Pointers, Classes, and Errors o my!

This is a discussion on Pointers, Classes, and Errors o my! within the C++ Programming forums, part of the General Programming Boards category; Ok heres my class under header files as P1.h: typedef unsigned long int ULONG; class P1; { public: ULONG* pointer; ...

  1. #1
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    Pointers, Classes, and Errors o my!

    Ok heres my class under header files as P1.h:


    typedef unsigned long int ULONG;

    class P1;
    {
    public:
    ULONG* pointer;
    pointer=&h;
    private:
    ULONG h, m, s;
    return 0;
    }

    Now heres main.cpp:

    #include <iostream.h>
    #include "p1.h"

    int main()
    {
    P1 test;
    test.pointer = 100;
    cout << "test.pointer = " << test.pointer;
    return 0;
    }

    Now heres the annoying errors I get:

    --------------------Configuration: PointerNClass - Win32 Debug--------------------
    Compiling...
    main.cpp
    c:\program files\microsoft visual studio\myprojects\pointernclass\p1.h(5) : error C2447: missing function header (old-style formal list?)
    c:\program files\microsoft visual studio\myprojects\pointernclass\main.cpp(6) : error C2079: 'test' uses undefined class 'P1'
    c:\program files\microsoft visual studio\myprojects\pointernclass\main.cpp(7) : error C2228: left of '.pointer' must have class/struct/union type
    c:\program files\microsoft visual studio\myprojects\pointernclass\main.cpp(8) : error C2228: left of '.pointer' must have class/struct/union type
    Error executing cl.exe.

    PointerNClass.exe - 4 error(s), 0 warning(s)


    I am trying to learn pointers and classes. They are hard to understand and I cant figure this one out.
    Last edited by Scottc1988; 03-13-2003 at 08:53 PM.

  2. #2
    Skunkmeister Stoned_Coder's Avatar
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    missing semicolon at end of class declaration.
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  3. #3
    Skunkmeister Stoned_Coder's Avatar
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    PS.

    Didnt your mother tell you not to play with your privates in public?!
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  4. #4
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    Lol

  5. #5
    Skunkmeister Stoned_Coder's Avatar
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    btw void main is also undefined behaviour.... use int main instead and return something back to the os at the end of main commonly 0 is returned.
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  6. #6
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    Guess you shouldn´t be making statements in class declaration:

    Code:
    pointer=&h;
    Do this in your constructor instead!

  7. #7
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    I dont understand constructor/destructors.

  8. #8
    Skunkmeister Stoned_Coder's Avatar
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    nope dont need those () after P1 either
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  9. #9
    Skunkmeister Stoned_Coder's Avatar
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    its simple a constructor is called to make an object and a destructor is called to destroy an object.

    your class...
    Code:
    class P1
    {
    public:
        typedef unsigned long ULONG;
        P1() : h(0),m(0),s(0) {} // constructor. syntax looks daunting
        P1( ULONG H,ULONG M,ULONG S) 
            { 
                 h = H;
                 m=( M > 59 )? 59 : M ;
                 s = (S > 59 ) ? 59:S;
             }
         P1( const P1& rhs ) : h(rhs.h),m(rhs.m),s(rhs.s) {}
         ~P1() {} // the do nothing destructor
    private:
        ULONG h, m, s;
    };
    Notice we have three constructors.
    the first allows us to do this....
    Code:
    P1 myp1;
    Its called a default constructor.
    The next allows us to do this...
    Code:
    P1 myp1 (10,10,10);
    constructing from ULONG,ULONG,ULONG
    the last one is called the copy constructor. This constructs from another P1 object.
    Code:
    P1 a;
    P1 b(a);
    The destructor does othing in this example as there are no resources to be freed. Destructors get heavier use when you deal with dynamic memory.
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  10. #10
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    return 0; ?

    class p1
    { ...
    return 0; // ???
    };

  11. #11
    Skunkmeister Stoned_Coder's Avatar
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    int main()
    {
    // do stuff here
    return 0;
    }
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  12. #12
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    This should work...although its not using the header file like you want.

    Code:
    #include <iostream.h>
    
    typedef unsigned long ULONG;
    
    class P1{
    public:
    ULONG* pointer;
    P1() { pointer = &h; }  // constructor
    display();
    private:
    ULONG h, m, s;
    };
    
    int main()  //always use int main ( )
    {
    P1 *test;	   // Make it a pointer so you can allocate dynamic memory
    test = new P1; // You must allocate memory 
    
    // the value of the pointer should be = 100
    
    *test->pointer = 10;  
    
    cout << "test.pointer = ";
    
    test->display();
    
    return 0;  // always return a value
    }
    
    P1::display()
    {
    	cout << *pointer << endl;
    }

  13. #13
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    you should delete at the end too

    delete test;

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