GDB is a command line debugger. It is a good choice on Linux or WSL. On macOS, use LLDB instead.

1. sample.cpp

(base) yongqiang@yongqiang:~/workspace/yongqiang$ ls -l
total 4
-rwxr-xr-x 1 yongqiang yongqiang 365 Feb 16 22:52 sample.cpp
(base) yongqiang@yongqiang:~/workspace/yongqiang$

#include <iostream>
#include <vector>

double Sum(const std::vector<double> &data) {
	double total = 0;
	for (size_t i = 0; i < data.size(); ++i) {
		total += data[i];
	}

	return total;
}

int main() {
	std::vector<double> data;
	data.push_back(10);
	data.push_back(20);
	data.push_back(30);

	std::cout << "Sum(data) = " << Sum(data) << std::endl;

	return 0;
}

1.1. Compile and Run

(base) yongqiang@yongqiang:~/workspace/yongqiang$ uname -a
Linux yongqiang 5.15.167.4-microsoft-standard-WSL2 #1 SMP Tue Nov 5 00:21:55 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
(base) yongqiang@yongqiang:~/workspace/yongqiang$

Compile your program with the -g flag and start GDB in text user interface (TUI) mode.

(base) yongqiang@yongqiang:~/workspace/yongqiang$ ls -l
total 4
-rwxr-xr-x 1 yongqiang yongqiang 365 Feb 16 22:52 sample.cpp
(base) yongqiang@yongqiang:~/workspace/yongqiang$

(base) yongqiang@yongqiang:~/workspace/yongqiang$ g++ -g --std=c++17 sample.cpp -o sample
(base) yongqiang@yongqiang:~/workspace/yongqiang$ ls -l
total 144
-rwxr-xr-x 1 yongqiang yongqiang 142488 Feb 16 22:58 sample
-rwxr-xr-x 1 yongqiang yongqiang    365 Feb 16 22:52 sample.cpp
(base) yongqiang@yongqiang:~/workspace/yongqiang$

(base) yongqiang@yongqiang:~/workspace/yongqiang$ ./sample
Sum(data) = 60
(base) yongqiang@yongqiang:~/workspace/yongqiang$

2. GDB 调试

• Run program with GDB: $ gdb sample

• Set a breakpoint on main function: (gdb) break main or (gdb) b main

As breakpoing was set on main function, program will stop at main function and wait for gdb command.

• Run program: (gdb) run or (gdb) r

• Print value of total: (gdb) print total or (gdb) p total

(base) yongqiang@yongqiang:~/workspace/yongqiang$ gdb sample
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04.2) 9.2
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from sample...
(gdb) break main
Breakpoint 1 at 0x1314: file sample.cpp, line 13.
(gdb) run
Starting program: /home/yongqiang/workspace/yongqiang/sample

Breakpoint 1, main () at sample.cpp:13
13      int main() {
(gdb) list
8               }
9
10              return total;
11      }
12
13      int main() {
14              std::vector<double> data;
15              data.push_back(10);
16              data.push_back(20);
17              data.push_back(30);
(gdb) next
14              std::vector<double> data;
(gdb) next
15              data.push_back(10);
(gdb) next
16              data.push_back(20);
(gdb) next
17              data.push_back(30);
(gdb) break Sum
Breakpoint 2 at 0x5555555552a9: file sample.cpp, line 4.
(gdb) next
19              std::cout << "Sum(data) = " << Sum(data) << std::endl;
(gdb) next

Breakpoint 2, Sum (data=std::vector of length -840921094004155616, capacity -196785920380801129 = {...}) at sample.cpp:4
4       double Sum(const std::vector<double> &data) {
(gdb) next
5               double total = 0;
(gdb) print total
$1 = 6.9533558072559594e-310
(gdb) next
6               for (size_t i = 0; i < data.size(); ++i) {
(gdb) next
7                       total += data[i];
(gdb) next
6               for (size_t i = 0; i < data.size(); ++i) {
(gdb) next
7                       total += data[i];
(gdb) next
6               for (size_t i = 0; i < data.size(); ++i) {
(gdb) next
7                       total += data[i];
(gdb) next
6               for (size_t i = 0; i < data.size(); ++i) {
(gdb) next
10              return total;
(gdb) print total
$2 = 60
(gdb) next
11      }
(gdb) next
Sum(data) = 60
main () at sample.cpp:21
21              return 0;
(gdb) clear
No breakpoint at this line.
(gdb) quit
A debugging session is active.

        Inferior 1 [process 26162] will be killed.

Quit anyway? (y or n) y
(base) yongqiang@yongqiang:~/workspace/yongqiang$

3. GDB commands

Command	Description
run or r	Executes the program from start to end
break or b	Sets a breakpoint on a particular line
disable	Disables a breakpoint
enable	Enables a disabled breakpoint
next or n	Executes the next line of code without diving into functions; Step over functions
step	Goes to the next instruction, diving into the function; Step into functions
list or l	Displays the code
print or p	Displays the value of a variable
quit or q	Exits out of GDB
clear	Clears all breakpoints
continue or c	Continue execution until the next breakpoint

References

[1] Yongqiang Cheng, https://yongqiang.blog.csdn.net/
[2] GDB Tutorial, https://www.gdbtutorial.com/