Thread: Strings in Header files

The following works fine:

Header file:

Code:

#ifndef stringproj_h
#define stringproj_h

void show(int s);
#endif

Implementation file:

Code:

#include<iostream>
#include "stringproj.h"

using namespace std;
 
void show (int s){
    cout<<s<<endl;
}

Client file

Code:

#include <iostream>
#include"stringproj.h"

using namespace std;

int main(){
    show(7);
}

But when I try to extend the same framework to strings ...:
Header file:

Code:

#ifndef stringproj_h
#define stringproj_h

#include<iostream>
#include<string>
void show(string s);
#endif

Implementation file

Code:

#include<iostream>
#include<string>
#include "stringproj.h"

using namespace std;
 
void show (string s){
    cout<<s<<endl;
}

Client file

Code:

#include <iostream>
#include"stringproj.h"
#include<string>


using namespace std;


int main(){
    show("Hello World");
}

... get 2 error messages relating to implementation file:
1. variable or field 'show' declared void;
2. 'string' was not declared in this scope;

and 1 error message relating to client file:
1.'show' was not declared in this scope

Suggestions on how to make strings work and any other observations would be much appreciated. Thanks

void show(std::string s);
string is declared in the std namespace. You get around that with using namespace std, but only in your implementation file. You don't do it in your header, so the compiler can't find it. Still, it is bad practice to use using namespace in headers, so explicitly add the std:: prefix to all standard library types in headers.