DynamicAllocation.c

#include "apue.h" 
#include < errno.h> 
#include < limits.h>
#ifdef PATH_MAX
static long pathmax = PATH_MAX;
#else static long pathmax = 0;
#endif static long posix_version = 0;
static long xsi_version = 0;
/* If PATH_MAX is indeterminate, no guarantee this is adequate */ 
#define PATH_MAX_GUESS 1024 char *
path_alloc(size_t *sizep) /* also return allocated size, if nonnull */
{
    char *ptr;
    size_t size;
    if (posix_version == 0)
        posix_version = sysconf(_SC_VERSION);
    if (xsi_version == 0)
        xsi_version = sysconf(_SC_XOPEN_VERSION);
    if (pathmax == 0)
    { /* first time through */
        errno = 0;
        if ((pathmax = pathconf("/", _PC_PATH_MAX)) < 0)
        {
            if (errno == 0)
                else
        }
        else
        {
            pathmax++;
        }
    } /*
*Before POSIX.1-2001, we aren’t guaranteed that PATH_MAX includes *the terminating null byte. Same goes for XPG3. */
    if ((posix_version < 200112L) && (xsi_version < 4))
        size = pathmax + 1;
    else
        size = pathmax;
    if ((ptr = malloc(size)) == NULL)
        err_sys("malloc error for pathname");
    if (sizep != NULL)
        *sizep = size;
    return (ptr);
}