Question

I’ve created a class myString and I’m trying to run the following code:

class myString{
    char* str;
    int len;

public:
    myString(char* str1 = " "){
        len = strlen(str1);
        str = new char[len+1];
        strcpy(str, str1);
    };

    int getLen() const {
        return len;
    };

    char* getString() const {
        return str;
    };

    ~myString(){
        delete[] str;
    };

    myString& operator=(myString& orig){
        cout << "hello";
        if (str == NULL){
            delete[] str;
        };
        str = new char[orig.getLen()];
        strcpy(str, orig.getString());
        cout << this << endl;
        return *this;
    };

    ...
};



int main(){


    myString s("bla");
    myString k("dingo");
        myString g = s;
        // s=k;  //When this line is commented I get a linking error
         ...
   };

My Questions:

1. Why “hello” does not get printed?
2. Why the line s=k causes a linker error?

This is the error:

LINK : c:\users\perry\documents\visual studio
2010\Projects\inheritance\Debug\inheritance.exe not found or not built
by the last incremental link; performing full link 1>main.obj : error
LNK2019: unresolved external symbol “class
std::basic_ostream > & __cdecl
operator<<(class std::basic_ostream

&,class myString *)” (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@PAVmyString@@@Z)
referenced in function “public: class myString & __thiscall
myString::operator=(class myString &)” (??4myString@@QAEAAV0@AAV0@@Z)
1>c:\users\perry\documents\visual studio
2010\Projects\inheritance\Debug\inheritance.exe : fatal error LNK1120:
1 unresolved externals

Thanks,
Li

Answer 1

For the following, you need a copy constructor. It does not use the assignment operator function.

myString g = s;

Edit

For the linker error – I can’t help you with that. Rather than guessing at what operator<< that line calls, I will just give up on this because you haven’t provided the code. In normal C++ code, there is no way that a simple cout << this; would cause a linker error. cout has an operator that accepts a void const* for this. You have declared an operator somewhere that provides a better match but did not define it.