malloc(3)
NAME
malloc, free, realloc, calloc − main memory allocator
SYNTAX
char *malloc(size)
unsigned size;
void free(ptr)
char *ptr;
char *realloc(ptr, size)
char *ptr;
unsigned size;
char *calloc(nelem, elsize)
unsigned nelem, elsize;
DESCRIPTION
The malloc and free subroutines provide a simple general-purpose memory allocation package. The malloc subroutine 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.
Disorder will result if the space assigned by malloc is overrun or if some random number is handed to free.
The malloc subroutine allocates the first large enough contiguous reach of free space found in a circular search from the last block allocated or freed, joining adjacent free blocks as it searches. It calls the sbrk system call to get more memory from the system when there is no suitable space already free. For further information, see brk(2).
The realloc subroutine 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.
The realloc subroutine 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.
The calloc subroutine allocates space for an array of nelem elements of size elsize. The space is initialized to zeros.
Each of the allocation routines returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object.
RESTRICTIONS
When realloc returns 0, the block pointed to by ptr may be destroyed.
DIAGNOSTICS
The malloc, realloc and calloc subroutines 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.