More Pipes

• FILE *popen(const char *command, const char *type);
  • This is a shortcut for communicating with another process.
  • This will
    • Set up a pipe
      • if type is "r" the current process is on the read end of the pipe.
      • If type is "w" the current process is on the write end.
      • I know that type is a const char * but this is c for string.
    • Fork
    • exec command
    • And return a c style file stream (FILE *) , or NULL if something fails.
  • The process can then read or write from/to the stream.
• int pclose(FILE *stream);
  • Close the pipe
  • Wait for the child to exit.
  • Return the exit status.
  • or -1 on error.
• There are more details, but these will do for now.
• Look at popenRead.cpp and popenWrite.cpp.
• int mkfifo(const char *pathname, mode_t mode);
  • The arguments are much like open.
  • This builds the file on the system which is an interface to a pipe.
  • This overcomes the problem that the pipe must be shared between two related processes.
  • We have already worked with these.
  • Open will block for read only or write only until the other end is opened.
• Look at dieServer.cpp and dieClient.cpp
• int unlink(const char *pathname);
  • removes the file.
  • But only if this is the last link to the file.
  • And no processes have the file open.
    • The file will be removed after these exit.