VBox-CodingGuidelines.cpp revision c58f1213e628a545081c70e26c6b67a841cff880
/* $Id$ */
/** @file
* VBox - Coding Guidelines.
*/
/*
* Copyright (C) 2006-2012 Oracle Corporation
*
* This file is part of VirtualBox Open Source Edition (OSE), as
* available from http://www.virtualbox.org. This file is free software;
* General Public License (GPL) as published by the Free Software
* Foundation, in version 2 as it comes in the "COPYING" file of the
* VirtualBox OSE distribution. VirtualBox OSE is distributed in the
* hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
*/
/** @page pg_vbox_guideline VBox Coding Guidelines
*
* The VBox Coding guidelines are followed by all of VBox with the exception of
* qemu. Qemu is using whatever the frenchman does.
*
* There are a few compulsory rules and a bunch of optional ones. The following
* sections will describe these in details. In addition there is a section of
* Subversion 'rules'.
*
*
*
* @section sec_vbox_guideline_compulsory Compulsory
*
*
* - The indentation size is 4 chars.
*
* - Tabs are only ever used in makefiles.
*
* - Use RT and VBOX types.
*
* - Use Runtime functions.
*
* - Use the standard bool, uintptr_t, intptr_t and [u]int[1-9+]_t types.
*
* - Avoid using plain unsigned and int.
*
* - Use static wherever possible. This makes the namespace less polluted
* and avoids nasty name clash problems which can occur, especially on
* Unix-like systems. (1)
*
* - Public names are of the form Domain[Subdomain[]]Method, using mixed
* casing to mark the words. The main domain is all uppercase.
*
* - Public names are always declared using the appropriate DECL macro. (2)
*
* - Internal names starts with a lowercased main domain.
*
* - Defines are all uppercase and separate words with underscore.
* This applies to enum values too.
*
* - Typedefs are all uppercase and contain no underscores to distinguish
* them from defines.
*
* - Pointer typedefs start with 'P'. If pointer to const then 'PC'.
*
* - Function typedefs start with 'FN'. If pointer to FN then 'PFN'.
*
* - All files are case sensitive.
*
* - Slashes are unix slashes ('/') runtime converts when necessary.
*
* - char strings are UTF-8.
*
* - All functions return VBox status codes. There are three general
* exceptions from this:
* -# Predicate functions. These are function which are boolean in
* nature and usage. They return bool. The function name will
* include 'Has', 'Is' or similar.
* -# Functions which by nature cannot possibly fail.
* These return void.
* -# "Get"-functions which return what they ask for.
* A get function becomes a "Query" function if there is any
* doubt about getting what is ask for.
*
* - VBox status codes have three subdivisions:
* -# Errors, which are VERR_ prefixed and negative.
* -# Warnings, which are VWRN_ prefixed and positive.
* -# Informational, which are VINF_ prefixed and positive.
*
*
* - Other useful constructs are also put in the IPRT.
*
* - The code shall not cause compiler warnings. Check this on ALL
* the platforms.
*
* - All files have file headers with $Id and a file tag which describes
* the file in a sentence or two.
* Note: Remember to enable keyword expansion when adding files to svn.
*
* - All public functions are fully documented in Doxygen style using the
* javadoc dialect (using the 'at' instead of the 'slash' as
* commandprefix.)
*
* - All structures in header files are described, including all their
* members.
*
* - All modules have a documentation 'page' in the main source file which
* describes the intent and actual implementation.
*
* - Code which is doing things that are not immediately comprehensible
* shall include explanatory comments.
*
* - Documentation and comments are kept up to date.
*
* comments, only ANSI C comments!
*
* - Comments on \#else indicates what begins while the comment on a
* \#endif indicates what ended.
*
*
* (1) It is common practice on Unix to have a single symbol namespace for an
* entire process. If one is careless symbols might be resolved in a
* different way that one expects, leading to weird problems.
*
* (2) This is common practice among most projects dealing with modules in
* shared libraries. The Windows / PE __declspect(import) and
* __declspect(export) constructs are the main reason for this.
* OTOH, we do perhaps have a bit too detailed graining of this in VMM...
*
*
* @subsection sec_vbox_guideline_compulsory_sub64 64-bit and 32-bit
*
* Here are some amendments which address 64-bit vs. 32-bit portability issues.
*
* Some facts first:
*
* - On 64-bit Windows the type long remains 32-bit. On nearly all other
* 64-bit platforms long is 64-bit.
*
* - On all 64-bit platforms we care about, int is 32-bit, short is 16 bit
* and char is 8-bit.
* (I don't know about any platforms yet where this isn't true.)
*
* - size_t, ssize_t, uintptr_t, ptrdiff_t and similar are all 64-bit on
* 64-bit platforms. (These are 32-bit on 32-bit platforms.)
*
* - There is no inline assembly support in the 64-bit Microsoft compilers.
*
*
* Now for the guidelines:
*
* - Never, ever, use int, long, ULONG, LONG, DWORD or similar to cast a
* pointer to integer. Use uintptr_t or intptr_t. If you have to use
*
* - RT_OS_WINDOWS is defined to indicate Windows. Do not use __WIN32__,
* __WIN64__ and __WIN__ because they are all deprecated and scheduled
* for removal (if not removed already). Do not use the compiler
* defined _WIN32, _WIN64, or similar either. The bitness can be
* determined by testing ARCH_BITS.
* Example:
* @code
* #ifdef RT_OS_WINDOWS
* // call win32/64 api.
* #endif
* #ifdef RT_OS_WINDOWS
* # if ARCH_BITS == 64
* // call win64 api.
* # else // ARCH_BITS == 32
* // call win32 api.
* # endif // ARCH_BITS == 32
* #else // !RT_OS_WINDOWS
* // call posix api
* #endif // !RT_OS_WINDOWS
* @endcode
*
* - There are RT_OS_xxx defines for each OS, just like RT_OS_WINDOWS
* mentioned above. Use these defines instead of any predefined
* compiler stuff or defines from system headers.
*
* - RT_ARCH_X86 is defined when compiling for the x86 the architecture.
* Do not use __x86__, __X86__, __[Ii]386__, __[Ii]586__, or similar
* for this purpose.
*
* - RT_ARCH_AMD64 is defined when compiling for the AMD64 architecture.
* Do not use __AMD64__, __amd64__ or __x64_86__.
*
* - Take care and use size_t when you have to, esp. when passing a pointer
* to a size_t as a parameter.
*
* - Be wary of type promotion to (signed) integer. For example the
* following will cause u8 to be promoted to int in the shift, and then
* sign extended in the assignment 64-bit:
* @code
* uint8_t u8 = 0xfe;
* uint64_t u64 = u8 << 24;
* // u64 == 0xfffffffffe000000
* @endcode
*
*
* @subsection sec_vbox_guideline_compulsory_cppmain C++ guidelines for Main
*
* Main is currently (2009) full of hard-to-maintain code that uses complicated
* templates. The new mid-term goal for Main is to have less custom templates
* instead of more for the following reasons:
*
* - Template code is harder to read and understand. Custom templates create
* territories which only the code writer understands.
*
* - Errors in using templates create terrible C++ compiler messages.
*
* - Template code is really hard to look at in a debugger.
*
* - Templates slow down the compiler a lot.
*
* In particular, the following bits should be considered deprecated and should
* NOT be used in new code:
*
* - everything in include/iprt/cpputils.h (auto_ref_ptr, exception_trap_base,
* char_auto_ptr and friends)
*
* Generally, in many cases, a simple class with a proper destructor can achieve
* the same effect as a 1,000-line template include file, and the code is
* much more accessible that way.
*
* Using standard STL templates like std::list, std::vector and std::map is OK.
* Exceptions are:
*
* - Guest Additions because we don't want to link against libstdc++ there.
*
* - std::string should not be used because we have iprt::MiniString and
* com::Utf8Str which can convert efficiently with COM's UTF-16 strings.
*
* - std::auto_ptr<> in general; that part of the C++ standard is just broken.
* Write a destructor that calls delete.
*
*
* @subsection sec_vbox_guideline_compulsory_cppqtgui C++ guidelines for the Qt GUI
*
* The Qt GUI is currently (2010) on its way to become more compatible to the
* rest of VirtualBox coding style wise. From now on, all the coding style
* rules described in this file are also mandatory for the Qt GUI. Additionally
* the following rules should be respected:
*
* - GUI classes which correspond to GUI tasks should be prefixed by UI (no VBox anymore)
*
* - Classes which extents some of the Qt classes should be prefix by QI
*
* - General task classes should be prefixed by C
*
* - Slots are prefixed by slt -> sltName
*
* - Signals are prefixed by sig -> sigName
*
* - Use Qt classes for lists, strings and so on, the use of STL classes should
* be avoided
*
* - All files like .cpp, .h, .ui, which belong together are located in the
* same directory and named the same
*
*
* @section sec_vbox_guideline_optional Optional
*
* First part is the actual coding style and all the prefixes. The second part
* is a bunch of good advice.
*
*
* @subsection sec_vbox_guideline_optional_layout The code layout
*
* - Max line length is 130 chars. Exceptions are table-like
* code/initializers and Log*() statements (don't waste unnecessary
* vertical space on debug logging).
*
* - Comments should try stay within the usual 80 columns as these are
* denser and too long lines may be harder to read.
*
* - Curly brackets are not indented. Example:
* @code
* if (true)
* {
* Something1();
* Something2();
* }
* else
* {
* SomethingElse1().
* SomethingElse2().
* }
* @endcode
*
* - Space before the parentheses when it comes after a C keyword.
*
* - No space between argument and parentheses. Exception for complex
* expression. Example:
* @code
* if (PATMR3IsPatchGCAddr(pVM, GCPtr))
* @endcode
*
* - The else of an if is always the first statement on a line. (No curly
* stuff before it!)
*
* - else and if go on the same line if no { compound statement }
* follows the if. Example:
* @code
* if (fFlags & MYFLAGS_1)
* fFlags &= ~MYFLAGS_10;
* else if (fFlags & MYFLAGS_2)
* {
* fFlags &= ~MYFLAGS_MASK;
* fFlags |= MYFLAGS_5;
* }
* else if (fFlags & MYFLAGS_3)
* @endcode
*
*
* - Slightly complex boolean expressions are split into multiple lines,
* putting the operators first on the line and indenting it all according
* to the nesting of the expression. The purpose is to make it as easy as
* possible to read. Example:
* @code
* if ( RT_SUCCESS(rc)
* || (fFlags & SOME_FLAG))
* @endcode
*
* - When 'if' or 'while' statements gets long, the closing parentheses
* goes right below the opening parentheses. This may be applied to
* sub-expression. Example:
* @code
* if ( RT_SUCCESS(rc)
* || ( fSomeStuff
* && fSomeOtherStuff
* && fEvenMoreStuff
* )
* || SomePredicateFunction()
* )
* {
* ...
* }
* @endcode
*
* - The case is indented from the switch (to avoid having the braces for
* the 'case' at the same level as the 'switch' statement).
*
* - If a case needs curly brackets they contain the entire case, are not
* indented from the case, and the break or return is placed inside them.
* Example:
* @code
* switch (pCur->eType)
* {
* case PGMMAPPINGTYPE_PAGETABLES:
* {
* unsigned iPDE = pCur->GCPtr >> PGDIR_SHIFT;
* unsigned iPT = (pCur->GCPtrEnd - pCur->GCPtr) >> PGDIR_SHIFT;
* while (iPT-- > 0)
* if (pPD->a[iPDE + iPT].n.u1Present)
* return VERR_HYPERVISOR_CONFLICT;
* break;
* }
* }
* @endcode
*
* - In a do while construction, the while is on the same line as the
* closing "}" if any are used.
* Example:
* @code
* do
* {
* stuff;
* i--;
* } while (i > 0);
* @endcode
*
* - Comments are in C style. C++ style comments are used for temporary
* disabling a few lines of code.
*
* - No unnecessary parentheses in expressions (just don't over do this
* so that gcc / msc starts bitching). Find a correct C/C++ operator
* precedence table if needed.
*
* - 'for (;;)' is preferred over 'while (true)' and 'while (1)'.
*
* - Parameters are indented to the start parentheses when breaking up
* function calls, declarations or prototypes. (This is in line with
* how 'if', 'for' and 'while' statements are done as well.) Example:
* @code
* RTPROCESS hProcess;
* int rc = RTProcCreateEx(papszArgs[0],
* papszArgs,
* RTENV_DEFAULT,
* fFlags,
* NULL, // phStdIn
* NULL, // phStdOut
* NULL, // phStdErr
* NULL, // pszAsUser
* NULL, // pszPassword
* &hProcess);
* @endcode
*
* - That Dijkstra is dead is no excuse for using gotos.
*
*
*
* @subsection sec_vbox_guideline_optional_prefix Variable / Member Prefixes
*
* therefore avoid using prefixes that just indicating the type if a better
* choice is available.
*
*
* The prefixes:
*
* - The 'g_' (or 'g') prefix means a global variable, either on file or module level.
*
* - The 's_' (or 's') prefix means a static variable inside a function or class.
*
* - The 'm_' (or 'm') prefix means a class data member.
*
* In new code in Main, use "m_" (and common sense). As an exception,
* in Main, if a class encapsulates its member variables in an anonymous
* structure which is declared in the class, but defined only in the
* implementation (like this: 'class X { struct Data; Data *m; }'), then
* the pointer to that struct is called 'm' itself and its members then
* need no prefix, because the members are accessed with 'm->member'
* already which is clear enough.
*
* - The 'a_' prefix means a parameter (argument) variable. This is
* sometimes written 'a' in parts of the source code that does not use
* the array prefix.
*
* - The 'p' prefix means pointer. For instance 'pVM' is pointer to VM.
*
* - The 'r' prefix means that something is passed by reference.
*
* - The 'k' prefix means that something is a constant. For instance
* 'enum { kStuff };'. This is usually not used in combination with
* 'p', 'r' or any such thing, it's main main use is to make enums
* easily identifiable.
*
* - The 'a' prefix means array. For instance 'aPages' could be read as
* array of pages.
*
* - The 'c' prefix means count. For instance 'cbBlock' could be read,
* count of bytes in block.
*
* - The 'cx' prefix means width (count of 'x' units).
*
* - The 'cy' prefix means height (count of 'y' units).
*
* - The 'x', 'y' and 'z' prefix refers to the x-, y- , and z-axis
* respectively.
*
* - The 'off' prefix means offset.
*
* - The 'i' or 'idx' prefixes usually means index. Although the 'i' one
* can sometimes just mean signed integer.
*
* - The 'i[1-9]+' prefix means a fixed bit size variable. Frequently
* used with the int[1-9]+_t types where the width is really important.
* In most cases 'i' is more appropriate. [type]
*
* - The 'e' (or 'enm') prefix means enum.
*
* - The 'u' prefix usually means unsigned integer. Exceptions follows.
*
* - The 'u[1-9]+' prefix means a fixed bit size variable. Frequently
* used with the uint[1-9]+_t types and with bitfields where the width is
* really important. In most cases 'u' or 'b' (byte) would be more
* appropriate. [type]
*
* - The 'b' prefix means byte or bytes. [type]
*
* - The 'f' prefix means flags. Flags are unsigned integers of some kind
* or booleans.
*
* - TODO: need prefix for real float. [type]
*
* - The 'rd' prefix means real double and is used for 'double' variables.
* [type]
*
* - The 'lrd' prefix means long real double and is used for 'long double'
* variables. [type]
*
* - The 'ch' prefix means a char, the (signed) char type. [type]
*
*
* - The 'uc' prefix means a Unicode Code point, the RTUNICP type. [type]
*
* - The 'uch' prefix means unsigned char. It's rarely used. [type]
*
* - The 'sz' prefix means zero terminated character string (array of
* chars). (UTF-8)
*
* (array of RTUTF16).
*
* - The 'usz' prefix means zero terminated Unicode string (array of
* RTUNICP).
*
* - The 'str' prefix means C++ string; either a std::string or, in Main,
* a Utf8Str or, in Qt, a QString. When used with 'p', 'r', 'a' or 'c'
* the first letter should be capitalized.
*
* - The 'bstr' prefix, in Main, means a UTF-16 Bstr. When used with 'p',
* 'r', 'a' or 'c' the first letter should be capitalized.
*
* - The 'pfn' prefix means pointer to function. Common usage is 'pfnCallback'
* and such like.
*
* - The 'psz' prefix is a combination of 'p' and 'sz' and thus means
* pointer to a zero terminated character string. (UTF-8)
*
* - The 'pcsz' prefix is used to indicate constant string pointers in
* parts of the code. Most code uses 'psz' for const and non-const
* string pointers.
*
* - The 'l' prefix means (signed) long. We try avoid using this,
* expecially with the 'LONG' types in Main as these are not 'long' on
* 64-bit non-Windows platforms and can cause confusion. Alternatives:
* 'i' or 'i32'. [type]
*
* - The 'ul' prefix means unsigned long. We try avoid using this,
* expecially with the 'ULONG' types in Main as these are not 'unsigned
* long' on 64-bit non-Windows platforms and can cause confusion.
* Alternatives: 'u' or 'u32'. [type]
*
*
* @subsection sec_vbox_guideline_optional_misc Misc / Advice / Stuff
*
* - When writing code think as the reader.
*
* - When writing code think as the compiler. (2)
*
* - When reading code think as if it's full of bugs - find them and fix them.
*
* - Pointer within range tests like:
* @code
* if ((uintptr_t)pv >= (uintptr_t)pvBase && (uintptr_t)pv < (uintptr_t)pvBase + cbRange)
* @endcode
* Can also be written as (assuming cbRange unsigned):
* @code
* if ((uintptr_t)pv - (uintptr_t)pvBase < cbRange)
* @endcode
* Which is shorter and potentially faster. (1)
*
* - Avoid unnecessary casting. All pointers automatically cast down to
* void *, at least for non class instance pointers.
*
* - It's very very bad practise to write a function larger than a
* screen full (1024x768) without any comprehensibility and explaining
* comments.
*
* - More to come....
*
*
* (1) Important, be very careful with the casting. In particular, note that
* a compiler might treat pointers as signed (IIRC).
*
* (2) "A really advanced hacker comes to understand the true inner workings of
* the machine - he sees through the language he's working in and glimpses
* the secret functioning of the binary code - becomes a Ba'al Shem of
* sorts." (Neal Stephenson "Snow Crash")
*
*
*
* @section sec_vbox_guideline_warnings Compiler Warnings
*
* The code should when possible compile on all platforms and compilers without any
* warnings. That's a nice idea, however, if it means making the code harder to read,
* less portable, unreliable or similar, the warning should not be fixed.
*
* Some of the warnings can seem kind of innocent at first glance. So, let's take the
* most common ones and explain them.
*
*
* @subsection sec_vbox_guideline_warnings_signed_unsigned_compare Signed / Unsigned Compare
*
* GCC says: "warning: comparison between signed and unsigned integer expressions"
*
* The following example will not output what you expect:
@code
#include <stdio.h>
int main()
{
signed long a = -1;
unsigned long b = 2294967295;
if (a < b)
printf("%ld < %lu: true\n", a, b);
else
printf("%ld < %lu: false\n", a, b);
return 0;
}
@endcode
* If I understood it correctly, the compiler will convert a to an
* unsigned long before doing the compare.
*
*
*
* @section sec_vbox_guideline_svn Subversion Commit Rules
*
*
* Before checking in:
*
* - Check Tinderbox and make sure the tree is green across all platforms. If it's
* red on a platform, don't check in. If you want, warn in the \#vbox channel and
* help make the responsible person fix it.
* NEVER CHECK IN TO A BROKEN BUILD.
*
* - When checking in keep in mind that a commit is atomic and that the Tinderbox and
* developers are constantly checking out the tree. Therefore do not split up the
* commit unless it's into 100% independent parts. If you need to split it up in order
* to have sensible commit comments, make the sub-commits as rapid as possible.
*
* - If you make a user visible change, such as fixing a reported bug,
* make sure you add an entry to doc/manual/user_ChangeLogImpl.xml.
*
* - If you are adding files make sure set the right attributes.
*
*
* After checking in:
*
* - After checking-in, you watch Tinderbox until your check-ins clear. You do not
* go home. You do not sleep. You do not log out or experiment with drugs. You do
* not become unavailable. If you break the tree, add a comment saying that you're
* fixing it. If you can't fix it and need help, ask in the \#innotek channel or back
* out the change.
*
* (Inspired by mozilla tree rules.)
*/