MALLOC(3) MALLOC(3) NAME malloc, free, realloc, ialloc, calloc, cfree - main memory allocator SYNOPSIS char *malloc(size) unsigned size; free(ptr) char *ptr; char *realloc(ptr, size) char *ptr; unsigned size; ialloc(ptr, size) char *ptr; unsigned size; char *calloc(nelem, elsize) unsigned nelem, elsize; cfree(ptr) char *ptr; DESCRIPTION Malloc and free provide a simple general-purpose memory allocation package. Malloc returns a pointer to a new block of at least size bytes. The argument to free is a pointer to a block previously allocated by malloc; this space is made available for fur- ther allocation. The present implementation of free does not change the contents; but it is unwise to depend on this fact. Realloc changes the size of the block pointed 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. Ialloc inserts into the arena a designated block of store that was not previously known to the allocator. Calloc allocates space for an array of nelem elements of size elsize. The space is initialized to zeros. Cfree frees such a block. Each of the allocation routines returns a pointer to space suitably aligned (after possible pointer coercion) for MALLOC(3) MALLOC(3) storage of any type of object. The arena, though not necessarily contiguous, is kept in strict address order. Malloc allocates the first big enough contiguous reach of free space found in a circular search from the last block allocated or freed, coalescing adjacent free blocks as it searches. It calls sbrk (see break(2)) to get more memory from the system when there is no suitable space already free. It has been arranged that realloc will work on a block that has been freed, provided no other allo- cations have intervened. This questionable, unportable practice allows combinations of free, realloc and malloc to be used to rearrange the arena. SEE ALSO galloc(3), sbrk(2) DIAGNOSTICS Malloc, realloc and calloc return a null pointer (0) if there is no available memory or if the arena has been detectably corrupted by storing outside the bounds of a block. A very stringently checking version of malloc, which aborts with a diagnostic if the arena is corrupted, can be created by recompilation with a debugging flag set; see the source. BUGS When realloc returns 0, the block pointed to by ptr may be destroyed. Malloc is general, not fast. A program that repeatedly allocates and frees a particular kind of block often can be speeded up by superimposing a block-cacheing or suballoca- tion scheme on top of malloc-free.