反转字符串问题

C/C++ code

char *revstr(char *str, size_t len){    char    *start = str;    char    *end = str + len - 1;    char    ch;    if (str != NULL)    {        while (start < end)        {            ch = *start;            *start++ = *end;    //在这个位置出错            *end-- = ch;        }    }    return str;}int _tmain(int argc, _TCHAR* argv[]){        char *ch = "123456";    revstr(ch,6);    cout<< ch<<endl;    return 0;}

运行的时候总是出现这种错误：写入位置 0x004176fc 时发生访问冲突，快抓狂了~~~

[解决办法]
const常量不能修改
char *ch = "123456";
隐士转换为const char
[解决办法]

C/C++ code

 char *ch = "123456";