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GDB: GNU Debugger
GDB, or the GNU Project Debugger, is a powerful command-line debugger used primarily for C, C++, and other languages. It can help you find runtime errors, examine the program's execution state, and manipulate the flow to detect and fix bugs easily.
Getting started with GDB
To start using GDB, you first need to compile your code with the -g flag, which includes debugging information in the executable:
g++ -g myfile.cpp -o myfile
Now, you can load your compiled program into GDB:
gdb myfile
Basic GDB Commands
Here are some common GDB commands you'll find useful when debugging:
run: Start your program.break [function/line number]: Set a breakpoint at the specified function or line.continue: Continue the program execution after stopping on a breakpoint.next: Execute the next line of code, stepping over function calls.step: Execute the next line of code, entering function calls.print [expression]: Evaluate an expression in the current context and display its value.backtrace: Show the current call stack.frame [frame-number]: Switch to a different stack frame.quit: Exit GDB.
Example Usage
Suppose you have a simple cpp file called example.cpp:
#include <iostream>
void my_function(int i) {
std::cout << "In my_function with i = " << i << std::endl;
}
int main() {
for (int i = 0; i < 5; ++i) {
my_function(i);
}
return 0;
}
First, compile the code with debugging symbols:
g++ -g example.cpp -o example
Start GDB and load the example program:
gdb example
Set a breakpoint in the my_function function and run the program:
(gdb) break my_function
(gdb) run
Once stopped at the breakpoint, use next, print, and continue to examine the program's state:
(gdb) next
(gdb) print i
(gdb) continue
Finally, exit GDB with the quit command.
This was just a brief summary of GDB; you can find more details in the official GDB manual.