C++中return作用于s.c_str()时返回结果出现乱码,该怎么处理

#include <iostream>
#include <string>
using namespace std;
string strcatEx(const char *c1, const char *c2)
{
    string s1="",s2="";
    if(c1)
        s1=c1;
    if(c2)
        s2=c2;
    return (s1+s2);
}
const char *pstrcatEx(const char *c1, const char *c2)
{
    string s=strcatEx(c1, c2);
    return s.c_str();
}
const char *pstrcatEx2(const char *c1, const char *c2)
{
    string s1="",s2="";
    if(c1)
        s1=c1;
    if(c2)
        s2=c2;
    string s=s1+s2;
    return s.c_str();
}
int main(int argc, char* argv[])
{
    
    char *c11="a12",*c12="a21a";
    cout<<strcatEx(c11, c12)<<endl;
    cout<<strcatEx(c11, c12).c_str()<<endl;
    cout<<pstrcatEx(c11, c12)<<endl;
    cout<<pstrcatEx2(c11, c12)<<endl;
    return 0;
}

//运行结果:
//VC++6.0 Debug
cout<<strcatEx(c11, c12)<<endl;          // a12a21a
cout<<strcatEx(c11, c12).c_str()<<endl;  // a12a21a
cout<<pstrcatEx(c11, c12)<<endl;         //葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺
cout<<pstrcatEx2(c11, c12)<<endl;        //葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺葺

//VC++ 6.0 Release
cout<<strcatEx(c11, c12)<<endl;          // a12a21a
cout<<strcatEx(c11, c12).c_str()<<endl;  // a12a21a
cout<<pstrcatEx(c11, c12)<<endl;         // a12a21a
cout<<pstrcatEx2(c11, c12)<<endl;        //(一个笑脸标志)8

//C-Free(MinGW5) Debug/Release
cout<<strcatEx(c11, c12)<<endl;          // a12a21a
cout<<strcatEx(c11, c12).c_str()<<endl;  // a12a21a
cout<<pstrcatEx(c11, c12)<<endl;         // a12a21a
cout<<pstrcatEx2(c11, c12)<<endl;        // a12a21a


//strcatEx(c11, c12).c_str();正常,说明不是c_str()的问题

//VC++6.0下通过调试和设置输出发现：
string s=strcatEx(c1, c2); //正常
string s=s1+s2;  //正常
s.c_str();  //正常
//出现问题的地方应该是 return 作用于 s.c_str() 时,
//返回的const char *pstrcatEx和const char *pstrcatEx2不正常