Garbage appearing

This is a discussion on Garbage appearing within the C Programming forums, part of the General Programming Boards category; Hey guys, I'm once again sending a phrase (in this case, it's only a simple command) through my pipe and ...

  1. #1
    C Beginner
    Join Date
    Dec 2011
    Location
    Portugal
    Posts
    187

    Garbage appearing

    Hey guys,
    I'm once again sending a phrase (in this case, it's only a simple command) through my pipe and when server receives it instead of printing it it prints this a square with 0's and 1's inside (wtf?).

    My client code is the following :
    Code:
    #include <sys/types.h>#include <sys/stat.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <string.h>
    
    
    #define MAX_COMANDO 10
    
    
    char* juntarg(char *arg[])
    {
         char *frase=strdup(arg[1]);
         strcat(frase," ");
        return frase;
    }
    
    
    void ajuda()
    {
        printf("\n|------------------------- Ajuda ----------------------------------------|\n");
        printf(" Para adicionar um ficheiro a monitorizar : \t ./cliente add \n");
        printf(" Para mostrar os ficheiros que estão a ser monitorizados :  ./cliente mostrar \n");
        printf(" Para sair do programa : \t                 ./cliente exit\n");
        printf("|------------------------------------------------------------------------|\n\n");
    }
    
    
    int main(int argc, char** argv) {
        int pipe = open("trabfifo", O_WRONLY);
        char *comando;
        if(argc < 2) printf("Invocação do programa cliente mal realizada!\n");
        else 
        {
            if(strncmp(argv[1],"add",strlen(argv[1]))==0)
              {
                   if(argc != 2) printf("O comando add foi mal invocado.\n Exemplo: ./cliente add n");    
                else
                {
                comando=juntarg(argv);
                write(pipe,comando,strlen(comando));
                }
            }
                else if(strncmp(argv[1],"mostrar",strlen(argv[1]))==0)
            {
                if(argc != 2) printf("O comando mostrar foi mal invocado.\n Exemplo: ./cliente mostrar n");
                else
                {
                    write(pipe,comando,strlen(comando)); 
                }
            }      
            else if(strncmp(argv[1],"help",strlen(argv[1])) == 0)
              {    
                  ajuda();          
              }     
              else printf("Comando Inexistente.\n");
            return 1;
            }
    }"
    And my server code is the following :

    Code:
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    
    
    int main(int argc, char** argv) {
    int pipe;
    char *comando;
    pipe=mkfifo("trabfifo",0646);
    open("trabfifo",O_RDONLY);
    read(pipe,comando,strlen(comando)-1); 
    printf("%s \n",comando);
    //close the pipe
    close(pipe);
    return 1;
    }"
    Any idea why it ain't working ?

    Thanks a lot.

  2. #2
    Registered User
    Join Date
    Jan 2009
    Posts
    1,485
    One thing I noticed is that commando is just an uninitialized pointer, so it does not make sense to read to it or use strlen on it.

  3. #3
    C Beginner
    Join Date
    Dec 2011
    Location
    Portugal
    Posts
    187
    How am I supposed to read it through the pipe then ?

  4. #4
    Registered User
    Join Date
    Jan 2009
    Posts
    1,485
    ? You read from your file descriptor called pipe, into memory at "comando", you read strlen(comando) -1 bytes.

    Now look at comando, it's just a pointer, it does not reference any memory you own. Using strlen on it is completely unpredictable because commando does not point to a string.

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Garbage appearing
    By DeanWinchester in forum C Programming
    Replies: 3
    Last Post: 05-27-2012, 03:47 PM
  2. include <iostream> appearing red
    By Tachimazu in forum C++ Programming
    Replies: 3
    Last Post: 06-21-2009, 11:59 PM
  3. Menu not appearing
    By P4R4N01D in forum Windows Programming
    Replies: 4
    Last Post: 02-13-2009, 10:27 PM
  4. Unwanted characters keep appearing
    By sundeeptuteja in forum C++ Programming
    Replies: 10
    Last Post: 03-01-2003, 12:58 AM
  5. CDialog actions after appearing
    By phil_drew in forum Windows Programming
    Replies: 0
    Last Post: 12-06-2002, 07:13 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21