User defined Header

hi, here I am again. I'm in the pace where you will code a header or header of your own in a different file for program reusability. I have tried the code many times in different ways. I decided to make it small as shown below so that I could easily check the error quickly, unfortunately, I cannot see any problem in my code. I have no idea what's happening, but I've searched over the net and they have the same structure as mine. I don't know if it's with the compiler, but if I created Name.h without seperating the implementation of that class it works. I hope you could help me with this and give some advice. Hope to hear from you soon.

file: Name.h

Code:

---

#include <string>
using std::string;

class Name
{
      public:
            Name( string );
            void setName( string );
            string getName();
            void displayName();
           
      private:
              string name;
};

---

file: Name.cpp

Code:

---

#include <iostream>
using std::cout;
using std::endl;

#include "Name.h"

Name::Name( string n )
{
  setName( n );
}
void Name::setName( string n )
{
  name = n;
}
string Name::getName()
{
  return name;
}
void Name::displayName()
{
    cout << "Name: " << getName() << endl;
}

---

file: Person.cpp

Code:

---

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

#include "Name.h"

int main( void )
{
    Name emp1( "John Travolta" );
    Name emp2( "Nicolas Cage" );
   
    cin.get();
    return 0;
}

---

Error:
C:\DOCUME~1\INFORM~1\LOCALS~1\Temp\ccYbcaaa.o(.tex t+0x1ac) In function `main':
[Linker error] undefined reference to `Name::Name(std::string)'
[Linker error] undefined reference to `Name::Name(std::string)'
C:\DOCUME~1\INFORM~1\LOCALS~1\Temp\ccYbcaaa.o(.tex t+0x1ac) ld returned 1 exit status

Compiler:
DevC++ 4.9.9.2

You are compiling as a project, yes? Each file compiles separately and then gets linked together by the linker -- if you didn't compile Name.cpp into Name.o, it can't get linked in.

thanks for replying. um, I'm not creating a project. I'm reading a book and reached that topic about program reusability. I compiled name.cpp, I got this result from the compiler.

Error:
[Linker error] undefined reference to `WinMain@16'
ld returned 1 exit status

You haven't defined main(). Every C program needs an entry function called main, and it must return int.

Quote:

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You haven't defined main(). Every C program needs an entry function called main, and it must return int.

---

hi, thanks for replying. I have a main function in person.cpp. I don't need a main function name.cpp because that's not the program that should have the main function.

Quote:

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Originally Posted by $l4xklynx

thanks for replying. um, I'm not creating a project.

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Two source files == project.

Quote:

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Originally Posted by tabstop

Two source files == project.

---

thanks, but I wasn't able to fix the problem yet.

You need to compile both .cpp files, and link them. No separately.
Or you can use an IDE and put them into a project, which will make the IDE compile all the files.

you failed to include Name.o (or whatever it is called) in the filelist to be used by the linker...

I Tried to compile the Name.cpp
I got this error message:

Code:

---

  [Linker error] undefined reference to `WinMain@16'
  ld returned 1 exit status

---

so I guess I cannot link both of them if there's an error message. I tried to put a main in the Name.cpp file, it was successfull but the Person.cpp doesn't it load it successfully still. I've seen lots of programs that is creating their own .h file to separate classes so I hope I could do that as well.


I've tried the code at the bottom and it worked, wierd. When I load the ( #include "Name.cpp" ) does it load the ( #include "Name.h" ) that was loaded by that .cpp file?.

Code:

---

#include <iostream>
using namespace::std;

#include "Name.cpp"

int main( void )
{
    Name emp1( "John Travolta" );
    Name emp2( "Nicolas Cage" );
   
    emp1.displayName();
    emp2.displayName();
   
    cin.get();
    return 0;
}

---

I wasn't aware of the linking process. I'm using DevC++ 4.9.9.2. I think I have to research about that. Is that something that I will hard code? or something that will do in my compiler for the compiler to link the two files?

sorry for the lack of knowledge about this, I'm just self studying. I have no private teacher or in a school learning this, so it's kinda hard. But I'm willing to learn so everyday I have nothing to do at home but to exhaust myself in programming and trying to understand all things on my own.

Firstly, do not include .cpp files. Remember that as a rule.
Secondly, there are two stages to compiling:
- Compiling.
- Linking.
First, you must compile both files.
Then you must link both files.
Do not do these separately. Do not compile & link each file separately. It won't work.

If this is too difficult for you, use an IDE such as Code::Blocks or Visual Studio. It will do this for you automatically.

If you are using command line compilation, then you need to do something like this:

Code:

---

gcc -c name.cpp
gcc -c person.cpp
gcc -o person person.o name.o

---

The -c switch tells the compiler that the source file you supplied is NOT the complete source for the application, and thus it should not try to link... The last line takes the object files produced by the compile steps and links them together, along with the C runtime library.

--
Mats

If you're getting an error about WinMain then you aren't compiling it as a Console App, you're compiling it as a Windows App. You need to change that, but I've never used DevC++ so I can't help you with that.

Also, you need some header guards in your .h file and get that using statement out of the header; you should never put a using statement in a header file.

Quote:

---

Originally Posted by cpjust

If you're getting an error about WinMain then you aren't compiling it as a Console App, you're compiling it as a Windows App. You need to change that, but I've never used DevC++ so I can't help you with that.

Also, you need some header guards in your .h file and get that using statement out of the header; you should never put a using statement in a header file.

---

No, gcc looks for EITHER main or winmain, no matter what - it doesn't have a setting for the linker to translate from one to the other, so it accepts both.

--
Mats

Oh, and
int main( void )

You don't need void in the parameter list in C++. It's unnecessary - it just takes space with no effect!

Quote:

---

Firstly, do not include .cpp files. Remember that as a rule.

---

One exception... templates. Although I call those hpp's.

Well, templates are usually put in headers, yes?
I always put them in headers.

Quote:

---

Originally Posted by Elysia

Well, templates are usually put in headers, yes?

---

I am sure that you recall the trick of placing the implementation of the templates into a .cpp file, and then including that in the .h file.

Of course, if you were feeling silly enough, you could use ".h" for source file extensions and ".cpp" for header file extensions.

I remember that trick, but I don't use it. All my templates go into headers.
So, I never include .cpp files. Ever.

I find it useful to include a separate hpp for template source. IMO, putting it all in the header makes the header ugly and cumbersome and breaks the paradigm that all your other non- template classes follow.

But I digress.....

thanks for all the replies.

Quote:

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Also, you need some header guards in your .h file and get that using statement out of the header; you should never put a using statement in a header file.

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if I'm not wrong, I read that i have to use the using statement for I will be using it in loading the file .h.

Code:

---

#include <string>
using std::string;

class Name
{
      public:
            Name( string );
            void setName( string );
            string getName();
            void displayName();
           
      private:
      string name;
};

---

the one in blue uses the class string ( I'm not sure if the string is class) if I will not use the using std::string it will cause a problem on loading the .h from the main file.

Quote:

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You don't need void in the parameter list in C++. It's unnecessary - it just takes space with no effect!

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thanks, next time I post a program you will never see void there in the parameter ^_^

Quote:

---

If this is too difficult for you, use an IDE such as Code::Blocks or Visual Studio. It will do this for you automatically.

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thanks for the advice, but I prefer to know how linking works. I kept researching about that but until now I can't find any resource on how to link those two .cpp and use the .h file ro your main program.

You don't need to have a using declaration for using std::string. You can also explicitly qualify it.

Therefore, replace all occurences of 'string' in the class definition (not only the blue one, but also those in the member functions) with 'std::string'.

Quote:

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Originally Posted by $l4xklynx

thanks for the advice, but I prefer to know how linking works. I kept researching about that but until now I can't find any resource on how to link those two .cpp and use the .h file ro your main program.

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Alright, that's your decision.
But usually, you just do like
g++ file1.cpp file2.cpp [options]
And it compiles and links all files together. One program, one file.

See this for more details: Chapter 59. Don't write namespace usings in a header file or before an #include

Quote:

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Originally Posted by cpjust

See this for more details: Chapter 59. Don't write namespace usings in a header file or before an #include

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wow, I never knew that, but I just copied the program from the book I read. I will not tell the name of the book to protect their integrity. But how come? they should know that. Anyway, I removed the #include <string> and using namespace.

Code:

---

#ifndef NAME_H
#define NAME_H

//#include <string>
//using std::string;

class Name
{
      public:
            Name();
            Name( string );
            void setName( string );
            string getName();
            void displayName();
           
      private:
              string name;
};
#endif

---

Yes, they should know that. A lot of authors should also know things such as int main() instead of void main(), but I guess these days almost anyone can publish a book full of crap. :)

Quote:

---

Originally Posted by $l4xklynx

Code:

---

#ifndef NAME_H
#define NAME_H

//#include <string>
//using std::string;

class Name
{
      public:
            Name();
            Name( string );
            void setName( string );
            string getName();
            void displayName();
           
      private:
              string name;
};
#endif

---

---

http://apps.sourceforge.net/mediawik...arameter_names

No, no, now your header has include order dependencies. It requires that someone includes <string> and imports string into the global namespace before it can be included without errors. That's just as bad, if not worse, as having using statements or declarations. The correct form is

Code:

---

#ifndef NAME_H
#define NAME_H

#include <string>

class Name
{
      public:
            Name();
            Name( std::string );
            void setName( std::string );
            std::string getName();
            void displayName();
           
      private:
              std::string name;
};
#endif

---

The advice about parameter names is good, too.

I was able to fix the problem. My mistake before was I didn't build a project, instead, I coded all of them in separate files one-by-one but not as a whole project.

Having problem with this at the bottom:

Not grouped as one project
Name.h
Name.cpp
People.pp


When I consolidated all of the files in one project the program compiled successfully.

Grouped in one project
+Name.h
+Name.cpp
+People.cpp

Somehow, I'm happy to fix it but I didn't get the idea on how to link those two manually. So with the compiler I have I don't have any option to link those two files that I wanted to link manually right? even with visual c++?

If you were typing commands, you would just type "gcc -o Name.exe Name.cpp People.cpp" (giving all the files that need to be compiled on one line). Same for Visual Studio's cl, except I forget what the equivalent of -o is.

Is there any compiler that I could use to do manual linking or all the stuffs are manual? I wanted to understand things in detail, like how the linker works and how to link two files something like that.. Is there any good tutorial or website that you could provide?

Well, you could do

Code:

---

cl /c Name.cpp
cl /c People.cpp
# At this point, you should have a Name.obj and a People.obj
link Name.obj People.obj

---

cl requires some special switches or you will end up with a broken executable or warnings. Not the friendliest compiler.
I believe you have to specify to use exceptions or not, or you will get a warning.

thanks for all the replies... I will be doing all your advices..