Question

My program collapse when I run it. If I comment out line if((str1->compare(*str2))==0 ){...} it works OK. I don’t know how to compare two elements of string * which I create and delete after comparing.

main.cpp: In function `int operator==(const Integer&, const Integer&)':
main.cpp:18: warning: taking address of temporary
main.cpp:19: warning: taking address of temporary

Integer.h

class Integer {
public:
    Integer(int val, char *opis):m_val(val),m_opis(opis)
        {
            this->m_val = 0;
            this->m_opis = strdup("0");
        }

    friend int operator==(const Integer&,const Integer&);

      private:
        int m_val;
        char *m_opis;
}

main.cpp

    int operator==(const Integer&a, const Integer&b){
        string *str1 = &string ( a.m_opis );
        string *str2 = &string ( b.m_opis );

        if((str1->compare(*str2))==0 ){return 1 ;} //<- Here is my problem i think.

        delete str1;
        delete str2;

        return 0;
    }
}
//Objects and comparing

    Integer o1(15,"lala");
    Integer o2(150,"lala");
    Integer o3;

    cout<<o1==o2;

Answer 1

The problem is that str1 and str2 are dangling pointers, as the temporary objects to which they point no longer exist by the time str1->compare() is invoked: this is what the compiler is warning about.

Don’t use dynamically objects here, use stack allocated objects:

string str1(a.m_opis);
string str2(b.m_opis);

Other points:

• prefer to use std::string instead of char* (Integer.m_opis). Related What is The Rule of Three?
• m_opis is being set twice in the constructor and all instances of Integer will have the same string "0" (same not meaning same buffer but same content). Ditto for m_val.