What I would like to do is to redirect stdout of some application, let say A to another application, let say B. All this from another external application (written in C).

Any ideas?

Do some research on pipes. Your system likely has a function you can call from C (popen, or similar) for opening a pipe based stream. Or, if you don't need access to the output from B, you can use the equivalent command line piping with the system function:

system ( "A | B" );

Thanks for your reply!
So, now I have:

fprintf(some_pipe, "%s", "some_input_text");

When I write "some_input_text" to some_pipe it then works on this input and produces the output, which is redirected to stdout (displayed on screen).

Is there any way to redirect it somewhere else, like local variable so I have access to it?

>Is there any way to redirect it somewhere else, like local variable so I have access to it?
Erm, you could use sprintf instead of fprintf to write to a string. But I'm not entirely sure how we got from "send the output of program A to program B from program C" to "write formatted output to a variable"...

>Is there any way to redirect it somewhere else, like local variable so I have access to it?
Erm, you could use sprintf instead of fprintf to write to a string. But I'm not entirely sure how we got from "send the output of program A to program B from program C" to "write formatted output to a variable"...

fprintf(some_pipe, "%s", "some_input_text");

"some_input_text" is an output read from pipe 'A' (which was in 'r' mode - to read from it), some_pipe is pipe 'B' (which was in 'w' mode - for write). Pipe A didn't have to have any 'input' to produce output, but pipe B did - unfortunately I also need the output of pipe B and I don't know how to create read/write pipe to make it work. I think there is some easier way for this...
I only wanted to put some data through a couple of 'sub-applications' and read the effects in some 'controlling application'...

>I don't know how to create read/write pipe to make it work.
Have you tried creating two pipes? One for input and one for output?

>I don't know how to create read/write pipe to make it work.
Have you tried creating two pipes? One for input and one for output?

I'm accually trying to do so, but I'm new to this stuff and It is not easy for me to understand how to use fork() and pipe() - which I think I should use...

> All this from another external application (written in C).
So is this application interested in any way as to what "A | B" does ?

Does it say
- collect the output of B
- get the exit status of A

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