Operator overload question

[econy]

Please read the following code:

class MyString {
private:
char *str;
public :
MyString():str(NULL){}
MyString(const char* iStr);
MyString(const MyString& iMyStr);
~MyString();

MyString& operator=(const MyString &iMystr);

//friend MyString& operator+(const char\* iStr, const MyString& iMyStr);
friend char\* operator+(const char\* iStr, const MyString& iMyStr);

};

//Friend + , "xxx" + S
char* operator+(const char* iStr, const MyString& iMyStr)
{
char * newStr = NULL;
newStr = new char[strlen(iStr)+strlen(iMyStr.c_str()) + 1];
strcpy(newStr,iStr);
strcat(newStr,iMyStr.c_str());

return newStr; //works well
    //return MyString(newStr); // compile error

}

int main()
{
MyString S1("fgh");
MyString S2("abc");

S1 = "cde" + S1;
return 0;
}

I set break point, and I found if I use commented statements, compiler popups exception. But I think both commented statements ,and non comment statements are same.both use constructor to construct a temporary object. Don't know why it does not work.

[Richard Andrew x64]

Well of course it gives a compile error, you have declared the return value of operator+ to be char* instead of MyString&.

char* operator+(const char* iStr, const MyString& iMyStr)
{
char * newStr = NULL;
newStr = new char[strlen(iStr)+strlen(iMyStr.c_str()) + 1];
strcpy(newStr,iStr);
strcat(newStr,iMyStr.c_str());

return newStr; //works well
    //return MyString(newStr); // compile error ----- DOESN'T MATCH RETURN TYPE

}

The difficult we do right away... ...the impossible takes slightly longer.

[CPallini]

Please don't do that. Such a operator should only return a MyString reference.

Veni, vidi, vici.

[econy]

In class declaration, it has a constructor:

MyString(const char * istr);

[econy]

but, I use :

return MyString(newStr);

I got a compile error message.

[Lost User]

The implementation of your overload must match the definition, in parameters and return type. You are trying to define the overload as:

friend MyString& operator+(const char* iStr, const MyString& iMyStr);

and the implementation as:

char* operator+(const char* iStr, const MyString& iMyStr)
{
}

The return types are different.

[CPallini]

You have to change the method signature. It is safe to add a C-like string to a MyString object and then return a reference to the latter:

MyString & operator+(MyString & iMyStr, const char * str);

Veni, vidi, vici.