.fp 5 CW

.TH STK 3

.SH NAME

\fBstk\fR \- data stack storage library

.SH SYNOPSIS

.ta .75i 1.5i 2.25i 3i 3.75i 4.5i 5.25i 6i

.PP

.nf

\f5

#include <stk.h>

Stk_t *stkopen(int \fIflags\fP);

Stk_t *stkinstall(Stk_t *\fIstack\fP, char *(\fIoverflow\fP)(int));

int stkclose(Stk_t *\fIstack\fP);

void stklink(Stk_t *\fIstack\fP)

char *stkalloc(Stk_t *\fIstack\fP, unsigned \fIsize\fP);

char *stkcopy(Stk_t *\fIstack\fP, const char *\fIstring\fP);

char *stkset(Stk_t *\fIstack\fP, char *\fIaddress\fP, unsigned \fIoffset\fP);

char *stkseek(Stk_t *\fIstack\fP, unsigned \fIoffset\fP);

int stktell(Stk_t *\fIstack\fP);

char *stkptr(Stk_t *\fIstack\fP, unsigned \fIoffset\fP);

char *stkfreeze(Stk_t *\fIstack\fP, unsigned \fIextra\fP);

int stkon(Stk *\fIstack\fP, char* \fIaddr\fP)

\fR

.fi

.SH DESCRIPTION

.PP

\f5stk\fP is a package of routines designed to provide efficient

stack oriented dynamic storage.

A stack abstraction consists of an ordered list of contiguous

memory regions, called stack frames, that can hold objects of

arbitrary size.

A stack is represented by the type \f5Stk_t\fP

defined in header \f5<stk.h>\fP.

The type \f5Stk_t\fP is compatible with the type \f5Sfio_t\fP

defined by the \f5sfio\fP(3) library.

At any instant there is one active stack which can be referenced

by the constant \f5stkstd\fP.

Variable size objects can be

added to the active stack

and programs can reference these objects directly with pointers.

In addition, the last object on the stack

(referred to here as the current object)

can be built incrementally.

The current object has an associated offset that determines its

current size.

While the current object is being built incrementally,

its location might

change so that it is necessary to reference the object with

relative offsets ranging from zero to the current offset of the object.

.PP

There is a preset initial active stack.

To use an additional stack, it is necessary to create it and to

install it as the active stack.

A stack is created with the \f5stkopen\fP() function.

A \fIflags\fP argument of \f5STK_SMALL\fP indicates that unused

space on the stack should be freed whenever this stack ceases

to be the active stack.

If successful,

\f5stkopen\fP() returns a pointer to a stack whose reference

count is 1.

Otherwise, \f5stkopen\fP() returns a null pointer.

The \f5stklink\fP() function increases the reference count for the

given \fIstack\fP.

The \f5stkinstall\fP() function

makes the specified \fIstack\fP the active stack and returns a pointer

to the previous active stack.

When the \fIoverflow\fP argument is not null,

it specifies a function that will

be called whenever \f5malloc\fP(3) fails while trying to grow the

stack.

The \fIoverflow\fP function will be called with the size that was passed

to \f5malloc\fP(3).

The \fIoverflow\fP function can call \f5exit\fP(3), call \f5longjmp\fP(3)

or return.

If the \f5overflow\fP function returns,

it must return a pointer to a memory region of the given size.

The default action is to write an error to standard error and to

call \f5exit\fP(2) with a non-zero exit value.

When \fIstack\fP is a null pointer,

the active stack is not changed

but the \fIoverflow\fP function for the active stack can be changed

and a pointer to the active stack is returned.

The \f5stkclose\fP() function decrements the reference count and

frees the memory associated with

the specified stack

when the reference count is zero.

The effect of subsequent references to objects

on the stack are undefined.

.PP

The

\f5stkalloc\fP() function returns an aligned pointer to space on the

active stack that can be used to hold any object of the given \fIsize\fP.

\f5stkalloc\fP() is similar to \f5malloc\fP(3) except that individual

items returned by \f5stkalloc\fP() can not be freed.

\f5stkalloc\fP() causes the offset of the current object to be set to

zero.

.PP

The

\f5stkcopy\fP() function copies the given string onto the stack

and returns a pointer to the \fIstring\fP on the stack.

\f5stkcopy\fP() causes the offset of the current object to be set to

zero.

.PP

The \f5stkset\fP() function finds the frame containing the given

\fIaddress\fP, frees all frames that were created after the one containing

the given \fIaddress\fP, and sets the current object to the given

\fIaddress\fP.

The top of the current object is set to \fIoffset\fP bytes from

current object.

If \fIaddress\fP is not the address of an object on the

stack the result is undefined.

.PP

The \f5sfio\fP(3) output functions can be used to build

current object incrementally.

An object that is built incrementally on the stack will

always occupy contiguous memory within a stack frame but

until \f5stkfreeze\fP() is called,

the location in memory for the object can change.

There is a current offset associated with the current object that

determines where subsequent operations apply.

Initially, this offset is zero, and the offset changes as a result

of the operations you specify.

The \f5stkseek\fP() function is used set the offset for the

current object.

The \fIoffset\fP argument to \f5stkseek\fP() specifies the new

offset for the current object.

The frame will be extended or moved

if \f5offset\fP causes the new current offset to extend beyond the

current frame.

\f5stkseek\fP() returns a pointer to the beginning of the current object.

The \f5stktell\fP() function gives the offset of the current object.

.PP

The \f5stkptr\fP() function converts the given \f5offset\fP

for the current object into a memory address on the stack.

This address is only valid until another stack operation is given.

The result is not defined if \fIoffset\fP exceeds the size of the current

object.

The \f5stkfreeze\fP()

function terminates the current object on the

stack and returns a pointer to the beginning of this object.

If \fIextra\fP is non-zero, \fIextra\fP bytes are added to the stack

before the current object is terminated. The first added byte will

contain zero and the contents of the remaining bytes are undefined.

.PP

The \f5stkon\fP()

function returns non-zero if the address given by \fIaddr\fP is

on the stack \fIstack\fP and \f50\fP otherwise.

.PP

.SH HISTORY

The

\f5stk\fP

interface was derived from similar routines in the KornShell code

that is used for building parse trees and carrying out expansions.

It provides an efficient mechanism for grouping dynamically allocated

objects so that they can be freed all at once rather than individually.

.SH AUTHOR

David Korn

.SH SEE ALSO

\f5exit(2)\fP

\f5longjmp(3)\fP

\f5malloc(3)\fP

\f5sfio(3)\fP