Thread: Why child process will not read argv[2] past five characters?

Assignment almost finished aside from this little issue. Using poll because for some reason cygwin freezes without it. Parent process copies command line arguments to string and then sends it a character at a time to the child process, while counting, character by character and finally outputting the number of characters in the arguments.

I set i to 1 in loop control so that it ignores the first argument (the exe name of course).

It works fine as long as my first argument doesn't exceed 4 characters (any following arguments are counted just fine.) Any ideas?

Code:

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>         // for fork(), sleep()
#include <sys/wait.h>       // for waitpid()
#include <sys/poll.h>       // for poll()

static int      stop = 0;
static char     line[256];
static int      comm[2];



int main (int argc, char **argv)
{
    pid_t   pid;
    int     status;
	char ch;
	int nChars;
	
	    // set up pipe
    if (pipe(comm)) {
        printf("pipe error\n");
        return -1;
        }

    // fork into parent and child processes
    pid = fork();

    // fork() failed
    if (pid < 0) {
        printf("fork error %d\n", pid);
        return -1;
        }

    else if (pid == 0) {
        struct pollfd    pollSpec;
        close(comm[1]);         // child doesn't need output side 
        // set up to poll input end of pipe
        pollSpec.fd = comm[0];
        pollSpec.events = POLLIN;

		
		printf("child recieving: ");
        while ( poll(&pollSpec, 1, 1000)){
			read(comm[0], &ch, 1);				
			nChars++;				
			printf("%c", ch);    //print characters as child recieves them
			fflush(stdout); // override line buffering 
			sleep(1);// 1 second	
			}



                

            
		printf("\nchild: counted %d characters\n", nChars);
        close(comm[0]);

        printf("child exits\n");
        return 0;
	}

    //parent process
    else {
        close(comm[0]);   //parent doesn't need input side
        printf("parent waiting\n");
	int i, j;
	for(i = 1; i < argc; i++)
	{
		strcpy(line, argv[i]); //copy command line arguments to array
		for(j = 0; j < sizeof(argv[i]); j++)
		{			
			ch = line[j];
			if(ch != '\0'){

			write(comm[1], &ch, 1);  //send characters to child
			sleep(1);

			}

		}

	}	

        stop = 1;               // tell child to stop via global variable
       
		printf("parent tells child to stop\n");
        waitpid(pid, &status, 0);
        printf("parent reaps child status 0x%08X\n", status);
        if (WIFEXITED(status))
            printf("child exited normally with %d\n", WEXITSTATUS(status));
        close(comm[1]);
        printf("parent exits\n");
        return 0;
	}

}

sizeof(argv[i]) does not measure the length of the string argv[i], but is the size of the data type char* (usually 4).

Doh! strlen NOT sizeof... got it...There is no exit condition for my gratitude. Works great now...