trouble with .h and .cpp files

**vincible** · 01-20-2010

I'm new to C++ and am having trouble implementing this extremely simple class in Visual C++:

The file testClass.h contains:

Code:

#ifndef TESTCLASS_H
#define TESTCLASS_H

class testClass
{
public:
	testClass(void);
	~testClass(void);
	vector<int> v;
};

testClass::testClass(void)
{
}

testClass::~testClass(void)
{
}
#endif

(Vector is #included in main.) That's all very simple and it compiles properly. However if I take the constructor and destructor and move them to a .cpp file, as everyone says you're supposed to do, it breaks:

file testClass.h

Code:

#ifndef TESTCLASS_H
#define TESTCLASS_H

class testClass
{
public:
	testClass(void);
	~testClass(void);
	vector<int> v;
};
#endif

with file testClass.cpp:

Code:

#include "testClass.h"

testClass::testClass(void)
{
}

testClass::~testClass(void)
{
}

After splitting the code into two files, the compiler complain about the vector<int> v; line.

syntax error : missing ';' before '<'
missing type specifier - int assumed
unexpected tokens preceding ';'

I can't figure out what I'm doing wrong here. How do I move the class's functions into a different file?

For reference, the main program was:

Code:

#include <iostream>
using namespace std;

#include <vector>
#include "testClass.h"


int main()
{
	testClass t;
	return 0;
}

Thanks in advance for any help. I've been pounding away at this for hours

**cpjust** · 01-20-2010

If you use a vector in your header file, you need to #include <vector> in your header file, not in your main.cpp.

**R.Stiltskin** · 01-20-2010

#include <vector> in testClass.h instead. The #include serves no purpose in main's file since you do not instantiate a vector in your main function.

**vincible** · 01-20-2010

Adding vector in the header file didn't change anything. (And if adding that line had helped, I would wonder why the lack of #include <vector> in the one-file version didn't lead to problems.)

Edit: aha! adding

Code:

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

made it work. Thank you!

Which leaves the question: why did I not need to add all this when all the class-related code was in the same file?

**laserlight** · 01-20-2010

Originally Posted by vincible

Which leaves the question: why did I not need to add all this when all the class-related code was in the same file?

It is a compounded mistake. You should have fully qualified the name vector<int> in the header file, i.e., std::vector<int>. In fact, using directives should not be used at namespace scope in header files, and if they are used in source files, they should be used after headers are included.

**vincible** · 01-20-2010

Originally Posted by laserlight

using directives should not be used at namespace scope in header files

I did not know this, but after googling it makes sense. Thank you.

I still do not understand why the original code compiled and ran properly, though.

**laserlight** · 01-20-2010

Originally Posted by vincible

I still do not understand why the original code compiled and ran properly, though.

You probably did something like this in the original code:

Code:

#include <vector>

using namespace std;

#include "testClass.h"

// ...

So, the <vector> inclusion and using directive were both visible to the contents of the header file, after the contents had been included in the source file.

The moral of the story: make sure that each header file includes the necessary headers that it depends on, or supplies forward declarations otherwise, and do not use using directives and using declarations at namespace scope in header files, or before a header file inclusion (if that using directive/declaration would then affect the contents of the included header).

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