Thread: Working with pipes in C.

I'm currently looking at pipes as a way to open an audio file in a program I am working on.

For example:

Code:

FILE *bgmusic

bgmusic = popen(player filename.ext | aplay -f S16_LE -r 32000 -c 2", "r");

Calling pclose(bgmusic); will not work until I send a line feed to the pipe in order to stop the music as it runs on a continuous loop.

Now my question is what would be the best way to send a line feed to the pipe?

that looks like great code I dont see a problem

pclose() performs a wait4() on the process forked by popen(), however the process will not terminiate until a line feed has been sent to it, which puts me in a bit of a spot as I am rather new to pipes and not sure if you can communicate with it intermediately.

wait4() is telling it to wait for a return value (0) before it closes the stream, but until the line feed is sent, my music program sends a continuous loop to aplay.

Originally Posted by RemmyLee

Now my question is what would be the best way to send a line feed to the pipe?

There is no way to do that using popen(). The communication is one-way. In this case because you are reading, you cannot also write. You must either resort to a non-portable technique (popen() isn't very portable to begin with), or try to figure out a way to cause the "player" program to not require you to press the enter key.

Does the man page give an option to disable the looping?

It's actually a little player I wrote myself wrapped around the openspc library which permits interpretation of SPC700 sound files on a PC. It sends the converted output to stdout where aplay was grabbing it. The format was intended to loop continuously, so I tried to implement it that way.

Thanks for the info. I am completely new to pipes and was taking the lazy way out by using it. I'll just take a look at aplay's source and see if I can't hack together something that uses it directly to avoid the problem. Thanks again for the info.

Originally Posted by RemmyLee

It's actually a little player I wrote myself wrapped around the openspc library which permits interpretation of SPC700 sound files on a PC. It sends the converted output to stdout where aplay was grabbing it. The format was intended to loop continuously, so I tried to implement it that way.

If it's a program you control, you could add a program option which tells it not to loop. Then pass this option when you call it inside popen().