C language: 12. GDB tool debugging C program

1、 brief introduction

GDB The tool is in linux A debugging tool used when programming in the environment , Powerful , Easy to use , It is a sharp tool for program debugging .

DB Commissioning conditions ：
about GDB Program files for debugging , You need to add -g Options , Only the generated executable can be used GDB Conduct source level debugging . among -g Option is to add source code information to the executable , At the same time, it must be ensured that GDB Can find the source code file . Therefore, the source code file cannot be deleted

2、gdb Debugging example

1、 establish /main.c

#include <stdio.h>
void change(int *a, int *b)
{
    
        int tmp = *a;
        *a=*b;
        *b=tmp;
}
int main()
{
    
        int a=5;
        int b=3;
        change(&a, &b);

        printf("num a=%d\nnum b=%d\n", a, b);
        return 0;
}

2、 compile /main.c

gcc -g main.c -o main.out

3、 establish main2.c

#include <stdio.h>
void change(int a, int b)
{
    
        int tmp = a;
        a=b;
        b=tmp;
}
int main()
{
    
        int a=5;
        int b=3;
        change(a, b);

        printf("num a=%d\nnum b=%d\n", a, b);
        return 0;
}

4、 compile main2.c

gcc -g main2.c -o main2.out

5、 Start debugging

gdb main2.out

6、 List the source code of the current software project

Use l Command to view the source code ;
l The order is list An abbreviation for a command , Therefore use l Command effect and list Orders are equal to ;

7、 Carry on

Press enter , It means to continue to execute the command of the previous step

8、 Start debugging

Use command start Start debugging ,
start The command says ： Start debugging , Stop at the first line of code

9、 Print variables

Use command p Print variables ;
p The order is print An abbreviation for a command ;

10、 Debug the next line

Use command n Execute the next line of code ;
n The order is next An abbreviation for a command ;

11、 Enter the function and execute

perform s command ;
s：step Execute a line of source code , If there is a function call in this line of code , Enter the function ;

12、 Look at the function stack

Carry out orders bt

13、 Switch stack

Carry out orders f 1

14、 Exit debugging

Use command q

3、GDB Debug pointer

Prove that memory is continuous

1、 establish /main.c

#include <stdio.h>
void change(int *a, int *b)
{
    
        int tmp = *a;
        *a=*b;
        *b=tmp;
}
int main()
{
    
        int a=5;
        int b=3;
        change(&a, &b);

        printf("num a=%d\nnum b=%d\n", a, b);
        return 0;
}

2、 compile /main.c

gcc -g main.c -o main.out

3、 debugging main.out

gdb main.out