c - To use goto or not?

Question

This question may sound cliched, but I am in a situation here.

I am trying to implement a finite state automaton to parse a certain string in C. As I started writing the code, I realised the code may be more readable if I used labels to mark the different states and use goto to jump from one state to another as the case comes.

Using the standard breaks and flag variables is quite cumbersome in this case and hard to keep track of the state.

What approach is better? More than anything else I am worried it may leave a bad impression on my boss, as I am on an internship.

Answer 1

There is nothing inherently wrong with goto. The reason they are often considered "taboo" is because of the way that some programmers (often coming from the assembly world) use them to create "spaghetti" code that is nearly impossible to understand. If you can use goto statements while keeping your code clean, readable, and bug-free, then more power to you.

Using goto statements and a section of code for each state is definitely one way of writing a state machine. The other method is to create a variable that will hold the current state and to use a switch statement (or similar) to select which code block to execute based on the value of the state variable. See Aidan Cully's answer for a good template using this second method.

In reality, the two methods are very similar. If you write a state machine using the state variable method and compile it, the generated assembly may very well resemble code written using the goto method (depending on your compiler's level of optimization). The goto method can be seen as optimizing out the extra variable and loop from the state variable method. Which method you use is a matter of personal choice, and as long as you are producing working, readable code I would hope that your boss wouldn't think any different of you for using one method over the other.

If you are adding this code to an existing code base which already contains state machines, I would recommend that you follow whichever convention is already in use.