malloc, free, realloc, calloc, alloca - memory allocator
void *realloc(ptr, size)
void *calloc(nelem, elsize)
size_t nelem, elsize;
The and subroutines provide a simple general-purpose memory allocation
package. The subroutine returns a pointer to a block of at least size
bytes beginning on a word boundary.
The argument to is a pointer to a block previously allocated by This
space is made available for further allocation, but its contents are
Needless to say, grave disorder will result if the space assigned by is
overrun or if some random number is handed to
The subroutine maintains multiple lists of free blocks according to
size, allocating space from the appropriate list. It calls to get more
memory from the system when there is no suitable space already free.
For further information, see
The subroutine changes the size of the block pointed to by ptr to size
bytes and returns a pointer to the (possibly moved) block. The con‐
tents will be unchanged up to the lesser of the new and old sizes.
If ptr is a null pointer, then behaves like for the specified size. If
size is zero, then frees the space pointed to by ptr.
In order to be compatible with older versions, also works if ptr points
to a block freed since the last call of or Sequences of and were previ‐
ously used to attempt storage compaction. This procedure is no longer
The subroutine allocates space for an array of nelem elements of size
elsize. The space is initialized to zeros.
The subroutine allocates size bytes of space in the stack frame of the
caller. This temporary space is automatically freed on return.
Each of the allocation routines returns a pointer to space suitably
aligned (after possible pointer coercion) for storage of any type of
When returns 0, the block pointed to by ptr may be destroyed.
Currently, the allocator is unsuitable for direct use in a large vir‐
tual environment where many small blocks are kept, since it keeps all
allocated and freed blocks on a circular list. Just before more memory
is allocated, all allocated and freed blocks are referenced.
The subroutine is machine dependent.
The and 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.
The and subroutines will fail and no additional memory will be allo‐
cated if one of the following is true:
[ENOMEM] The limit, as set by is exceeded.
[ENOMEM] The maximum possible size of a data segment (compiled into
the system) is exceeded.
[ENOMEM] Insufficient space exists in the swap area to support the