C++ define class in head file, and implement its member in source file

Question

when i build this project in vs2010, error occurs:

syntax error : missing ';' before identifier 'b'
error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

error C2065: 'b' : undeclared identifier

#ifndef _B_H
#define _B_H

#include <string>

class B
{
public:
    B();
    ~B();
    void showfunc();

    string b;
};

#endif

/***************************/
// B.cpp
#include <iostream>
#include <string>
#include "B.h"
using namespace std;
B::B()
{
}
void B::showfunc()
{
 cout<<b<<endl;
}
/**************************************/
// main.cpp
#include <iostream>
// #include "B.h"
using namespace std;
void main()
{ 
}

Please help me!

`string` is in the `std` namespace. You need `std::string b;` — juanchopanza, Nov 05 '13 at 08:33

score 1 · Answer 1 · edited May 23 '17 at 12:13

1

string is in the std namespace. You need

std::string b;

You should also be be careful with using namespace std, even in implementation files.

Also, note that void main() is not one of the standard signatures for main in C++. You need

int main() { ...

edited May 23 '17 at 12:13

Community

1
1

answered Nov 05 '13 at 08:35

juanchopanza

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I added **using namespace std;** at the beginning of the head file B.h, and it works. It's troublesome to add std prefix everytime when using classes in the `std` namespace. But in fact i have **using namespace std;** sentence at the head of source file **B.cpp**. why it doesn't work? – Barnett_Love Nov 05 '13 at 10:06
@Barnett_Love You should not use `using namespace std`. It is more trouble than it is worth. You will deeply regret it one day. As to your question, putting that in `B.cpp` has no effect on `B.h`. – juanchopanza Nov 05 '13 at 10:15

score 0 · Answer 2 · edited Nov 05 '13 at 08:57

0

add std to string

std::string b;

edited Nov 05 '13 at 08:57

Stephane Delcroix

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answered Nov 05 '13 at 08:37

CroCo

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thanks a lot. I added **using namespace std;** at the beginning of the head file B.h, and it works. – Barnett_Love Nov 05 '13 at 09:59

C++ define class in head file, and implement its member in source file

2 Answers2