要调试生成的可执行程序，必须在生成的时候加入-g选项，生成可以调试的代码
例如：gcc -o test a.c b.c -g
这样gcc就会在链接的时候加入一些用于调试的符号
在生成可以调试的可执行程序后，使用gdb命令进入调试模式
1 root@ubuntu:/home/leo/test/project/classes# gdb test
2 GNU gdb (Ubuntu 7.10-1ubuntu2) 7.10
3 Copyright (C) 2015 Free Software Foundation, Inc.
4 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
5 This is free software: you are free to change and redistribute it.
6 There is NO WARRANTY, to the extent permitted by law. Type "show copying"
7 and "show warranty" for details.
8 This GDB was configured as "x86_64-linux-gnu".
9 Type "show configuration" for configuration details.
10 For bug reporting instructions, please see:
11 <http://www.gnu.org/software/gdb/bugs/>.
12 Find the GDB manual and other documentation resources online at:
13 <http://www.gnu.org/software/gdb/documentation/>.
14 For help, type "help".
15 Type "apropos word" to search for commands related to "word"...
16 Reading symbols from test...done.
17 (gdb)
此时，程序并没有开始运行，在运行程序之前，可以做一些准备工作
1. 设置运行参数
(gdb) set args 5 设置第一个参数为5
(gdb) show args
Argument list to give program being debugged when it is started is "5".
2. 设置断点，break命令，简写b
在指定行数设置断点
(gdb) b 8 在第8行设置断点
Breakpoint 1 at 0x4004f0: file main.cpp, line 8.
(gdb)
为指定函数设置断点
(gdb) b add_int Breakpoint 3 at 0x400660: file math/add_int.cpp, line 5.
在指定行数或函数设置条件变量
(gdb) b add_int if num1 == 1
Breakpoint 4 at 0x400660: file math/add_int.cpp, line 5.
查看断点
(gdb) info breakpoints Num Type Disp Enb Address What 4 breakpoint keep y 0x0000000000400660 in add_int(int, int) at math/add_int.cpp:5 stop only if num1 == 1 breakpoint already hit 1 time
禁用断点 disable b 4，禁用4号断点
启动断点 enable b 4，启用4号断点
删除断点 clear 51 删除51行的断点
3. 查看源文件，list命令，简写l
(gdb) list
1 #include "stdlib.h"
2 #include "stdio.h"
3
4 int add_int(int, int);
5 float add_float(float, float);
6
7 int main(int argc, char *argv[])
8 {
9 int value = (*argv[1]) - '0';
10 printf("Leo is here %d . \n", value);
(gdb) list
11
12 int num1 = add_int(1, 2);
13 float num2 = add_float(2.3, 4.5);
14 printf("result is %d %f.", num1, num2);
15
16 getchar();
17
18 return 0;
19 }
(gdb) list
Line number 20 out of range; main.cpp has 19 lines.
(gdb)
也可以指定查看的行数list 5,,10，查看从5到10行的源代码
做好准备工作之后，就可以真正运行程序了
4. 运行程序，run命令，简写r
(gdb) b 8
Breakpoint 1 at 0x4004f0: file main.cpp, line 8.
(gdb) run 5 可以直接在run后面可以跟运行参数，也可以用set设置运行参数
Starting program: /home/leo/test/project/classes/test 5
Breakpoint 1, main (argc=2, argv=0x7fffffffe018) at main.cpp:8
8 {
(gdb)
5. 查看变量，display命令。在使用断点命令后，在运行到断点处，就可以使用此命令查看变量得值了
(gdb) b 8
Breakpoint 1 at 0x4004f0: file main.cpp, line 8.
(gdb) run 5
Starting program: /home/leo/test/project/classes/test 5
Breakpoint 1, main (argc=2, argv=0x7fffffffe018) at main.cpp:8
8 {
(gdb) display argc 查看运行参数个数
1: argc = 2
(gdb) display argv[1] 查看第一个运行参数的值
2: argv[1] = 0x7fffffffe38b "5"
(gdb)
6. 继续执行，continue命令，简写c
(gdb) b 8
Breakpoint 1 at 0x4004f0: file main.cpp, line 8.
(gdb) run 5
Starting program: /home/leo/test/project/classes/test 5
Breakpoint 1, main (argc=2, argv=0x7fffffffe018) at main.cpp:8
8 {
(gdb) c
Continuing.
Leo is here 5 .
result is 3 6.800000.
[Inferior 1 (process 4009) exited normally]
7. 修改变量的值，set命令
(gdb) b 8
Breakpoint 1 at 0x4004f0: file main.cpp, line 8.
(gdb) run 7
Starting program: /home/leo/test/project/classes/test 7
Breakpoint 1, main (argc=2, argv=0x7fffffffe018) at main.cpp:8
8 {
(gdb) display argv[1]
1: argv[1] = 0x7fffffffe38b "7"
(gdb) set argv[1] = "8" 将第一个运行参数的值从字符串“7”改为“8”
(gdb) c
Continuing.
Leo is here 8 .
result is 3 6.800000.
[Inferior 1 (process 4009) exited normally]
8. 退出调试，q命令
(gdb) q
A debugging session is active.
Inferior 1 [process 3997] will be killed.
Quit anyway? (y or n) y
9. 查看变量类型，whatis命令
(gdb) whatis num1
type = int
(gdb)
10. 查看结构详细定义，ptype命令
(gdb) ptype u
type = struct User {
int id
char name[20]
}
10. 进入函数体（step，简写s）和单步调试命令（next，简写n）
(gdb) s
6 }2: num2 = 2
1: num1 = 1
(gdb) n
main (argc=<optimized out>, argv=<optimized out>) at main.cpp:13
13 float num2 = add_float(2.3, 4.5);
(gdb)
11. 查看调用堆栈（backtrace，简写bt）
(gdb) bt
#0 add_int (num1=num1@entry=1, num2=num2@entry=2) at math/add_int.cpp:6
#1 0x000000000040051b in main (argc=<optimized out>, argv=<optimized out>)
at main.cpp:12
(gdb)
12. 获取当前断点下的运行情况（info）
13. 多线程调试
info thread: 获取当前进程中所有线程信息；
thread thread_id: 进入指定的线程进行调试；
14. 打印指定函数的汇编代码
disassamble sum
15. 帮助信息
help
