEYS If this flag is used, all the objects in output are sorted by key. This is useful e.g. if two JSON texts are diffed or visually compared.
JSON_PRESERVE_ORDER If this flag is used, object keys in the output are sorted into the same order in which they were first inserted to the object. For example, decoding a JSON text and then encoding with this flag preserves the order of object keys.
JSON_ENCODE_ANY Specifying this flag makes it possible to encode any JSON value on its own. Without it, only objects and arrays can be passed as the root value to the encoding functions. Note: Encoding any value may be useful in some scenarios, but it\(aqs generally discouraged as it violates strict compatiblity with \%RFC 4627. If you use this flag, don\(aqt expect interoperatibility with other JSON systems. New in version 2.1.
JSON_ESCAPE_SLASH Escape the / characters in strings with \e/. New in version 2.4.
JSON_REAL_PRECISION(n) Output all real numbers with at most n digits of precision. The valid range for n is between 0 and 31 (inclusive), and other values result in an undefined behavior. By default, the precision is 17, to correctly and losslessly encode all IEEE 754 double precision floating point numbers. New in version 2.7. NINDENT The following functions perform the actual JSON encoding. The result is in UTF-8. NDENT 0.0
char *json_dumps(const json_t *root, size_t flags) Returns the JSON representation of root as a string, or NULL on error. flags is described above. The return value must be freed by the caller using free(). NINDENT NDENT 0.0
int json_dumpf(const json_t *root, FILE *output, size_t flags) Write the JSON representation of root to the stream output. flags is described above. Returns 0 on success and -1 on error. If an error occurs, something may have already been written to output. In this case, the output is undefined and most likely not valid JSON. NINDENT NDENT 0.0
int json_dump_file(const json_t *json, const char *path, size_t flags) Write the JSON representation of root to the file path. If path already exists, it is overwritten. flags is described above. Returns 0 on success and -1 on error. NINDENT NDENT 0.0
json_dump_callback_t A typedef for a function that\(aqs called by json_dump_callback(): NDENT 7.0 NDENT 3.5
typedef int (*json_dump_callback_t)(const char *buffer, size_t size, void *data);NINDENT NINDENT buffer points to a buffer containing a chunk of output, size is the length of the buffer, and data is the corresponding json_dump_callback() argument passed through. On error, the function should return -1 to stop the encoding process. On success, it should return 0. New in version 2.2. NINDENT NDENT 0.0
int json_dump_callback(const json_t *json, json_dump_callback_t callback, void *data, size_t flags) Call callback repeatedly, passing a chunk of the JSON representation of root each time. flags is described above. Returns 0 on success and -1 on error. New in version 2.2. NINDENT
JSON_REJECT_DUPLICATES Issue a decoding error if any JSON object in the input text contains duplicate keys. Without this flag, the value of the last occurence of each key ends up in the result. Key equivalence is checked byte-by-byte, without special Unicode comparison algorithms. New in version 2.1.
JSON_DECODE_ANY By default, the decoder expects an array or object as the input. With this flag enabled, the decoder accepts any valid JSON value. Note: Decoding any value may be useful in some scenarios, but it\(aqs generally discouraged as it violates strict compatiblity with \%RFC 4627. If you use this flag, don\(aqt expect interoperatibility with other JSON systems. New in version 2.3.
JSON_DISABLE_EOF_CHECK By default, the decoder expects that its whole input constitutes a valid JSON text, and issues an error if there\(aqs extra data after the otherwise valid JSON input. With this flag enabled, the decoder stops after decoding a valid JSON array or object, and thus allows extra data after the JSON text. Normally, reading will stop when the last ] or } in the JSON input is encountered. If both JSON_DISABLE_EOF_CHECK and JSON_DECODE_ANY flags are used, the decoder may read one extra UTF-8 code unit (up to 4 bytes of input). For example, decoding 4true correctly decodes the integer 4, but also reads the t. For this reason, if reading multiple consecutive values that are not arrays or objects, they should be separated by at least one whitespace character. New in version 2.1.
JSON_DECODE_INT_AS_REAL JSON defines only one number type. Jansson distinguishes between ints and reals. For more information see real-vs-integer. With this flag enabled the decoder interprets all numbers as real values. Integers that do not have an exact double representation will silently result in a loss of precision. Integers that cause a double overflow will cause an error. New in version 2.5.
JSON_ALLOW_NUL Allow \eu0000 escape inside string values. This is a safety measure; If you know your input can contain NUL bytes, use this flag. If you don\(aqt use this flag, you don\(aqt have to worry about NUL bytes inside strings unless you explicitly create themselves by using e.g. json_stringn() or s# format specifier for json_pack(). Object keys cannot have embedded NUL bytes even if this flag is used. New in version 2.6. NINDENT Each function also takes an optional json_error_t parameter that is filled with error information if decoding fails. It\(aqs also updated on success; the number of bytes of input read is written to its position field. This is especially useful when using JSON_DISABLE_EOF_CHECK to read multiple consecutive JSON texts. New in version 2.3: Number of bytes of input read is written to the position field of the json_error_t structure. If no error or position information is needed, you can pass NULL. The following functions perform the actual JSON decoding. NDENT 0.0
json_t *json_loads(const char *input, size_t flags, json_error_t *error) Return value: New reference. Decodes the JSON string input and returns the array or object it contains, or NULL on error, in which case error is filled with information about the error. flags is described above. NINDENT NDENT 0.0
json_t *json_loadb(const char *buffer, size_t buflen, size_t flags, json_error_t *error) Return value: New reference. Decodes the JSON string buffer, whose length is buflen, and returns the array or object it contains, or NULL on error, in which case error is filled with information about the error. This is similar to json_loads() except that the string doesn\(aqt need to be null-terminated. flags is described above. New in version 2.1. NINDENT NDENT 0.0
json_t *json_loadf(FILE *input, size_t flags, json_error_t *error) Return value: New reference. Decodes the JSON text in stream input and returns the array or object it contains, or NULL on error, in which case error is filled with information about the error. flags is described above. This function will start reading the input from whatever position the input file was, without attempting to seek first. If an error occurs, the file position will be left indeterminate. On success, the file position will be at EOF, unless JSON_DISABLE_EOF_CHECK flag was used. In this case, the file position will be at the first character after the last ] or } in the JSON input. This allows calling json_loadf() on the same FILE object multiple times, if the input consists of consecutive JSON texts, possibly separated by whitespace. NINDENT NDENT 0.0
json_t *json_load_file(const char *path, size_t flags, json_error_t *error) Return value: New reference. Decodes the JSON text in file path and returns the array or object it contains, or NULL on error, in which case error is filled with information about the error. flags is described above. NINDENT NDENT 0.0
json_load_callback_t A typedef for a function that\(aqs called by json_load_callback() to read a chunk of input data: NDENT 7.0 NDENT 3.5
typedef size_t (*json_load_callback_t)(void *buffer, size_t buflen, void *data);NINDENT NINDENT buffer points to a buffer of buflen bytes, and data is the corresponding json_load_callback() argument passed through. On success, the function should return the number of bytes read; a returned value of 0 indicates that no data was read and that the end of file has been reached. On error, the function should return (size_t)-1 to abort the decoding process. New in version 2.4. NINDENT NDENT 0.0
json_t *json_load_callback(json_load_callback_t callback, void *data, size_t flags, json_error_t *error) Return value: New reference. Decodes the JSON text produced by repeated calls to callback, and returns the array or object it contains, or NULL on error, in which case error is filled with information about the error. data is passed through to callback on each call. flags is described above. New in version 2.4. NINDENT
/* Create the JSON integer 42 */
json_pack("i", 42);
/* Create the JSON array ["foo", "bar", true] */
json_pack("[ssb]", "foo", "bar", 1);
NINDENT NINDENT Here\(aqs the full list of format specifiers. The type in parentheses
denotes the resulting JSON type, and the type in brackets (if any)
denotes the C type that is expected as the corresponding argument or
arguments.
NDENT 0.0 s (string) [const char *] Convert a NULL terminated UTF-8 string to a JSON string.
s# (string) [const char *, int] Convert a UTF-8 buffer of a given length to a JSON string. New in version 2.5.
s% (string) [const char *, size_t] Like s# but the length argument is of type size_t. New in version 2.6.
+ [const char *] Like s, but concatenate to the previous string. Only valid after s, s#, + or +#. New in version 2.5.
+# [const char *, int] Like s#, but concatenate to the previous string. Only valid after s, s#, + or +#. New in version 2.5.
+% (string) [const char *, size_t] Like +# but the length argument is of type size_t. New in version 2.6.
n (null) Output a JSON null value. No argument is consumed.
b (boolean) [int] Convert a C int to JSON boolean value. Zero is converted to false and non-zero to true.
i (integer) [int] Convert a C int to JSON integer.
I (integer) [json_int_t] Convert a C json_int_t to JSON integer.
f (real) [double] Convert a C double to JSON real.
o (any value) [json_t *] Output any given JSON value as-is. If the value is added to an array or object, the reference to the value passed to o is stolen by the container.
O (any value) [json_t *] Like o, but the argument\(aqs reference count is incremented. This is useful if you pack into an array or object and want to keep the reference for the JSON value consumed by O to yourself.
[fmt] (array) Build an array with contents from the inner format string. fmt may contain objects and arrays, i.e. recursive value building is supported.
{fmt} (object) Build an object with contents from the inner format string fmt. The first, third, etc. format specifier represent a key, and must be a string (see s, s#, + and +# above), as object keys are always strings. The second, fourth, etc. format specifier represent a value. Any value may be an object or array, i.e. recursive value building is supported. NINDENT Whitespace, : and , are ignored. The following functions compose the value building API: NDENT 0.0
json_t *json_pack(const char *fmt, ...) Return value: New reference. Build a new JSON value according to the format string fmt. For each format specifier (except for {}[]n), one or more arguments are consumed and used to build the corresponding value. Returns NULL on error. NINDENT NDENT 0.0
json_t *json_pack_ex(json_error_t *error, size_t flags, const char *fmt, ...)
json_t *json_vpack_ex(json_error_t *error, size_t flags, const char *fmt, va_list ap) Return value: New reference. Like json_pack(), but an in the case of an error, an error message is written to error, if it\(aqs not NULL. The flags parameter is currently unused and should be set to 0. As only the errors in format string (and out-of-memory errors) can be caught by the packer, these two functions are most likely only useful for debugging format strings. NINDENT More examples: NDENT 0.0 NDENT 3.5
/* Build an empty JSON object */
json_pack("{}");
/* Build the JSON object {"foo": 42, "bar": 7} */
json_pack("{sisi}", "foo", 42, "bar", 7);
/* Like above, \(aq:\(aq, \(aq,\(aq and whitespace are ignored */
json_pack("{s:i, s:i}", "foo", 42, "bar", 7);
/* Build the JSON array [[1, 2], {"cool": true}] */
json_pack("[[i,i],{s:b}]", 1, 2, "cool", 1);
/* Build a string from a non-NUL terminated buffer */
char buffer[4] = {\(aqt\(aq, \(aqe\(aq, \(aqs\(aq, \(aqt\(aq};
json_pack("s#", buffer, 4);
/* Concatentate strings together to build the JSON string "foobarbaz" */
json_pack("s++", "foo", "bar", "baz");
NINDENT NINDENT s (string) [const char *] Convert a JSON string to a pointer to a NULL terminated UTF-8 string. The resulting string is extracted by using json_string_value() internally, so it exists as long as there are still references to the corresponding JSON string.
s% (string) [const char *, size_t *] Convert a JSON string to a pointer to a NULL terminated UTF-8 string and its length. New in version 2.6.
n (null) Expect a JSON null value. Nothing is extracted.
b (boolean) [int] Convert a JSON boolean value to a C int, so that true is converted to 1 and false to 0.
i (integer) [int] Convert a JSON integer to C int.
I (integer) [json_int_t] Convert a JSON integer to C json_int_t.
f (real) [double] Convert a JSON real to C double.
F (integer or real) [double] Convert a JSON number (integer or real) to C double.
o (any value) [json_t *] Store a JSON value with no conversion to a json_t pointer.
O (any value) [json_t *] Like O, but the JSON value\(aqs reference count is incremented.
[fmt] (array) Convert each item in the JSON array according to the inner format string. fmt may contain objects and arrays, i.e. recursive value extraction is supporetd.
{fmt} (object) Convert each item in the JSON object according to the inner format string fmt. The first, third, etc. format specifier represent a key, and must be s. The corresponding argument to unpack functions is read as the object key. The second fourth, etc. format specifier represent a value and is written to the address given as the corresponding argument. Note that every other argument is read from and every other is written to. fmt may contain objects and arrays as values, i.e. recursive value extraction is supporetd. New in version 2.3: Any s representing a key may be suffixed with a ? to make the key optional. If the key is not found, nothing is extracted. See below for an example.
! This special format specifier is used to enable the check that all object and array items are accessed, on a per-value basis. It must appear inside an array or object as the last format specifier before the closing bracket or brace. To enable the check globally, use the JSON_STRICT unpacking flag.
* This special format specifier is the opposite of !. If the JSON_STRICT flag is used, * can be used to disable the strict check on a per-value basis. It must appear inside an array or object as the last format specifier before the closing bracket or brace. NINDENT Whitespace, : and , are ignored. The following functions compose the parsing and validation API: NDENT 0.0
int json_unpack(json_t *root, const char *fmt, ...) Validate and unpack the JSON value root according to the format string fmt. Returns 0 on success and -1 on failure. NINDENT NDENT 0.0
int json_unpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, ...)
int json_vunpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, va_list ap) Validate and unpack the JSON value root according to the format string fmt. If an error occurs and error is not NULL, write error information to error. flags can be used to control the behaviour of the unpacker, see below for the flags. Returns 0 on success and -1 on failure. NINDENT NOTE: NDENT 0.0 NDENT 3.5 The first argument of all unpack functions is json_t *root instead of const json_t *root, because the use of O format specifier causes the reference count of root, or some value reachable from root, to be increased. Furthermore, the o format specifier may be used to extract a value as-is, which allows modifying the structure or contents of a value reachable from root. If the O and o format specifiers are not used, it\(aqs perfectly safe to cast a const json_t * variable to plain json_t * when used with these functions. NINDENT NINDENT The following unpacking flags are available: NDENT 0.0
JSON_STRICT Enable the extra validation step checking that all object and array items are unpacked. This is equivalent to appending the format specifier ! to the end of every array and object in the format string.
JSON_VALIDATE_ONLY Don\(aqt extract any data, just validate the JSON value against the given format string. Note that object keys must still be specified after the format string. NINDENT Examples: NDENT 0.0 NDENT 3.5
/* root is the JSON integer 42 */
int myint;
json_unpack(root, "i", &myint);
assert(myint == 42);
/* root is the JSON object {"foo": "bar", "quux": true} */
const char *str;
int boolean;
json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
assert(strcmp(str, "bar") == 0 && boolean == 1);
/* root is the JSON array [[1, 2], {"baz": null} */
json_error_t error;
json_unpack_ex(root, &error, JSON_VALIDATE_ONLY, "[[i,i], {s:n}]", "baz");
/* returns 0 for validation success, nothing is extracted */
/* root is the JSON array [1, 2, 3, 4, 5] */
int myint1, myint2;
json_unpack(root, "[ii!]", &myint1, &myint2);
/* returns -1 for failed validation */
/* root is an empty JSON object */
int myint = 0, myint2 = 0;
json_unpack(root, "{s?i, s?[ii]}",
"foo", &myint1,
"bar", &myint2, &myint3);
/* myint1, myint2 or myint3 is no touched as "foo" and "bar" don\(aqt exist */
NINDENT NINDENT int json_equal(json_t *value1, json_t *value2) Returns 1 if value1 and value2 are equal, as defined above. Returns 0 if they are inequal or one or both of the pointers are NULL. NINDENT
json_t *json_copy(json_t *value) Return value: New reference. Returns a shallow copy of value, or NULL on error. NINDENT NDENT 0.0
json_t *json_deep_copy(const json_t *value) Return value: New reference. Returns a deep copy of value, or NULL on error. NINDENT
json_malloc_t A typedef for a function pointer with malloc()\(aqs signature: NDENT 7.0 NDENT 3.5
typedef void *(*json_malloc_t)(size_t);NINDENT NINDENT NINDENT NDENT 0.0
json_free_t A typedef for a function pointer with free()\(aqs signature: NDENT 7.0 NDENT 3.5
typedef void (*json_free_t)(void *);NINDENT NINDENT NINDENT NDENT 0.0
void json_set_alloc_funcs(json_malloc_t malloc_fn, json_free_t free_fn) Use malloc_fn instead of malloc() and free_fn instead of free(). This function has to be called before any other Jansson\(aqs API functions to ensure that all memory operations use the same functions. NINDENT Examples: Circumvent problems with different CRT heaps on Windows by using application\(aqs malloc() and free(): NDENT 0.0 NDENT 3.5
json_set_alloc_funcs(malloc, free);NINDENT NINDENT Use the \%Boehm\(aqs conservative garbage collector for memory operations: NDENT 0.0 NDENT 3.5
json_set_alloc_funcs(GC_malloc, GC_free);NINDENT NINDENT Allow storing sensitive data (e.g. passwords or encryption keys) in JSON structures by zeroing all memory when freed: NDENT 0.0 NDENT 3.5
static void *secure_malloc(size_t size)
{
/* Store the memory area size in the beginning of the block */
void *ptr = malloc(size + 8);
*((size_t *)ptr) = size;
return ptr + 8;
}
static void secure_free(void *ptr)
{
size_t size;
ptr -= 8;
size = *((size_t *)ptr);
guaranteed_memset(ptr, 0, size + 8);
free(ptr);
}
int main()
{
json_set_alloc_funcs(secure_malloc, secure_free);
/* ... */
}
NINDENT NINDENT For more information about the issues of storing sensitive data in
memory, see
\%http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/protect-secrets.html.
The page also explains the guaranteed_memset() function used
in the example and gives a sample implementation for it.
.