NAME

malloc, free, realloc, calloc, mallopt, mallinfo − memory allocator

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)

DESCRIPTION

malloc and free provide a simple general-purpose memory allocation package. 

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, a system dependent value, is 24 on the M68000, and 96 on the M88000 family of processors.

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 which 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 file. 

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 structure:

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 ∗/
}

This structure is defined in the malloc.h header file. 

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

SEE ALSO

brk(2), malloc(3C). 

DIAGNOSTICS

malloc, realloc, and calloc return a NULL pointer if there is not enough available memory.  When realloc returns NULL, the block pointed to by ptr is left intact.  If mallopt is called after any allocation or if cmd or value are invalid, non-zero is returned.  Otherwise, it returns zero. 

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 file for compatibility with old applications. New applications should include <stdlib.h> to access the prototypes for these functions. 

  —  Specialized Libraries