Redirecting stdout to pipe in C - c

Question

Here's a program I'm trying to make:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char* argv[])
{
char* arguments[] = {"superabundantes.py", NULL};
int my_pipe[2];
if(pipe(my_pipe) == -1)
{
fprintf(stderr, "Error creating pipe\n");
}
pid_t child_id;
child_id = fork();
if(child_id == -1)
{
fprintf(stderr, "Fork error\n");
}
if(child_id == 0) // child process
{
close(my_pipe[0]); // child doesn't read
dup2(my_pipe[1], 1); // redirect stdout
execvp("cat", arguments);
fprintf(stderr, "Exec failed\n");
}
else
{
close(my_pipe[1]); // parent doesn't write
char reading_buf[1];
while(read(my_pipe[0], reading_buf, 1) > 0)
{
write(1, reading_buf, 1); // 1 -> stdout
}
close(my_pipe[0]);
wait();
}
}
I want to execute the exec in the child redirecting the stdout of the child to the parent (through the pipe). I think the problem might be related to dup2, but I haven't used it before.

Answer 1

You need to also provide argv[0] when you call exec. So your arguments should read:
char* arguments[] = {"cat", "superabundantes.py", NULL};

Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char* argv[])
{
//char* arguments[] = {"cat","tricky.txt", NULL};
char* arguments[] = {"./son1", NULL};
int my_pipe[2];
if(pipe(my_pipe) == -1)
{
fprintf(stderr, "Error creating pipe\n");
}
pid_t child_id;
child_id = fork();
if(child_id == -1)
{
fprintf(stderr, "Fork error\n");
}
if(child_id == 0) // child process
{
close(my_pipe[0]); // child doesn't read
dup2(my_pipe[1], 1); // redirect stdout
execvp(arguments[0], arguments);
fprintf(stderr, "Exec failed\n");
}
else
{
close(my_pipe[1]); // parent doesn't write
char reading_buf[1];
while(read(my_pipe[0], reading_buf, 1) > 0)
{
write(1, reading_buf, 1); // 1 -> stdout
}
close(my_pipe[0]);
wait();
}
}
/*
if ./son1 returns
printf() in son1 will be output by write(1 ..) in parent
if son1 is in dead loop then
printf() in son1 will NOT be output by write(1 ..) in parent
void main()
{
printf( "***** son run *****\n\r" );
return;
while(1);
}
any idea?
*/