MALLOC

Section: MINTLIB LIBRARY FUNCTIONS (3)
Updated: 3 March 1993
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NAME

malloc, free, realloc, calloc, alloca - memory allocator

SYNOPSIS

#include <stdlib.h>

void *malloc(size_t size);

void free(void *ptr);

void *realloc(void *ptr, size_t size);

void *calloc(size_t num_elems, size_t elem_size);

void *alloca(size_t size);

DESCRIPTION

These routines provide a general-purpose memory allocation package. They maintain a table of free blocks for efficient allocation and coalescing of free storage. When there is no suitable space already free, the allocation routines call Malloc to get more memory from the system. Each of the allocation routines returns a pointer to space suitably aligned for storage of any type of object. Each returns a NULL pointer if the request cannot be completed or if an area of size zero is requested. malloc returns a pointer to a block of at least size bytes. free releases a previously allocated block. Its argument is a pointer to a block previously allocated by malloc, calloc or realloc. realloc changes the size of a block referenced to by ptr to size bytes and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes. If unable to honor a reallocation request, realloc leaves it first argument unaltered. Using realloc with a block freed before is an error. realloc(NULL, size) is the same as malloc(size). realloc(ptr, 0) is the same as free(ptr). calloc uses malloc to allocate space for an array of num_elems elements of size elem_size, initialises the space to zeros, and returns a pointer to the initialised block. alloca allocates size bytes of space in the stack frame of the caller, and returns a pointer to the allocated block. This temporary space is automatically freed when the caller returns. Note that if the allocated block is beyond the current stack limit, the resulting behavior is undefined.

RETURN VALUES

On success, malloc, calloc, realloc and alloca return a pointer to space suitably aligned for storage of any type of object. On failure, they return NULL.

WARNINGS

On UN*X machines, malloc and realloc return a non-NULL pointer if size is 0, and calloc returns a non-NULL pointer if num_elems or elem_size is 0. The mintlibs follow the ANSI-C standard and return NULL in these circumstances. alloca is machine-, compiler-, and most of all, system- dependent. Its use is strongly discouraged.

NOTES

GNU software is uncommonly fond of alloca. To use alloca with Pure-C in the current version of the mintlibs, the caller must be compiled with the -S option set or the program will crash.

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