Lesson 59: Debugging Techniques and Tools
Debugging is the process of finding and fixing errors (bugs) in software. C programs can suffer from three main types of errors:
- Syntax Errors: Caught by the compiler (e.g., missing semicolon).
- Linker Errors: Occur when combining object files (e.g., calling a function that was declared but never defined).
- Logical/Runtime Errors: The program runs but behaves incorrectly (e.g., array bounds violations, infinite loops, memory leaks). These require a debugger.
Essential Techniques
- Print Statements: The simplest debugging method. Insert
printf()statements to track variable values and execution flow. - Isolation: Comment out sections of code to pinpoint where the error originates.
- Incremental Development: Write and test small chunks of code rather than writing the whole program at once.
Using a Debugger (GDB: GNU Debugger)
A debugger allows you to execute your program step-by-step, inspect variable states, and control flow.
1. Compilation with Debug Info
To use GDB, compile your code with the -g flag:
bash gcc program.c -o program -g
2. Basic GDB Commands (Conceptual)
| Command | Description |
|---|---|
gdb ./program | Start the debugger with the executable |
break main | Set a breakpoint at the start of main |
run | Start execution (stops at the breakpoint) |
next | Execute the next line, skipping function calls |
step | Execute the next line, entering function calls |
print variable | Display the current value of a variable |
continue | Continue execution until the next breakpoint |
quit | Exit GDB |
Mastering a debugger is essential for finding difficult, intermittent bugs, especially those involving pointers and memory.