malloc man page on Ultrix

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malloc(3x)							    malloc(3x)

       malloc,	free,  realloc,	 calloc,  mallopt, mallinfo - fast main memory

       #include <malloc.h>

       char ∗malloc (size)
       unsigned size;

       void free (ptr)
       char ∗ptr;

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

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

       int mallopt (cmd, value)
       int cmd, value;

       struct mallinfo mallinfo (max)
       int max;

       The and subroutines provide a simple general-purpose memory  allocation
       package,	 which runs considerably faster than the package.  It is found
       in the library and is loaded if the option is used with or

       The subroutine returns a pointer to a block  of	at  least  size	 bytes
       suitably aligned for any use.

       The  argument  to is a pointer to a block previously allocated by After
       is performed, this space is made available for further allocation,  and
       its  contents  have been destroyed.  See below for a way to change this

       Undefined results will occur if the space assigned by is overrun or  if
       some random number is handed to

       The  subroutine changes the size of the block pointed to by ptr to size
       bytes and returns a pointer to the (possibly moved)  block.   The  con‐
       tents will be unchanged up to the lesser of the new and old sizes.

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

       The subroutine 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 0.

       M_NLBLKS Set numlblks to value .	 The above mentioned large groups each
		contain numlblks blocks.  The 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	multi‐
		ple of grain .	The 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 or  This	option
		is provided only for compatibility with the old version of and
		is not recommended.

       These values are defined in the malloc.h header file.

       The subroutine may be called repeatedly, but may not  be	 called	 after
       the first small block is allocated.

       The subroutine provides information describing space usage.  It returns
       the following 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

       This package usually uses more data space than
       The code size is also bigger than
       Note that unlike this package does not preserve the contents of a block
       when it is freed, unless the M_KEEP option of is used.
       Undocumented features of have not been duplicated.

Return Values
       The and subroutines return a NULL pointer if there is not enough avail‐
       able memory.  When returns NULL, the block pointed to by	 ptr  is  left
       intact.	 If  is	 called	 after	any  allocation or if cmd or value are
       invalid, nonzero is returned.  Otherwise, it returns zero.

See Also
       brk(2), malloc(3)


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