(libc.info)Malloc Examples


Examples of `malloc'
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   If no more space is available, `malloc' returns a null pointer.  You
should check the value of _every_ call to `malloc'.  It is useful to
write a subroutine that calls `malloc' and reports an error if the
value is a null pointer, returning only if the value is nonzero.  This
function is conventionally called `xmalloc'.  Here it is:

     void *
     xmalloc (size_t size)
     {
       register void *value = malloc (size);
       if (value == 0)
         fatal ("virtual memory exhausted");
       return value;
     }

   Here is a real example of using `malloc' (by way of `xmalloc').  The
function `savestring' will copy a sequence of characters into a newly
allocated null-terminated string:

     char *
     savestring (const char *ptr, size_t len)
     {
       register char *value = (char *) xmalloc (len + 1);
       value[len] = '\0';
       return (char *) memcpy (value, ptr, len);
     }

   The block that `malloc' gives you is guaranteed to be aligned so
that it can hold any type of data.  In the GNU system, the address is
always a multiple of eight on most systems, and a multiple of 16 on
64-bit systems.  Only rarely is any higher boundary (such as a page
boundary) necessary; for those cases, use `memalign', `posix_memalign'
or `valloc' (Note: Aligned Memory Blocks).

   Note that the memory located after the end of the block is likely to
be in use for something else; perhaps a block already allocated by
another call to `malloc'.  If you attempt to treat the block as longer
than you asked for it to be, you are liable to destroy the data that
`malloc' uses to keep track of its blocks, or you may destroy the
contents of another block.  If you have already allocated a block and
discover you want it to be bigger, use `realloc' (Note: Changing Block
Size).


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