first program

phil123 · 02-23-2004, 01:27 AM

the first program is real-time output program, how "my program" real-time read the redirect output from "first program"? loop read the argv[1]?can somebody write a simple code in follow... thanks

acid_kewpie · 02-23-2004, 02:59 AM

pleas explain your query in a more coherent manner... and provide more real details, what language are you using etc...

phil123 · 02-23-2004, 01:42 PM

the "first program" realtime output pixel data to standardout, I wish "my program" can dealwith these pixel data then output to standardout.
I use c++ on Red hat 9.0.
the problem is I am not sure how to realtime read these input data. How to open and read the pipe, " | ", in my program? just read argv[1]? how to ensure realtime.

chewysplace · 02-23-2004, 02:44 PM

#1: what "standardout" are you using? are you outputing to a file? to the screen? where is the output going?

#2: have you thought about combining the code to make one program that does all this?

#3: how is you pipe, "|", defined? what is your pipes purpose in the program? does it process input, output or both?

phil123 · 02-23-2004, 02:57 PM

1, the stdout points screen
2, i wish it can combin in one program, but "first program" should be any specifed file, no source code. I once use this way:
dup2(fds[0],stdout_fileno);
execlp("first program","first program", NULL);

however, it cannot work. I think the reason is firt program take place the current program. Do you have idea to do the output redirecting in proram.
3,"|" points shell command redirecting. you know, I try to use shell comand to do the above work.

chewysplace · 02-23-2004, 06:32 PM

i think you might be confused as to what stdout deals with. here is a link that better explains the usage of stdout with many extra references:
http://www.wlug.org.nz/stdout(3)

So "first program" is not realy a program at all, it's just a file?
If "first program" is just a file name, try setting a character string to it:

#include<string.h>

char FileName[256];
strcpy(FileName,"first program");

using FileName[256] allows you to copy another file name over if "first program" is not the file you wish to use anymore.

Something for you to play with:

#include<string.h>
#include<stdio.h>
#include<stdlib.h>
int main(int argv, char argc)
{
char *shellCommand = "xterm";
system(shellCommand);
}

This executes an XTerminal. You can change the shellCommand to what ever you need. Maybe make a whole bunch of pointers to shell commands. Then use a case statement to decide what command needs to be used.

Enjoy

itsme86 · 02-24-2004, 03:35 PM

In the '<first program> | <my program>' example, the output from <first program> is sent to <my program> through stdin.

So to read the output from <first program> you'd write your program something like this:

Code:

int main(void)
{
  char *buf = NULL, inp[256];
  int size = 0, n;

  while(fgets(inp, sizeof(inp), stdin))
  {
    n = strlen(inp);
    size += n;
    buf = realloc(buf, size+1);
    memcpy(buf+size, inp, n);
  }

  // 'buf' now holds all of the output from <first program>
}

phil123 · 02-25-2004, 02:35 AM

I also can get from argv[1].