在子进程中执行并发送到管道，结果导致无限循环

Question

I am doing this in a child process: execlp ("wc", "wc" ,filename,"-l", NULL) and redirecting the output in a pipe to read from father process.

All working good but when wc option doesn't find the specified file name it cause an infinite loop. Same thing with find option.

How can i check the output of execlp or what should i do to not get into this infinite loop?

this is the code from child created with fork:

close(1); 
if (dup (pipeCom[1]) != 1) 
{
 fprintf (stderr, "dup - 1\n");
 exit (1);  
}
execlp ("wc", "wc" ,filename,"-l", NULL);`

this is the code from parent process:

wait();
if ((num = read(pipeCom[0],&out,200))==0)   
perror("pipe error");   
else {
     out[num] = '\0';
     }
printf("%s",out);

Answer 1

Jonathan is absolutely right about dup2() and the position of the "-l" option. That being said, an SSCCE would be like this:

#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
        const char *filename = "/etc/passwd"; /* whatever */
        int pipeCom[2];
        char out[200];
        int num, status;
        if(pipe(pipeCom)) {
                perror("pipe");
                return 111;
        }
        if(argv[1])
                filename = argv[1];
        switch(fork()) {
        case -1:
                perror("fork");
                return 111;
        case 0:
                /* child */
                close(1);
                if (dup (pipeCom[1]) != 1)
                {
                        fprintf (stderr, "dup - 1\n");
                        exit (1);
                }
                execlp ("wc", "wc" ,filename,"-l", NULL); /* Jonathan! */
                perror("wc");
                return 111;

        default:
                /* parent */
                wait(&status);
                if ((num = read(pipeCom[0],&out,200))==0)
                        perror("pipe error");
                else {
                        out[num] = '\0';
                }
                printf("%s",out);
                break;
        }
        return 0;
}

Your original code wouldn't even compile because of wait() without parameters; simply fixing that led to a program that compiles and works on my system, so... Can you post exactly the piece of code that is giving you trouble, explaining exactly how you compile/run it and exactly what is failing? My guts tell me that filename==NULL in your case, but if that is the case, it would have been a lot better to read it in your program than to imagine it ;p