Hard to produce error conditions

Now take a look at the function putdata().

                   void
                   putdata(output, data)
                   char    data;
                   FILE    output;
          [9]      {
                       / check for file system out of space /
         [11]          if (fprintf(output, "%s", data) < 0) {
     [U] [12]              fprintf(stderr, "write error with file '%s'", filename);
     [U] [13]              fclose(output);
     [U] [14]              unlink(newreffile);
     [U] [15]              exit(1);
                       }
         [17]      }

Output from lprof -x for putdata()

Because this error is hard to produce, the error recovery part of the function usually does not get tested. You can simulate the error, however, by writing your own fprintf() function that returns a value less than 0. That will cause the error recovery part of the function to be exercised, allowing you to see the following error message:

   write error with file '@%#&HP'