Fflush does not write buffered text - c

Question

I'm trying to print a 2D table to my terminal using this code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <termios.h>
#include <sys/wait.h>
char getch()
{
char ch;
struct termios old, new;
tcgetattr(0, &old); // grab old terminal i/o settings
new = old; // new settings = old settings
new.c_lflag &= ~ICANON; // disable buffered i/o
new.c_lflag &= ~ECHO; //set echo mode
tcsetattr(0, TCSANOW, &new); // use these new terminal i/o settings now
ch = getchar();
tcsetattr(0, TCSANOW, &old); //restore old settings
return ch;
}
void readPBM(char *output)
{
char tmp[1024];
int fd[2] = {0,0};
int pid;
//Open the pipe for inter-process communication
pipe(&fd[0]);
//Fork and test if we are child or parent process
pid = fork();
if(pid) //Parent process
{
wait(NULL); //Wait for child's end
close(fd[1]);//Close pipe's write stream
close(0);//Close stdin
dup(fd[0]);//Duplicate stdout
close(fd[0]);//Close old stdout
strcpy(output, "");// Init output at 0
while(fgets(tmp, 1024, stdin) != NULL) //Put remaining entry in output
{
strcat(output, tmp);
}
}
else if(pid == 0) //Child process
{
close(fd[0]);//Close pipe's read stream
close(1);//Close stdout
dup(fd[1]);//Duplicate stdin
close(fd[1]);//Close old stdin
printf("A random string ...\n");
}
else //Print error if fork failed
{
printf("Error creating a new process");
exit(EXIT_FAILURE);
}
}
int main(int argc, char *argv[])
{
int i, j;
char *str = NULL;
char c;
str = malloc(512 * sizeof(char*));
readPBM(str);
printf("%s", str);
fflush(stdout);
c = getch();
}
I have a UNIX implementation of getch().
My problem is that my program is waiting for an input to print the table. I tried to fflush(stdout) and to disable terminal buffering with ICANON but it's still not working.
PS: it's not working neither with getchar, scanf, ...
EDIT: So I came up to this minimal example; it seems to be pipe-related.

Answer 1

My problem is that my program is waiting for an input to print the table.
This is because you forgot to terminate the child process when it has done its work, so after printing A random string ... to the pipe it continues, returning from readPBM() and eventually executing the c = getch() at the end of main(). The remedy is to call exit(0) at the end of the if(pid == 0) //Child process block.