#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

int main()
{
   char filename[] = "TemporaryXXXXXX";

   int fd = mkstemp(filename);
   close(fd);

   printf("filename = %s\n", filename);

   /* ... */

   return 0;
}

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

/* Create a file with an unique name, beginning with the specified prefix.
 *
 * The file name will be dynamically allocated, and saved in the pointer
 * pointed by nameptr. After you are done with the file, you should
 * release the dynamically allocated name using free().
 *
 * If you supply NULL nameptr, the file will be immediately unlinked,
 * and the dynamically allocated file name freed. Thus, the file will not
 * have a name (except for a brief moment within this function).
 * (In this case, the function is similar to tmpfile(), except that this
 *  function lets you specify the prefix or directory for the file.)
 *
 * If an error occurs, the function will return NULL with errno set.
 *
 * Example:
 *
 *	FILE *filehandle;
 *	char *filename;
 *
 *	filehandle = fopen_unique("/tmp/my-prefix.", &filename);
 *	if (!filehandle) {
 *
 *		error, check errno [/I]for reason[/I]
 *
 *	} else {
 *
 *		work on the file
 *
 *		fclose(filehandle);
 *		remove(filename);
 *		free(filename);
 *	}
*/
FILE *fopen_unique(char const *const prefix, char **nameptr)
{
	size_t const	 n = (prefix) ? strlen(prefix) : 0;
	char		*name;
	FILE		*handle;
	int		 descriptor, result, saved_errno;

	if (n < (size_t)1) {
		errno = EINVAL;
		return NULL;
	}

	name = malloc(n + 7);
	if (!name) {
		errno = ENOMEM;
		return NULL;
	}
	memcpy(name, prefix, n);
	name[n+0] = 'X';
	name[n+1] = 'X';
	name[n+2] = 'X';
	name[n+3] = 'X';
	name[n+4] = 'X';
	name[n+5] = 'X';
	name[n+6] = 0;

	do {
		descriptor = mkstemp(name);
	} while (descriptor == -1 && errno == EINTR);
	if (descriptor == -1) {
		saved_errno = errno;
		free(name);
		errno = saved_errno;
		return NULL;
	}

	if (!nameptr) {
		do {
			result = unlink(name);
		} while (result == -1 && errno == EINTR);
		if (result == -1) {
			saved_errno = errno;
			close(descriptor);
			free(name);
			errno = saved_errno;
			return NULL;
		}
		free(name);
		name = NULL;
	} else {
		*nameptr = name;
	}

	do {
		handle = fdopen(descriptor, "r+");
	} while (handle == NULL && errno == EINTR);
	if (!handle) {
		saved_errno = errno;
		if (name) {
			unlink(name);
			free(name);
		}
		close(descriptor);
		errno = saved_errno;
		return NULL;
	}

	return handle;
}