C language help actually

[rugged dawn]

is there anyone that can help me with understanding popen and pclose in C I am having a hard time understanding them from the man page
:(

[lyric pewter]

int main(void){
  FILE* const pipe = popen("cat /path/to/a/file", "r");
  // normal read operation as with a file
  pclose(pipe);
}

obviously if you to write to that pipe instead you'd use "w" as the second argument

[rugged dawn]

what's the use of popen why not use pipe with an fd as usual

also should the path to a file be any file or a fifo?

[lyric pewter]

this function is higher level

you don't to explicitly call pipe, and fork

that's the advantage

the path is just an example because i used catas an example

you can use any other command

[rugged dawn]

ohh

lets say I want to pass a message from parent to a child process can u give me a psuedo code or code for it

[lyric pewter]

is the child process an external command?

[sonic flax]

what is people using pipe for? shared memory?

[rugged dawn]

also if I interpreted the above code correctly pipe holds the file pointer for path with read permission

[lyric pewter]

interprocess communication

[rugged dawn]

yeah sure

[sonic flax]

can u give example

client-client communication?

like a c++ project to another C++ project

[lyric pewter]

not path, it's a wrapper around the read-end of the pipe

i used cat, but it could just be ls for example

[rugged dawn]

yeah read-end got it

I see

[lyric pewter]

have you ever run a unix command with piping?

[rugged dawn]

|

[lyric pewter]

yeah

processes can communicate via pipes but they must be somehow "related" (either "siblings" or "father-son" relationship)

[sonic flax]

nope

[lyric pewter]

also communication is unidirectional

[rugged dawn]

ping me if u do this

[rugged dawn]

half duplex

[lyric pewter]

$ ls -1 my-directory | grep '\.jpg'

[sonic flax]

like what is that code for

[lyric pewter]

i mean, the code i posted above is pretty much that

it consists of two processes

ls lists the contents of a directory

grep is essentially a filter command

the | is the pipe operator interpreted by your shell

so, the output of ls, which would normally be printed to the terminal is fed into grep's stdin

and grep will only print entries which contain the string '.jpg'

[lyric pewter]

int main(void){
  FILE* const pipe = popen("some command that will read from stdin", "w");
  fwrite("abc", 3, 1, pipe);
  pclose(pipe);
}

i dont remember if this is how you use fwrite