work with fifo in c++ ( blocking read) - c++

Question

What I want to do :
1.Create and open for writing in.fifo by process1
2.Open in.fifo for reading in process2
3.Write from cin to in.fifo by process1 line
4.Read and cout line by process2
5.When input "exit" to cin (process2), it closed file in.fifo, delete it and exit
6.process2 exit, because in.fifo has no writer
In my programs process2 doesn't exit. In c it works with read,write when O_NONBLOCK is clear , but I want to do it in c++
write.cpp:
#include <stdlib.h>
#include <fstream>
#include <string>
#include <iostream>
using namespace std;
int main(){
std::ofstream fifo;
fifo.open("/home/fedor/projects/fifo2/in",ios::out);
if(! fifo.is_open() ){
std::cout << " error : cannot open file " << std :: endl;
return 1;
}
std::cout << " file open " << std :: endl;
std::string line;
while (line.compare("exit") != 0 ){
std::getline(cin, line);
fifo << line << endl;
/* do stuff with line */
}
fifo.close();
remove("/home/fedor/projects/fifo2/in");
return 0;
}
read.cpp:
#include <stdlib.h>
#include <fstream>
#include <string>
#include <iostream>
using namespace std;
int main(){
std::ifstream fifo;
fifo.open("/home/fedor/projects/fifo2/in",ifstream::in);
if(! fifo.is_open() ){
std::cout << " error : cannot open file " << std :: endl;
return 1;
}
std::cout << " file open " << std :: endl;
std::string line;
bool done = false;
while (!done)
{
while (std::getline(fifo, line))
{
cout << line << endl;
/* do stuff with line */
}
if (fifo.eof())
{
fifo.clear(); // Clear the EOF bit to enable further reading
}
else
{
done = true;
}
}
return 0;
}
I can't find where I can read about blocking read by streams like http://linux.die.net/man/3/read about blocking read
If process2 closed if input "exit", like process1 is that a life lock ? (Is it blocking on read, or just trying and trying to read )

Answer 1

There is no way to do what you want using C++ standard library, because in C++ there is no notion of processes and file sharing. You have to use OS-specific APIs, which most likely are C (like open()) but in theory they can be C++.

Answer 2

Your reader appears to explicitly ignore an eof, instead clearing the end of file condition, and continuing. You're saying that your reader isn't exiting. Of course it's not, you're explicitly clearing EOF and continuing. It's going to exit only on an error reading from the FIFO, which is going to be a fairly unusual event.
If you want to exit on an EOF, you'll have to explicitly do that. Or, if you want to terminate on receiving the exit message, your writer isn't going to send it. When the writer itself receives a typed "exit", it terminates without writing it to the fifo (and your reader needs to check for that).