man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

bsdmalloc(3MALLOC)

Name

bsdmalloc - memory allocator

Synopsis

cc [ flag ... ] file ... –lbsdmalloc [ library ... ]

char *malloc(sizeunsigned size;

int free( ptrchar *ptr;

char *realloc( ptr, sizechar *ptr;
unsigned size;

Description

These routines provide a general-purpose memory allocation package. They maintain a table of free blocks for efficient allocation and coalescing of free storage. When there is no suitable space already free, the allocation routines call sbrk(2) to get more memory from the system. Each of the allocation routines returns a pointer to space suitably aligned for storage of any type of object. Each returns a null pointer if the request cannot be completed.

The malloc() function returns a pointer to a block of at least size bytes, which is appropriately aligned.

The free() function releases a previously allocated block. Its argument is a pointer to a block previously allocated by malloc() or realloc(). The free() function does not set errno.

The realloc() function 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. If the new size of the block requires movement of the block, the space for the previous instantiation of the block is freed. If the new size is larger, the contents of the newly allocated portion of the block are unspecified. If ptr is NULL, realloc() behaves like malloc() for the specified size. If size is 0 and ptr is not a null pointer, the space pointed to is freed.

Return Values

The malloc() and realloc() functions return a null pointer if there is not enough available memory. They return a non-null pointer if size is 0. These pointers should not be dereferenced. When realloc() returns NULL, the block pointed to by ptr is left intact. Always cast the value returned by malloc() and realloc().

Errors

If malloc() or realloc() returns unsuccessfully, errno will be set to indicate the following:

ENOMEM

size bytes of memory cannot be allocated because it exceeds the physical limits of the system.

EAGAIN

There is not enough memory available at this point in time to allocate size bytes of memory; but the application could try again later.

Usage

Using realloc() with a block freed before the most recent call to malloc() or realloc() results in an error.

Comparative features of the various allocation libraries can be found in the umem_alloc(3MALLOC) manual page.

See Also

brk(2), malloc(3C), malloc(3MALLOC), mapmalloc(3MALLOC), umem_alloc(3MALLOC)

Warnings

Use of libbsdmalloc renders an application non-SCD compliant.

The libbsdmalloc routines are incompatible with the memory allocation routines in the standard C-library (libc): malloc(3C), alloca(3C), calloc(3C), free(3C), memalign(3C), realloc(3C), and valloc(3C).