CODEWITHSUNDEEP
c++inheritance
jombo
jombo

Reputation: 67

Inheritance: class string

I am getting stuck with a homework which requires a self-build class called string_extend that inherits from class string. The string_extend class below is my code, and the main() part is the requested part for homework.

class string_extend:public string{
    public:
        string_extend(const string& str):string(str){}

};
int main(){
    string_extend a("amd");
    string_extend b(a);
    cout<<a<<b;
}

Could anyone give any hint about how to inherit all the functions from class string?

Upvotes: 1

Views: 257

Answers (4)

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

You can access member functions of class std::string without redeclaration them in the derived class.

A simplified version of the class can look the following way

#include <iostream>
#include <string>

int main()
{
    class string_extend : public std::string
    {
    public:
        using std::string::string;
        using std::string::operator =;

        string_extend() : std::string() {}
        string_extend( const string_extend &src ) : std::string( src ) {}
        string_extend & operator =( const string_extend &src )
        {
            std::string::operator =( src );

            return *this;
        }
    };

    string_extend s1;
    string_extend s2( { 'A', 'B', 'C' } );
    string_extend s3( "Hello" );
    string_extend s4( 8, '*' );

    std::cout << s1.size() << std::endl;
    std::cout << s2.size() << std::endl;
    std::cout << s3.size() << std::endl;
    std::cout << s4.size() << std::endl;

    std::cout << "\"" << s1 << "\"" << std::endl;
    std::cout << "\"" << s2 << "\"" << std::endl;
    std::cout << "\"" << s3 << "\"" << std::endl;
    std::cout << "\"" << s4 << "\"" << std::endl;

    s4 += { 'A', 'B', 'C' };

    std::cout << "\"" << s4 << "\"" << std::endl;
}

The program output is

0
3
5
8
""
"ABC"
"Hello"
"********"
"********ABC"

If you want you can add also the move constructor and the move assignment operator.

Upvotes: 0

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726569

Could anyone give any hint about how to inherit all the functions from class string?

Your code does that already. However, your main is not using any of string's member functions; it uses constructors, which are not inherited, unless you tell the compiler otherwise (see below).

In order to use a constructor from the base class you need to define a constructor with the same signature in your derived class. You did that for a constructor taking a string&, but not for other constructors that your main is using.

In C++03 it is done the way you did with the first constructor, i.e.

string_extend(const char* str):string(str){}

demo 1.

In C++11 you can inherit constructors:

class string_extend:public string{
    public:
        using string::string;
};

demo 2.

Upvotes: 2

Stivius
Stivius

Reputation: 72

Your class have already inherited methods from class string. You can use methods like append or insert.

Public inheritance implies that all public methods from string have become public in your class, protected and private are also the same in your class.

So you can use your objects like this:

string_extend obj("Hello world");
string_extend obj2("Test");
obj.append(obj2);

Upvotes: 0

aslg
aslg

Reputation: 1974

By declaring string as the base class publicly, your class already inherits methods from string.

Upvotes: 0

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