Using header files problem!

This is a discussion on Using header files problem! within the C++ Programming forums, part of the General Programming Boards category; Day 6 of 21 My objective : To compile and execute a program which uses my custom "math class" for ...

  1. #1
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    Using header files problem!

    Day 6 of 21

    My objective: To compile and execute a program which uses my custom "math class" for basic math functions
    My problem: I am getting a compiler error (take a look at the exact compile error I have included at the bottom of this thread)

    Here is the code of my three files (Main.cpp, MikesMath.h, MikesMath.cpp):

    Main.cpp
    Code:
    #include <iostream>
    #include "MikesMath.h"
    
    using namespace std;
    
    int main()
    {
        cout << "Hello: " << add(2,2) << endl;
        
        system("PAUSE");
        return 0;
    }
    MikesMath.h
    Code:
    #ifndef MIKESMATH_H_
    #define MIKESMATH_H_
    
    class MikesMath
    {
    public:
           MikesMath();
           ~MikesMath();
           int add(int x, int y);
           int multiply(int x, int y);
    };
    
    #endif
    MikesMath.cpp
    Code:
    #include "MikesMath.h"
    
    int MikesMath::add(int x, int y)
    {
        return x + y;
    }
    
    int MikesMath::multiply(int x, int y)
    {
        return x * y;
    }
    
    MikesMath::MikesMath()
    {
    
    }
    MikesMath::~MikesMath()
    {
                           
    }
    Here is what my compiler (GCC compiler/Using DevC++) is spitting at me:
    Image:
    http://img543.imageshack.us/img543/8...pilererror.png
    Last edited by Always; 08-05-2011 at 07:35 AM. Reason: To correct a capitalization error and a quick grammar fix

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    Note that that is not a compiler error. The clue is the [Linker error] at the beginning. You need to put all your .cpp files in your project. If you don't have a project, then you need to make a project and put all your .cpp files in it.

  3. #3
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    Oh, alright. I also have one quick question. Is there a way to make my class like iostream where I can include it into any of my other programs without having to add it in the project?

    With just like a "#include <mikesmath.h>"

  4. #4
    Registered User rogster001's Avatar
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    well it is still included in the project but yes., you create a header file called mikesmath.h and add it to the project, in there you put your own class definitions and function declarations. i would use " " instead of < > when it is your own header file.

    Unless you mean only include the header file and not have to have the actual working code, function definitions visible?
    Last edited by rogster001; 08-05-2011 at 07:45 AM.
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  5. #5
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Always View Post
    Oh, alright. I also have one quick question. Is there a way to make my class like iostream where I can include it into any of my other programs without having to add it in the project?

    With just like a "#include <mikesmath.h>"
    iostream (as part of the C++ runtime) has to be added to your project. However, it has already been done for you.

  6. #6
    and the hat of wrongness Salem's Avatar
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    Well the initial problem is that you're writing a console program (with main), but the IDE tried to create a GUI program (expected to start at winmain), and this failed.

    > cout << "Hello: " << add(2,2) << endl;
    This is not invoking your class member function. You need a class instance variable to make this happen.

    Also, dev-c++ can be a rather buggy IDE, and has not been updated for a good few years now (nor will it be)
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  7. #7
    C++まいる!Cをこわせ! Elysia's Avatar
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    MaikesMath math;
    std::cout << math.add(2, 2);

    Also, to address other concerns...
    iostream is never "included by default" (unless you mean the actual implementation and not the declarations/definitions). You must always include <iostream> to use it. The same goes for your class. And since the implementation is not in your header, you must also add your source file to your project.
    Are there ways around that? Yes, by using static libraries or DLLs and configuring your IDE to always search the appropriate .lib file you create. But that's probably too advanced for you right now.
    In any case, you must always include the header file. No way around that.

    You should also switch IDE and create a "Console application." Not a Windows Application, Windows Forms Application, Win32 Application or anything like it. Just a console application.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  8. #8
    Algorithm Dissector iMalc's Avatar
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    You shouldn't actually be using a class in this instance as you have no member variables. What you actually want is just a namespace.
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