malloc.3c (2010 09)

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malloc(3C) malloc(3C)

NAME

malloc(), alloca(), calloc(), free(), mallinfo(), mallopt(), memorymap(), realloc(), valloc() - main memory

allocator

SYNOPSIS

#include <stdlib.h>

void *malloc(size_t size);

void *calloc(size_t nelem, size_t elsize);

void free(void *ptr);

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

void *valloc(size_t size);

void memorymap(int show_stats);

(Obsoleted)

alloca()

#include <alloca.h>

void *alloca(size_t size);

System V Synopsis

#include <malloc.h>

char *malloc(unsigned size);

char *calloc(unsigned nelem, unsigned elsize);

void free(char *ptr);

int mallopt(int cmd, int value);

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

struct mallinfo mallinfo(void);

Remarks

The functionality in the old

malloc() package has been incorporated into malloc(). The library

(

/usr/lib/libmalloc.a

) corresponding to the -lmalloc linker option is now an empty library on

PA-RISC based systems only; it does not exist on Itanium-based systems. Makeﬁles that reference this

library on PA-RISC based systems will continue to work, but they will not work on Itanium-based sys-

tems.

Obsolescent Interfaces

memorymap() has been deprecated at HP-UX 11i Version 1 and is now obsolete. The

mal-

linfo() function is more useful for malloc statistics.

DESCRIPTION

The functions described here provide a simple, general purpose memory allocation package:

malloc() Allocates space for a block of at least size bytes, but does not initialize the space.

calloc() Allocates space for an array of nelem elements, each of size elsize bytes, and initial-

izes the space to zeros. Actual amount of space allocated will be at least nelem *

elsize bytes.

realloc() Changes the size of the block pointed to by ptr to size bytes and returns a pointer to

the (possibly moved) block. Existing 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 and NULL is returned. realloc() of blocks with special align-

ments, such as those created by valloc(), is not supported.

valloc() Allocates space for a block of at least size bytes starting on a boundary aligned to a

multiple of the value returned by sysconf(__SC_PAGESIZE). This space is unin-

itialized.

free() Deallocates the space pointed to by ptr (a pointer to a block previously allocated by

malloc(), realloc(), calloc(),orvalloc()) and makes the space

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (6 pages)

PAGE 1
malloc(3C) malloc(3C) NAME malloc(), alloca(), calloc(), free(), mallinfo(), mallopt(), memorymap(), realloc(), valloc() - main memory allocator SYNOPSIS #include void *malloc(size_t size); void *calloc(size_t nelem, size_t elsize); void free(void *ptr); void *realloc(void *ptr, size_t size); void *valloc(size_t size); void memorymap(int show_stats); (Obsoleted) alloca() #include void *alloca(size_t size); System V Synopsis #include
PAGE 2
malloc(3C) malloc(3C) available for further allocation. If ptr is a NULL pointer, no action occurs. mallopt() Provides for control over the allocation algorithm and other options in the mal- loc() package. 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, then doles them out very quickly. The default value for maxfast is zero. M_NLBLKS Set numlblks to value .
PAGE 3
malloc(3C) malloc(3C) memorymap() Displays the contents of the memory allocator for HP-UX 32-bit operating systems only. A list of addresses and block descriptions is written (using printf()) to standard output. If the value of the show_stats parameter is 1, statistics concerning number of blocks and sizes used will also be written. If the value is zero, only the memory map will be written. The addresses and sizes displayed by memorymap() may not correspond to those requested by an application.
PAGE 4
malloc(3C) malloc(3C) Here is an example of how to use _M_ARENA_OPTS, $ export _M_ARENA_OPTS = 16:8 This means that the number of arenas is 16, and the expansion size is 8*4096 bytes. In general, the more arenas you use, the smaller the expansion factor should be, and vice versa. _M_SBA_OPTS is used to turn on the small block allocator, and to set up parameters for the small block allocator, namely, maxfast , grain , and numlblks .
PAGE 5
malloc(3C) malloc(3C) max_cache_misses enables cached blocks to be exchanged among threads. A thread that heavily allocates blocks of a certain size is soon bound to run out of blocks in its private cache. The exchange allows the thread to borrow blocks from a global pool if available. This may be more efficient than going back to the arena.
PAGE 6
malloc(3C) malloc(3C) STANDARDS CONFORMANCE malloc(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C calloc(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C free(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C mallinfo(): SVID2, XPG2 mallopt(): SVID2, SVID3, XPG2 realloc(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.