Blog

When ever I get into a discussion about C with other developers I inevitably get asked “You don’t use goto statements do you?” For years I would answer “of course not! That’s bad practice!” Without really thinking of whether this answer was correct. Recently I have been realizing that it might simply not be the case.

Now don’t get me wrong, a goto is a tool that is very easy to misuse and abuse, and that is not what I am advocating at all! I am simply pointing out that there are times when using a goto in C provides a cleaner and easier to follow solution then any alternative.

C has no separate error handing code like C++ or Java. There is no try-catch or any other error specific statements. What C does have is goto. C allows you to give any line of code a name and jump to that line from anywhere in the same function. It acts as a one-way transfer of control. For error conditions, this can provide an excellent method to jump to some generic error handling code in your function (usually main()).

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

int main(int argc, char* argv[]){
   FILE *file = fopen(argv[1], "r");
   if (!file){
      goto error;
   }

   //Do something with the file here...

   fclose(file);
   return EXIT_SUCCESS;

error:
   fprintf(stderr, "An error occurred! %d (%s)\n", errno, strerror(errno));
   return errno;
}

In this example we try to open a file that is given as an argument to the program. If that file does not exist, or it cannot be opened for some reason we will jump to the error block. If the file is opened without any issue the program will continue on and exit normally. In this instance we are using the goto like a catch block.

$ ./test hello.txt
An error occurred! 2 (No such file or directory)

The overall lesson here is that goto blocks are not as evil as they are made out to be by modern programmers. There is a time and place for them, like any other tool. Just as you wouldn’t hang tile with a hammer and nails, you shouldn’t use goto statements for looping or general flow control.