"The Devil function"

This is a discussion on "The Devil function" within the C Programming forums, part of the General Programming Boards category; I have a sentence to be read, that sentece will give me the values of X2 and Y2, The function ...

  1. #1
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    "The Devil function"

    I have a sentence to be read, that sentece will give me the values of X2 and Y2,
    The function is called readNext(arg), but it crashes when i call it, can't find out why. (no error message on windows).

    Code:
    int x1,x2,y1,y2;
    x1 = x2 = y1 = y2 = 0;
    
    readNext(x2);
    readNext(y2);
    
    ///End of code///
    
    //This function receives them:
    
        void readNext(int *arg1) {
             *arg1 = -1;
             printf("ok");
         while(*arg1 < 0 || isdigit(c)) {
             if(isdigit(c))
              *arg1 = (*arg1 < 0) ? (int)(c-'0') : *arg1 * 10 + (int)(c-'0');
           printf("3o3 arg1 = %i\n",*arg1);
           if(c==';') break;
           c = getchar();
          }
        }
    But in Windows it just crashes, and i can't test it on linux yet.
    Can you find out where's the error?

    Thanks!

  2. #2
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    Ok i know the error now,
    its a "Segmentation fault (core dumped)" error as usual in critical moments...

  3. #3
    a_capitalist_story
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    Run it in a debugger.

  4. #4
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    Quote Originally Posted by rags_to_riches View Post
    Run it in a debugger.
    What's the best debugger to do it?

  5. #5
    Jack of many languages Dino's Avatar
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    Quote Originally Posted by Milhas View Post
    I have a sentence to be read, that sentece will give me the values of X2 and Y2,
    The function is called readNext(arg), but it crashes when i call it, can't find out why. (no error message on windows).

    Code:
    int x1,x2,y1,y2;
    x1 = x2 = y1 = y2 = 0;
    
    readNext(x2);
    readNext(y2);
    
    ///End of code///
    
    //This function receives them:
    
        void readNext(int *arg1) {
             *arg1 = -1;
             printf("ok");
         while(*arg1 < 0 || isdigit(c)) {
             if(isdigit(c))
              *arg1 = (*arg1 < 0) ? (int)(c-'0') : *arg1 * 10 + (int)(c-'0');
           printf("3o3 arg1 = %i\n",*arg1);
           if(c==';') break;
           c = getchar();
          }
        }
    But in Windows it just crashes, and i can't test it on linux yet.
    Can you find out where's the error?

    Thanks!
    You are passing an integer to readNext(), but receiving it as a pointer to an integer.

    Todd
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

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    Code:
    int x1,x2,y1,y2;
    ...
    readNext(x2);
    readNext(y2);
    ...
        void readNext(int *arg1) {
    Look at those 4 lines of code. Look at them HARD. And if you still don't see the problem, look at them HARDER!

    -- edit --
    Aw Todd. You ruined my fun!

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    Thanks,
    so i'll have to make that function to return a result right? (not being void)

  8. #8
    a_capitalist_story
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    Quote Originally Posted by Milhas View Post
    What's the best debugger to do it?
    Totally depends on the operating system and IDE. Visual Studio is great for Windows, gdb is great for Linux, Sun Workshop is great for Solaris (or was, it's been a while)...

    You'll find it hard to be a competent developer in compiled languages if you are unable to use a debugger proficiently.

  9. #9
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    Quote Originally Posted by Milhas View Post
    Thanks,
    so i'll have to make that function to return a result right? (not being void)
    I don't think you're looking at those 4 lines hard enough. Look at them HARDER:
    Code:
    int x1,x2,y1,y2;
    ...
    readNext(x2);
    readNext(y2);
    ...
        void readNext(int *arg1) {

  10. #10
    Jack of many languages Dino's Avatar
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    Quote Originally Posted by arpsmack View Post
    I don't think you're looking at those 4 lines hard enough. Look at them HARDER:
    Too funny! (Or, just read the other posts in this thread. duh.)
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  11. #11
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    Oh right! Look at those 4 lines HARDER... and listen to Todd. Or I suppose you could just pick one of those two.

  12. #12
    Algorithm Dissector iMalc's Avatar
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    What wrong with simply using scanf? It looks like you're reimplementing the wheel!
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

  13. #13
    C++まいる!Cをこわせ! Elysia's Avatar
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    You need to start paying attention to compiler warnings and errors. Turn the warnings up to max, as well.
    You should never let implicit cast to a pointer from a non-pointer type compile.
    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.

  14. #14
    and the hat of wrongness Salem's Avatar
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    As Elysia says, turn up the warning level, and don't run the code until it clean compiles.

    It's no guarantee of success, but you certainly improve the odds in the long run.

    Think about the difference between
    readNext(x2);
    readNext(&x2);
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    Yes, that solves it, &x2 instead of x2.

    This tiny details still make me confusion sometimes..

    Thanks

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