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malloc, free, realloc, calloc - main memory allocator
char *realloc(ptr, size)
char *calloc(nelem, elsize)
unsigned nelem, elsize;
Malloc and free provide a simple general-purpose memory allocation package. Malloc
returns a pointer to a block of at least size bytes beginning on a word boundary.
The argument to free is a pointer to a block previously allocated by malloc; this space is
made available for further allocation, but its contents are left undisturbed.
Needless to say, grave disorder will result if the space assigned by malloc is overrun or
if some random number is handed to free.
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.
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.
Realloc also works if ptr points to a block freed since the last call of malloc, realloc
or calloc; thus sequences of free, malloc and realloc can exploit the search strategy of
malloc to do storage compaction.
Calloc allocates space for an array of nelem elements of size elsize. The space is ini-
tialized to zeros.
Each of the allocation routines returns a pointer to space suitably aligned (after possi-
ble pointer coercion) for storage of any type of object.
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. Malloc
may be recompiled to check the arena very stringently on every transaction; see the source
When realloc returns 0, the block pointed to by ptr may be destroyed.
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