Strange Character in Programs Output:

This is a discussion on Strange Character in Programs Output: within the C Programming forums, part of the General Programming Boards category; Okay, I was trying to make a simple program to list all the files with a certain termination in a ...

  1. #1
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    Strange Character in Programs Output:

    Okay, I was trying to make a simple program to list all the files with a certain termination in a folder of my system (Slackware Linux 9) following the intructions of the book "Linux Application Development by Michael K. Johnson and Erik W. Troan" I got the following piece of code:

    Code:
    #include<stdlib.h>
    #include<sys/wait.h>
    
    int main(){
    	int result;
    	
    	result = system("exec ls *.c");
    	
    	if (!WIFEXITED(result)){
    		printf("Abnormal termination\n");}
    		else 	
    			printf("%d",result);
    	
    	exit(0);
    }
    Okay result is storing perfectly all the names of *.c files but I'm also recieving a zero in the final output here is a sample of the output:
    imanewbie@blah:~/Projects/Junk Code$ ./listsc
    array.c dinamicstack.c hashtable.c queue.c struct2.c test.c
    child.c doublepointer.c linkedlist.c random.c struct.c tripointer.c
    conta.c hamash.c listsc.c senha.c swapbytes.c
    0


    I would like to know if someone can explain me what is this 0 cause the book doesn't mention is and I don't even know what to search for in the internet. Thanks a lot.

  2. #2
    and the hat of wrongness Salem's Avatar
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    You mean the 0 printed by this

    printf("%d",result);

    Or some other zero?
    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.
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    Quote Originally Posted by Salem
    You mean the 0 printed by this

    printf("%d",result);

    Or some other zero?
    Yes the 0 from the printf("%d",result)

  4. #4
    and the hat of wrongness Salem's Avatar
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    Oh, you mean why is result 0

    Well that's the return result of the system() call.
    Which MAY in turn be the exit status of the program you tried to run.
    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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    Quote Originally Posted by Salem
    Oh, you mean why is result 0

    Well that's the return result of the system() call.
    Which MAY in turn be the exit status of the program you tried to run.
    Hum... I think you are right, system() returns 0 if succesfull, well there would be a way to me remove this 0, well not remove but hide it?

  6. #6
    Obsessed with C chrismiceli's Avatar
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    What would you like it to print?
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    Quote Originally Posted by chrismiceli
    What would you like it to print?
    I would like to print all the .c files but without the 0, I'm using it to list mp3's in fact just using .c to make a more simple example.

  8. #8
    Obsessed with C chrismiceli's Avatar
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    If you are using ls via system() to print the files, then why at all have the printf() statement. You can error check the return value of system if you want, but you don't have to print it. Just get rid of the printf() statement and it won't print the zero. Read this article about using system() and some alternatives: http://faq.cprogramming.com/cgi-bin/...&id=1043284392
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    Quote Originally Posted by chrismiceli
    If you are using ls via system() to print the files, then why at all have the printf() statement. You can error check the return value of system if you want, but you don't have to print it. Just get rid of the printf() statement and it won't print the zero. Read this article about using system() and some alternatives: http://faq.cprogramming.com/cgi-bin/...&id=1043284392
    Well I don't know if it is the problem but... I ran the program with all options of gcc for warnings and...
    gcc -c -Wall -Werror listsc.c
    listsc.c: In function `main':
    listsc.c:11: warning: implicit declaration of function `printf'


    Well my C isn't great thing so I dont know what exactly the compiler wants me to do... Any sugestions?

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    Registered User linuxdude's Avatar
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    you forgot to include <stdio.h> Don't you love that. I love the -Wall -pedantic options because they tell you that, I always forget stdlib.h with malloc and it reminds me everytime

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    Quote Originally Posted by linuxdude
    you forgot to include <stdio.h> Don't you love that. I love the -Wall -pedantic options because they tell you that, I always forget stdlib.h with malloc and it reminds me everytime
    Okay, I included stdlib.h now BUT I still recieving this misterious 0

  12. #12
    Registered User linuxdude's Avatar
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    It is printing the zero because your program ran by system() terminated normally. If you don't want it to print 0 when your system() program suceeds, then get rid of the else statement for the Abnormal termination.

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    Quote Originally Posted by linuxdude
    It is printing the zero because your program ran by system() terminated normally. If you don't want it to print 0 when your system() program suceeds, then get rid of the else statement for the Abnormal termination.
    I did it and still having the damm 0.

  14. #14
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    maragato,

    as linuxdude said, that 0 appear coz your program specifically is asking to it be printed. so, remove the else part of the if.

    jmgk

    ps: pelo teu nick, tu deve ser gaucho... entao falo em portugues: esse zero ai ta aparecendo porque tu ta imprimindo ele com o else printf()... remove essa parte ai do programa e ele vai funcionar beleza.

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    Lightbulb

    Quote Originally Posted by jmgk
    maragato,

    as linuxdude said, that 0 appear coz your program specifically is asking to it be printed. so, remove the else part of the if.

    jmgk
    ps: pelo teu nick, tu deve ser gaucho... entao falo em portugues: esse zero ai ta aparecendo porque tu ta imprimindo ele com o else printf()... remove essa parte ai do programa e ele vai funcionar beleza.

    Finally I got it! Thx a lot is is working now! Sim eu sou gaścho! Heheeheh. Dudes thanks a lot by the patience. Now I got it, the result = system("exec ls *.c");
    already prints the stuff right so I was with a damm redundant junk piece of code.

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