gdb学习2：另一种打开可执行文件的方法

比起上篇博文用file的方法，这篇博文(初识gdb)的方法会更加常用一点。

程序：

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

char *MyStrCopy(const char *s1)
{
	if(NULL == s1)
	{
		return "string is NULL";
	}
	else
	{
/*
		char *s2 = (char *)malloc(strlen(s1)+1);
		if(NULL == s2)
		{
			return "malloc error";
		}*/
		char *s2 = NULL;
		char *p = s2;
		while((*s2++ = *s1++));
		return p;
	}	
}

int main(int argv,char **argc)
{
	const char *str1 = NULL;
	const char *str2 = "string copying";
	printf("%s\n",MyStrCopy(str1));
	printf("%s\n",MyStrCopy(str2));
	return 0;
}

编译运行调试：

debian:~/mc$ gcc strcopy.c -o strcopy -g -Wall 
gyz@debian:~/mc$ gdb strcopy 
Reading symbols from strcopy...done.
(gdb) l
14			char *s2 = (char *)malloc(strlen(s1)+1);
15			if(NULL == s2)
16			{
17				return "malloc error";
18			}*/
19			char *s2 = NULL;
20			char *p = s2;
21			while((*s2++ = *s1++));
22			return p;
23		}	
(gdb) l
24	}
25	
26	int main(int argv,char **argc)
27	{
28		const char *str1 = NULL;
29		const char *str2 = "string copying";
30		printf("%s\n",MyStrCopy(str1));
31		printf("%s\n",MyStrCopy(str2));
32		return 0;
33	}
(gdb) l
34	
(gdb) b 31
Breakpoint 1 at 0x739: file strcopy.c, line 31.
(gdb) info break
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x0000000000000739 in main at strcopy.c:31
(gdb) r 
Starting program: /home/gyz/mc/strcopy 
string is NULL

Breakpoint 1, main (argv=1, argc=0x7fffffffe228) at strcopy.c:31
31		printf("%s\n",MyStrCopy(str2));
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0x00005555555546f4 in MyStrCopy (s1=0x5555555547f4 "tring copying")
    at strcopy.c:21
21			while((*s2++ = *s1++));
(gdb) c
Continuing.

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
(gdb) q

解释：

1，l就是list，就是将程序显示出来；

2，直接回车，是执行上一个命令；

3，b是break，断点，设置了31行为断点；

4，info break是显示设置断点的信息；

5，r解释过了，就是run运行；

6，n是next的意思，单步运行；

7，c是continue，继续执行，直接运行结束，或者到下一个断点处。

gdb学习2：另一种打开可执行文件的方法

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