MALLOC(3F)MALLOC(3F)NAME
malloc, free - main memory allocator
FORTRAN SYNOPSIS
pointer (iptr, arr)
dimension arr(1)
integer nbytes
iptr = malloc(nbytes)
call free(iptr)DESCRIPTIONmalloc and free provide a simple general-purpose memory allocation
package. malloc returns a pointer to a block of at least nbytes bytes
suitably aligned for any use.
arr can be an array of any type. After the call to malloc the array arr
can be used as if it has been declared as an array with nbytes in length.
All references to this array will be deferenced using the value assigned
to iptr in the malloc call to refer to the space allocated by malloc.
The argument to free is a pointer to a block previously allocated by
malloc; after free is performed this space is made available for further
allocation, but its contents are left undisturbed.
Undefined results will occur 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
brk(2)] to get more memory from the system when there is no suitable
space already free.
DIAGNOSTICS
malloc, returns a NULL pointer if there is no available memory or if the
arena has been detectably corrupted by storing outside the bounds of a
block. When this happens the block pointed to by iptr may be destroyed.
NOTES
Search time increases when many objects have been allocated; that is, if
a program allocates but never frees, then each successive allocation
takes longer.
Note that the system may be configured with virtual swap space. This
allows processes to allocate more virtual memory than is actually
available, allowing the use of sparse addressing, successful forks and
subsequent execs by programs larger than 1/2 the available virtual
memory, and so forth. Thus programs using malloc may get a successful
return, but later be sent the SIGKILL signal if virtual memory was
overcommitted, and processes attempt to actually use all of the
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MALLOC(3F)MALLOC(3F)
overcommitted memory. If the system has no virtual swap space
configured, then processes are limited to using no more virtual memory
than the sum of physical memory and swap space. See the section on
"Logical Swap Space" in the swap(1M) man page for more information.
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