Suppose I have a program that, in part, runs another program using FILE *outptr=popen("some command string","r") and then fread()'s that program's stdout from outptr. Now, if that other program reads its input from its stdin, and I want that input to come from file inputfile already on disk, then I could easily just write FILE *outptr=popen("cat inputfile|otherpgm","r");
But here's the rub: rather than some inputfile on disk, my program has an internal unsigned char buffer[9999] which is what I want piped to otherpgm, but which I don't want written to disk first. How can I get buffer[] piped directly to otherpgm's stdin using popen()? Or some other mechanism, as long as I can read otherpgm's stdout from within my program.
CodePudding user response：
How can I get buffer[] piped directly to otherpgm's stdin using popen()?
This can't be done using popen.
Or some other mechanism
You need to set up two pipes (see man pipe) -- one from your-program to the other-program, and one from other-program to your-program, then fork, close appropriate ends of the pipes in the child and exec other-program.
You also need to worry about deadlocks if the data you need to write or read exceeds PIPE_BUF.
Relevant answer -- this can be much easier if you can make a FIFO on disk.
Another answer with examples.