strcpy的实现问题。。。。

char*strcpy(char *s1, char *s2)
{
char*temp = s1;
while (*s2 != '\0')
{
*s1++ = *s2++;
}
s1 = '\0';
return temp;
}

为什么一运行到*s1++=*s2++就出错。新人求教

main函数中修改：
char *s1="abc"; s1指向静态常量存储区域，一般不允许通过指针修改

    char s1[]="abc", s2[]="def";

#include<stdio.h>
//strcpy 的实现
char* strcpy1(char *s,char *t)
{
   char *temp = s ;  
   while((*s++ = *t++))
  ;
   return temp;......
答案就在这里：strcpy实现 空指针的问题。
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 #include"stdio.h"
char*strcpy(char *s1, char *s2)
{
    char*temp = s1;
    while (*s2 != '\0')
    {
        *s1++ = *s2++;
    }
    *s1 = '\0';//修改
    return temp;
}

int main()
{
    char str1[20],str2[20]="i love vc";
    strcpy(str1,str2);
    printf("%s\n",str1);
}

 #include<iostream>
using namespace std;
int strcmp(char *s1, char *s2)
{
    while (*s1 != '\0'&&*s2 != '\0'&&*s1 == *s2)
    {
        s1++;
        s2++;
    }
    return *s1 - *s2;
}
char*strcpy(char *s1, char *s2)
{
    char*temp = s1;
    while (*s2 != '\0')
    {
        cout << *s1 << endl;
        *s1++ = *s2++;
    }
    *s1 = '\0';
    return temp;
}
char*strcat(char *s1, char *s2)
{
    char*temp = s1;
    while (*s1 != '\0') s1++;
    while (*s2 != '\0')
    {
        *s1++ = *s2++;
    }
    *s1 = '\0';
    return temp;
}
int strlen(char *s1)
{
    int i = 0;
    for (i = 0; s1[i] != '\0'; i++);
    return i;
}
void main()
{
    char*s1="abc", *s2="def";
    cout << "strlen(s1)=" << strlen(s1) << endl;
    cout << "strlen(s2)=" << strlen(s2) << endl;
    cout << "strcmp(s1,s2)=" << strcmp(s1, s2) << endl;
    cout << "strcpy(s1,s2)=" << strcpy(s1, s2) << endl;
    cout << "strcat(s1,s2)=" << strcpy(s1, s2) << endl;
}