Garbage appearing

[DeanWinchester]

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 :

#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 :

#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.

[Subsonics]

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.

[DeanWinchester]

How am I supposed to read it through the pipe then ?

[Subsonics]

? 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.