alloca(3C)

NAME
     alloca - Allocates dynamic space

SYNOPSIS
     #include <alloca.h>

     void *alloca (unsigned size);

DESCRIPTION
     alloca returns a pointer to size bytes of uninitialized local stack
     space.  Because the space is allocated using a built-in compiler
     function, the allocation is quite fast.  If zero is passed as size,
     alloca returns a valid pointer (unlike some versions of malloc, which
     consider a zero size to be an error).

     The #include <alloca.h> is required.

     Space allocated when a function foo calls alloca is freed
     automatically when foo returns.

     It is an error to call free with a pointer returned by alloca.

     Not all environments have alloca in their libraries, so code using it
     is not necessarily portable.  Reasonably portable public domain
     versions of this function are available from various sources on the
     Internet and the World Wide Web.

FILES
     /usr/include/alloca.h

DIAGNOSTICS
     In this implementation, alloca cannot fail (although if size makes the
     process too large IRIX may kill the process).  Because alloca always
     returns a valid pointer, no diagnostics are possible.  Portability may
     be enhanced if the function calling alloca tests for a return value of
     0 and handles 0 as an error.

CAVEATS
     Do not call alloca as an argument to another function, as in
     foo(alloca(20));.  Use the following example instead:

          cp = alloca(20); foo(cp);

SEE ALSO
     malloc(3), calloc(3), free(3)