How to create a temporary text file in C++?

Here’s a complete example:

#include <unistd.h>

int main(void) {
  char filename[] = "/tmp/mytemp.XXXXXX"; // template for our file.        
  int fd = mkstemp(filename);    // Creates and opens a new temp file r/w.
                                 // Xs are replaced with a unique number.
  if (fd == -1) return 1;        // Check we managed to open the file.
  write(fd, "abc", 4);           // note 4 bytes total: abc terminating '\0'
  /* ...
     do whatever else you want.
     ... */
  close(fd);
  unlink(filename);              // Delete the temporary file.
}

If you know the name of the file you want to create (and are sure it won’t already exist) then you can obviously just use open to open the file.

tmpnam and tmpfile should probably be avoided as they can suffer from race conditions – see man tmpfile(3) for the details.