Debugging with GDB

The GNU Debugger (GDB) is a powerful tool for finding and fixing bugs in C programs.

In this lesson, you will learn:

• How to compile programs for debugging.
• How to set breakpoints and inspect variables.
• How to step through code execution.

Compiling a Program for Debugging

To use GDB, compile your program with the -g flag:

gcc -g program.c -o program

This includes debugging information in the executable.

Starting GDB

To run a program in GDB:

gdb ./program

Once inside GDB, you can set breakpoints and inspect the program's execution.

Setting Breakpoints

A breakpoint stops the program at a specific line, allowing you to inspect variables and execution.

To set a breakpoint:

break main

This stops execution at the beginning of the main() function.

Example: Using GDB to Debug a Program

This program contains a bug that we will debug using GDB.

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("You entered: %d\n", num);
    return 0;
}

Running the Program in GDB

After setting a breakpoint, run the program using:

run

The program stops at the breakpoint, allowing you to inspect variables.

Inspecting Variables

Use the print command to check variable values:

print num

This helps identify incorrect values during execution.

Stepping Through Code

Use next to execute the next line of code.

Use step to enter function calls for deeper inspection.

Summary

In this lesson, you learned:

• How to compile and run a program in GDB.
• How to set breakpoints and inspect variables.
• How to step through code execution.

Next, we will explore common runtime errors in C!