Debugging tool under Linux-GDB

GDB

1.What is GDB

GDB is a debugging tool provided by the GNU software system community. Together with GCC, it forms a complete development environment. GDB is the standard development environment for Linux and many Unix-like systems.

Generally speaking, GDB can mainly provide help in the following four aspects:

Start the program and run it as you like according to customized requirements;
The debugged program can be stopped at the specified breakpoint (The breakpoint can also be a conditional expression);
When the program is stopped, you can check the status of variables in the current program;
You can modify the program to correct the impact of one BUG to test other BUGs;

2. Preparation

Usually, when compiling for debugging, we need to turn off the optimization option -O and turn on the debugging option -g.

In addition, -Wall will choose to turn on all warning without affecting the program behavior as much as possible. It can also find many problems and avoid unnecessary BUGs.

gcc -g -Wall program.c -o program

The -g option is used to add source code information to the executable file, such as which machine instruction in the executable file corresponds to which line of source code. But it does not add the entire The source file is embedded in the executable file, so you must ensure that GDB can find the source filewhen debugging.

3.GDB commands – start, exit, view code

Test using the following files:

main.c

#include <stdio.h>
#include <stdlib.h>

#include "head.h"

int main(int argc,char* argv[]){<!-- -->

    int a , b;
    if(argc < 3){<!-- -->
        a = 10, b = 20;
    }
    else{<!-- -->
        a = atoi(argv[1]);
        b = atoi(argv[2]);
    }

    printf("a = %d , b = %d\\
",a,b);
    printf("a + b = %d\\
",add(a,b));
    printf("a - b = %d\\
",sub(a,b));
    printf("a * b = %d\\
",mul(a,b));
    printf("a / b = %.2lf\\
",divide(a,b));
    printf("xixixixixixi\\
");

    printf("hello makefile\\
");


    for(int i = 0;i < 20;i + + ){<!-- -->
        printf("%d ",i + 1);
    }
    printf("\\
");

    return 0;
}

head.h

#include <stdio.h>

int add(int a,int b);

int sub(int a,int b);

int mul(int a,int b);

double divide(int a,int b);

add.c

#include "head.h"

int add(int a,int b){<!-- -->
    return a + b;
}

sub.c

#include "head.h"

int sub(int a,int b){<!-- -->
    return a - b;
}

mul.c

#include "head.h"

int mul(int a,int b){<!-- -->
    return a * b;
}

div.c

#include "head.h"

double divide(int a,int b){<!-- -->
    return a * 1.0 / b;
}

Makefile

src=$(wildcard *.c)
objs=$(patsubst %.c,%.o,$(src))

target=app

$(target):$(src)
$(CC) $(src) -o $(target) -g


.PHONY:clean
clean:
rm $(objs) -f

1. Start and exit

gdb executable file;
quit / q;

First use make to generate an executable program app with debugging information, and then use gdb to start and exit.

2. Set parameters/get parameters for the program

set args 10 20 ...;
show args;

3.GDB usage help

help;

4. View the current file code

list / l (displayed from default position);
list / l line number (displayed starting from the specified line, with the specified line number in the middle);
list/l function name (displayed from the specified function);

The default is to display from the starting position.