Piping between processes, using pipes, using low level read() and write()

This is a discussion on Piping between processes, using pipes, using low level read() and write() within the Linux Programming forums, part of the Platform Specific Boards category; Okay.. Here is the deal I have multiple processes. I have a unistd.h pipe open, and one end is a ...

  1. #1
    Rebooted Inquirer's Avatar
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    Piping between processes, using pipes, using low level read() and write()

    Okay.. Here is the deal

    I have multiple processes. I have a unistd.h pipe open, and one end is a file descriptor (int fd1) and the other is stored in another int (int fd2). Unfortunately, these are ints, so i can't use fread, fwrite, etc, or fputs, fputc. I have been looking around for read and write, but haven't found anything about their usage, just comments that something is a wrapper for it or something. Does anyone know how to use these, or if there is a readline that will do more than one character? same for writeline, if there is one. Also, what is the prototype and return value of it. If there is a website that will help explain these to me, that works just as well. Thanks a ton!

    ~Eko
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    GCC on Mac OS X 10.2.4 (Secondary)

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  2. #2
    Obsessed with C chrismiceli's Avatar
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    are you talking about unbuffered i/o?
    try this
    Code:
    write(fd1, buf, sizeof buf);
    memset(&buf, 0, sizeof buf); /* so we know it wasn't just left over */
    read(fd2, buf, sizeof buf);
    puts(buf);
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    Rebooted Inquirer's Avatar
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    yeah, unbeffered io... that means nothing to me. I i have tried (the equivalent of) what you showed me, but it still doesn't work. I'm trying varius means of debugging it, to make sure its looking in the right file descriptors, etc, but could you explain what unbuffered io is? does that mean that it has to be waiting to read while it sends for it to be read? or what? I'm too used to C++ streams =/

    ~Eko
    Compilers:
    GCC on Red Hat 8.1 (Primary)
    GCC on Mac OS X 10.2.4 (Secondary)

    Others:
    MinGW on XP

  4. #4
    Obsessed with C chrismiceli's Avatar
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    unbuffered i/o means it sends one at a time, the kernel does not buffer it in some sort of buffer. If you were to write a message, say "message", the kernel would send 'm', wait until it is finished with that, then send 'e' and so on. buffered i/o, the kernel buffers it, so if you sent the same "message", they kernel would probably cache all of it then send the whole thing to be read. Can you show us some code?
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    Just Lurking Dave_Sinkula's Avatar
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    Re: Piping between processes, using pipes, using low level read() and write()

    Originally posted by Inquirer
    I have a unistd.h pipe open, and one end is a file descriptor (int fd1) and the other is stored in another int (int fd2). Unfortunately, these are ints, so i can't use fread, fwrite, etc, or fputs, fputc. I have been looking around for read and write, but haven't found anything about their usage, just comments that something is a wrapper for it or something. Does anyone know how to use these, or if there is a readline that will do more than one character? same for writeline, if there is one. Also, what is the prototype and return value of it. If there is a website that will help explain these to me, that works just as well. Thanks a ton!
    read
    write


    Could fdopen make life easier?
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