Template class generate errors in C++

Question

This program is not compiling. What's the problem?

#include<iostream>
#include<map>
using namespace std;

template<class T>class Data{
    string header;
    T data;
public:
    Data(string h, T d){header = h, data = d;}
    void WriteData()
    {
        cout<<header<<": "<<data<<endl;
    }
};


int main(int argc, _TCHAR* argv[])
{
    Data<int> idata("Roll", 100);

    Data<string>sdata("Name","Jakir");

    idata.WriteData();
    sdata.WriteData();
    return 0;
}

Showing the following errors.

error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'std::string' (or there is no acceptable conversion) c:\program files (x86)\microsoft visual studio 10.0\vc\include\ostream(679): could be 'std::basic_ostream<_Elem,_Traits> &std::operator <<>(std::basic_ostream<_Elem,_Traits> &,const char *)' with [ _Elem=char, _Traits=std::char_traits ]

while trying to match the argument list '(std::ostream, std::string)' .....\maptest\mapt\mapt\mapt.cpp(16) : while compiling class template member function 'void Data::WriteData(void)' with [ T=int ]

Andy Prowl · Accepted Answer · 2013-04-21 10:06:42Z

9

It seems you forgot to:

 #include <string>

You cannot count on transitive inclusion of all the necessary header files because some other header like <iostream> may #include them.

If you are using std::strings, you should be #includeing the appropriate header (<string>) explicitly.

Overloads of operator << which accept an std::string are probably declared/defined in a header which is not #included by <iostream>.

Besides, avoid having using directives at global namespace scope such as this:

using namespace std;

They can easily lead to name clashes and it is normally regarded as a bad programming practice.

edited Apr 21, 2013 at 10:06

answered Apr 21, 2013 at 9:26

Andy Prowl

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2 Comments

Jakir Hossain Over a year ago

Oh my god. What a mistake I've made. Thanks a lot. It spoiled my 2 hours. thanks again.

Andy Prowl Over a year ago

@JakirHossain: We've all been there ;) Good luck with your project

Mohit Shah · Accepted Answer · 2013-04-21 09:42:02Z

2

T_char is incorrect type as argv should have a type for example char*

Correct source code is

#include<iostream>
#include<map>
#include<string>
using namespace std;

template<class T>class Data{
    string header;
    T data;
public:
    Data(string h, T d){header = h, data = d;}
    void WriteData()
    {
        cout<<header<<": "<<data<<endl;
    }
};


int main(int argc, char* argv[])
{
    Data<int> idata("Roll", 100);

    Data<string>sdata("Name","Jakir");

    idata.WriteData();
    sdata.WriteData();
    return 0;
}

answered Apr 21, 2013 at 9:42

Mohit Shah

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