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question about popen in C

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# 8  
Old 03-15-2011
Yes, that looks more like it.

I don't see that you've redirected stdout for the "w" case, so it'd go to the terminal as usual.
# 9  
Old 03-15-2011
Quote:
Originally Posted by omega666
and just to be clear again, when given 'w', the output of the string gets discarded or printed to stdout?
It depends on the caller's file descriptors and their flags.

Quote:
Originally Posted by popen opengroup documentation
The environment of the executed command shall be as if a child process were created within the popen() call using the fork() function, and the child invoked the sh utility using the call:
execl(shell path, "sh", "-c", command, (char *)0) where shell path is an unspecified pathname for the sh utility.
So, as usual with fork/exec, the child will inherit all of its parents file descriptors that are not marked close-on-exec (FD_CLOEXEC). Additionally, there's the possibility of redirections in the command passed to "sh".

Regards,
Alister
Last edited by alister; 03-15-2011 at 05:52 AM..
# 10  
Old 03-15-2011
Quote:
if (*type == "r") {
you are comparing a character(typically an integer) with a string (char *) . This is illegal, you should better try
Quote:
if (*type == 'r') {

Note the difference b/w "r" and 'r'.

There are other problems yet with the code.

Thanks,
Gaurav.
# 11  
Old 03-15-2011
i have another question
this is what i have
When given "r", the child process sets fd[1] to stdout and writes the result of the string to that end of the pipe, and closes both ends of the pipe, while the parent closes the write end and sends the read end back

But when given "w", i know that the result of the string gets printed to stdout, but i dont understand what to close in the child process... The child is just writing the result to stdout, so do I need a dup2 there? Can i close both ends of the pipe for the child? For the parent i think i just have to close the read end and return the write end. but i'm confused as to what to close for the child process...
Last edited by omega666; 03-17-2011 at 05:15 PM..
# 12  
Old 03-15-2011
You asked many questions but I don't know what are you trying.
Do you try to open a program and redirect both stdin and stdout?

I've got a function that does that pretty well, so if you are trying that ask me. If not, try to explain what are your objective.
# 13  
Old 03-15-2011
trying to make a function that does what popen does
# 14  
Old 03-15-2011
Spoiler:

Koders Code Search: popen.c - C - BSD

Check that, it might help you.
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