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Name

Synopsis

cc [ flag ... ] file ... -lmalloc [ library ... ]

#include <stdlib.h>

void *malloc(size_t size);

void free(void *ptr);

void *realloc(void *ptr, size_t size);

void *calloc(size_t nelem, size_t elsize);

#include <malloc.h>

int mallopt(int cmd, int value);

struct mallinfo mallinfo(void);

MT-Level

Safe

Description

malloc() returns a pointer to a block of at least size bytes suitably aligned for any use.

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, and its contents have been destroyed (but see mallopt() below for a way to change this behavior). If ptr is a null pointer, no action occurs.

Undefined results occur if the space assigned by malloc() is overrun or if some random number is handed to 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 are unchanged up to the lesser of the new and old sizes. If ptr is a null pointer, realloc() behaves like malloc() for the specified size. If size is zero and ptr is not a null pointer, the object it points to is freed.

calloc() allocates space for an array of nelem elements of size elsize. The space is initialized to zeros.

mallopt() provides for control over the allocation algorithm. The available values for cmd are:

M_MXFAST

Set maxfast to value. The algorithm allocates all blocks below the size of maxfast in large groups and then doles them out very quickly. The default value for maxfast is 24.

M_NLBLKS

Set numlblks to value. The above mentioned ‘‘large groups’’ each contain numlblks blocks. numlblks must be greater than 0. The default value for numlblks is 100.

M_GRAIN

Set grain to value. The sizes of all blocks smaller than maxfast are considered to be rounded up to the nearest multiple of grain. grain must be greater than 0. The default value of grain is the smallest number of bytes that will allow alignment of any data type. Value will be rounded up to a multiple of the default when grain is set.

M_KEEP

Preserve data in a freed block until the next malloc(), realloc(), or calloc(). This option is provided only for compatibility with the old version of malloc() and is not recommended.

These values are defined in the <malloc.h> header.

mallopt() may be called repeatedly, but may not be called after the first small block is allocated.

mallinfo() provides instrumentation describing space usage. It returns the mallinfo structure with the following members:

."struct mallinfo {

int	arena;	/* total space in arena */
int	ordblks;	/* number of ordinary blocks */
int	smblks;	/* number of small blocks */
int	hblkhd;	/* space in holding block headers */
int	hblks;	/* number of holding blocks */
int	usmblks;	/* space in small blocks in use */
int	fsmblks;	/* space in free small blocks */
int	uordblks;	/* space in ordinary blocks in use */
int	fordblks;	/* space in free ordinary blocks */
int	keepcost;	/* space penalty if keep option */
		/* is used */

."}

The mallinfo structure is defined in the <malloc.h> header.

Each of the allocation routines returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object.

Return Values

Errors

ENOMEM

size bytes of memory exceeds the physical limits of your system, and cannot be allocated.

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.

See Also

Notes

Note that unlike malloc(3C) , this package does not preserve the contents of a block when it is freed, unless the M_KEEP option of mallopt() is used.

Undocumented features of malloc(3C) have not been duplicated.

Function prototypes for malloc(), realloc(), calloc(), and free() are also defined in the <malloc.h> header for compatibility with old applications. New applications should include <stdlib.h> to access the prototypes for these functions.
Comparative Features of malloc(3X) , bsdmalloc(3X) , and malloc(3C) :

• These malloc(3X) routines are space-efficient, but have slower performance.
• The bsdmalloc(3X) routines afford better performance, but are space-inefficient.
• The standard, fully SCD-compliant malloc(3C) routines are a trade-off between performance and space-efficiency.

free() does not set errno.

Table of Contents

• Name
• Synopsis
• MT-Level
• Description
• Return Values
• Errors
• See Also
• Notes