Putting functions in a header file

This is a discussion on Putting functions in a header file within the C Programming forums, part of the General Programming Boards category; Ok I am learning how to put functions that i write into a header file and then including that file ...

  1. #1
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    Question Putting functions in a header file

    Ok I am learning how to put functions that i write into a header file and then including that file in my source code. But I keep getting and error for undefined reference to rndNumber(), but the other function I have works fine when I call it. Here is the code to my header file:
    Code:
    #include <time.h>
    
    int rndNumber(int range)
    {
      int x,range; 
      srand((unsigned)time(NULL));
      x = rand()%range;
      return x;
    }
    
    void quit(void)
    {
        char x;
        printf("Press q to quit.....");
        lbl1:
        while(kbhit() == 0);
        if(getch() != 'q')
               goto lbl1;
    }
    And here is the code to my .c file:
    Code:
    #include <stdio.h>
    #include <myfunctions.h>
    
    void quit(void);
    int rndNumber(int range);
    
    int main(int argc, char *argv[])
    {
      int x;
    
      printf("Enter the range:\n");
      scanf("%i",&x);
      rndNumber(x);
      printf("The random number is %i\n",x);
      quit(); 	
      return 0;
    }
    Last edited by Vertex34; 09-29-2004 at 09:57 AM.

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    >Ok I am learning how to put functions that i write into a header file

    Don't put definitions in a header -- only declarations. I'd recommend something like this.

    myfunctions.h:
    Code:
    #ifndef MYFUNCTIONS_H
    #define MYFUNCTIONS_H
    
    int rndNumber(int range);
    void quit(void);
    
    #endif
    myfunctions.c:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
    #include <conio.h>
    #include "myfunctions.h"
    
    int rndNumber(int range)
    {
      int x; 
      srand((unsigned)time(NULL));
      x = rand()%range;
      return x;
    }
    
    void quit(void)
    {
        printf("Press q to quit.....");
        lbl1:
        while(kbhit() == 0);
        if(getch() != 'q')
               goto lbl1;
    }
    main.c:
    Code:
    #include <stdio.h>
    #include "myfunctions.h"
    
    int main(int argc, char *argv[])
    {
      int x = rndNumber(6);
      printf("The random number is %i\n",x);
      quit(); 	
      return 0;
    }
    Last edited by Dave_Sinkula; 09-29-2004 at 10:05 AM. Reason: Bothered to test it.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
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    Quote Originally Posted by Vertex34
    Code:
    lbl1:
    while(kbhit() == 0);
    if(getch() != 'q')
        goto lbl1;
    Just a side note. C version would be like:
    Code:
    do
    {
      while (kbhit() == 0);
    } while (getch() != 'q');

  4. #4
    Gawking at stupidity
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    Code:
        lbl1:
        while(kbhit() == 0);
        if(getch() != 'q')
               goto lbl1;
    This is such an insane waste of CPU cycles...
    If you understand what you're doing, you're not learning anything.

  5. #5
    Registered User
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    Ok, thanks for the advice on the CPU cycles, I will think about that a little more when I am coding.

  6. #6
    #include<xErath.h> xErath's Avatar
    Join Date
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    722
    Code:
    void quit(void)
    {
        printf("Press q to quit.....");
        lbl1:
        while(kbhit() == 0);
        if(getch() != 'q')
               goto lbl1;
    }
    //better this way...
    void quit(void)
    {
        while(getch() != 'q');
        // use exit() if you want...
        exit(0);
    }
    About the undefined references:
    if you're using an IDE and add your myfunctions.c and main.c to the default project, it should compile well.
    If you're using a command line compiler, 1st you have to compile each of the *c. files separately and then link them all together.
    Using gcc here's an examle:
    1# gcc myfunctions.c -c
    2# gcc main.c -c
    3# gcc myfunctions.o main.o -o myprog.exe
    or
    4#gcc myfunctions.c main.c -o myprog.exe
    On 1# and 2# you source files are compiled, and on 3# they're linked together to create a final executable.
    That undefined reference happens because in your main.c you include myfunctions.h which declare a function that you use. That's only a declaration, something to mention the compiler that those symbols are funtions that receive x arguments and return something. Then when you link the final file the compiler MUST know here the compiled function is, the binaries.
    4# is just a short hand for 1#,2# and 3#.
    If you're working with a large project, separating your source through several files is a way to organize you code, and to reduce compilation time, because you only need to compile the file that you change, and re-link.
    Last edited by xErath; 09-29-2004 at 07:47 PM.

  7. #7
    Banned master5001's Avatar
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    Its good that everyone was so helpful. goto statements are to C programmers as garlic is to vampires. Also, kbhit() is not a portable function. Those are only me and other being picky about what you are doing, your way works and you don't have to change it if you don't want to.

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