NAME

malloc, free, realloc, calloc, cfree, alloca − memory allocator

SYNOPSIS

char ∗malloc(size)
unsigned size;

free(ptr)
char ∗ptr;

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

char ∗calloc(nelem, elsize)
unsigned nelem, elsize;

cfree(ptr)
char ∗ptr;

char ∗alloca(size)
int size;

malloc_ok(size)
int 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.

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 a cartesian tree of free blocks.  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. 

Realloc also works if ptr points to a block freed since the last call of malloc, realloc or calloc.

Calloc allocates space for an array of nelem elements of size elsize.  The space is initialized to zeros, and can be freed with cfree. 

Alloca allocates size bytes of space in the stack frame of the caller.  This temporary space is automatically freed on return. 

Ocassionally a program will overun the storage allocated from Malloc .  Malloc_ok helps determine when this has happened.  It checks all blocks (free or allocated) looking for duplicates, strange addresses and absurd sizes.  Malloc_ok returns true if everything is is found.  The size parameter specifies the maximum acceptable size of a block.  A block with a larger size is considered bad.  If size is zero a maximum of 10000 is assumed. 

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

Fast Fits by C. J. Stephenson

DIAGNOSTICS

Malloc, realloc and calloc return a null pointer (0) if there is no available memory or if the arena has been detectably corrupted by storing outside the bounds of a block. 

BUGS

When realloc returns 0, the block pointed to by ptr may be destroyed. 

Alloca is machine dependent; it’s use is discouraged. 

Sun Release 1.1  —  Last change: 21 March 1984