Thread: Never used Sprintf before. My program crashes once the sprintf should begin

  1. #1
    Registered User
    Join Date
    Feb 2010

    Never used Sprintf before. My program crashes once the sprintf should begin

    The purpose of this code is to let the user enter a name of a song into a string, which can then be buffered and played into a program called 'mplayer'.

    #include <stdio.h> 
    #include <stdlib.h> 
    #include <unistd.h>
    int main(void)
        int menu, option, playchoice;       // for switch case- ignore this.
        char song[20];                            // string for song name
                                       printf("Which song?"); 
                                       scanf("%s", &song);    // sets song name to 'song'
                                       sprintf("buffer, system(%s)", song);        
                                       sprintf("buffer.mplayer %s", song);
    I have just selected the bits relating to this code as the other code (switch statements) are not the problem.

    This is for a program called 'mplayer'. There are no compiling errors. It just stops responding and Windows closes it. I am new to programming and have had difficulties getting this far.

    Thanks for any help!

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    char buffer[100];
    sprintf( buffer, "mplayer %s", song );
    system( buffer );
    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.

  3. #3
    Join Date
    Oct 2007
    Inside my computer
    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.

  4. #4
    Registered User
    Join Date
    Feb 2010
    Thank you SO much Salem! This makes more sense than the rubbish I wrote lol.

  5. #5
    Algorithm Dissector iMalc's Avatar
    Join Date
    Dec 2005
    New Zealand
    You should also prevent buffer overflow by modifying your scanf line to have something like "%19s" rather than just "%s".
    Of course I would make the song buffer much larger first, perhaps MAX_PATH+1 in size.
    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"

  6. #6
    Registered User
    Join Date
    Feb 2010
    Thank you, iMalc!. I'll look into this. We haven't even learnt about buffering yet, but I have a rough idea, so this will be useful when I've looked into it!

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