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malloc(3) [minix man page]

MALLOC(3)						     Library Functions Manual							 MALLOC(3)

NAME
malloc, free, realloc, calloc, alloca - memory allocator SYNOPSIS
#include <sys/types.h> #include <stdlib.h> #include <alloca.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) void *alloca(size_t size) DESCRIPTION
Malloc and free provide a general-purpose memory allocation package. Malloc returns a pointer to a block of at least size bytes beginning on a word boundary. The argument to free is a pointer to a block previously allocated by malloc; this space is made available for further allocation, but its contents are left undisturbed. A call with a null ptr is legal and does nothing. Needless to say, grave disorder will result if the space assigned by malloc is overrun or if some random number is handed to free. Malloc maintains multiple lists of free blocks according to size, allocating space from the appropriate list. It calls sbrk (see brk(2)) to get more memory from the system when there is no suitable space already 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 will be unchanged up to the lesser of the new and old sizes. A call with a null ptr is legal and has the same result as malloc(size). Calloc allocates space for an array of nelem elements of size elsize. The space is initialized to zeros. Alloca allocates size bytes of space in the stack frame of the caller. This temporary space is automatically freed on return. 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). DIAGNOSTICS
Malloc, realloc and calloc return 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. NOTES
Other implementations of malloc, realloc or calloc may return a null pointer if the size of the requested block is zero. This implementa- tion will always return a zero length block at a unique address, but you should keep in mind that a null return is possible if the program is run to another system and that this should not be mistakenly seen as an error. BUGS
When realloc returns a null pointer, the block pointed to by ptr may be destroyed. Alloca is machine dependent; its use is discouraged. 4th Berkeley Distribution May 14, 1986 MALLOC(3)

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MALLOC(2)							System Calls Manual							 MALLOC(2)

NAME
malloc, free, realloc, calloc - memory allocator SYNOPSIS
#include <u.h> #include <libc.h> void* malloc(long size) void free(void *ptr) void* realloc(void *ptr, long size) void* calloc(long nelem, long elsize) DESCRIPTION
Malloc and free provide a simple memory allocation package. Malloc returns a pointer to a new block of at least size bytes. The block is suitably aligned for storage of any type of object. No two active pointers from malloc will have the same value. The argument to free is a pointer to a block previously allocated by malloc; this space is made available for further allocation. It is legal to free a null pointer; the effect is a no-op. 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 will be unchanged up to the lesser of the new and old sizes. The call realloc(0, size) means the same as Calloc allocates space for an array of nelem elements of size elsize. The space is initialized to zeros. Free frees such a block. Alef Except for calloc, these routines are available from Alef; they use the same arena as alloc. Malloc and realloc execute a check when they fail, rather than return nil. Memory returned by malloc is cleared. Realloc does not guarantee new memory is cleared unless ptr is nil. SOURCE
/sys/src/libc/port/malloc.c SEE ALSO
brk(2) DIAGNOSTICS
Malloc, realloc and calloc return 0 if there is no available memory. Errstr is likely to be set. BUGS
The different specification of calloc is bizarre. User errors can corrupt the storage arena. The most common gaffes are (1) freeing an already freed block, (2) storing beyond the bounds of an allocated block, and (3) freeing data that was not obtained from the allocator. When malloc and free detect such corruption, they abort. MALLOC(2)

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