Using a debugger

How to:

GDB (GNU Debugger) is the most commonly used debugger for C programming. Here is a brief guide on using GDB to debug a simple C program.

First, compile your C program with the -g flag to include debugging information:

gcc -g program.c -o program

Next, start GDB with your compiled program:

gdb ./program

You can now use various commands within GDB to control its operation. Here are a few fundamental commands:

  • break: Set a breakpoint at a specified line or function to pause execution.
    • Example: break 10 or break main
  • run: Start the execution of your program within GDB.
  • next: Execute the next line of code without stepping into functions.
  • step: Execute the next line of code, stepping into functions.
  • print: Display the value of a variable.
  • continue: Resume execution until the next breakpoint.
  • quit: Exit GDB.

Here’s an example session debugging a simple program:

#include <stdio.h>

int main() {
    int i;
    for (i = 0; i < 5; i++) {
        printf("%d\n", i);
    return 0;

Compile and start GDB as described. Set a breakpoint at the printf line with break 5 and then run. Use next to step through the loop and print i to inspect the loop variable.

Sample output after setting a breakpoint and before the first iteration:

Breakpoint 1, main () at program.c:5
5         printf("%d\n", i);

Using print i after a few iterations:

$3 = 2

This demonstrates examining the state and flow of a simple program.

Deep Dive

The concept of debugging has evolved significantly since the early days of programming, where physical bugs (literal insects) could cause issues in mechanical computers. Today, debuggers like GDB offer sophisticated features beyond basic stepping and variable inspection, such as reverse debugging (executing the program backward), conditional breakpoints, and scripting for automated debugging tasks.

While GDB is powerful and widely used, it can be dense and challenging for beginners. Alternative debugging tools and IDEs (Integrated Development Environments) such as Visual Studio Code, CLion, or Eclipse offer more user-friendly interfaces for debugging C code, often integrating visual aids and more intuitive controls. These alternatives might not offer GDB’s full depth of functionality but can be more accessible to newcomers to C programming.

Moreover, the emergence of language server protocols and debugging standards has facilitated cross-platform debugging solutions, making the debugging experience more consistent across different tools and environments. Despite these advancements, learning the ins and outs of a traditional debugger like GDB provides invaluable insight into the execution of C programs and remains a crucial skill in a developer’s toolkit.