change function

Discussion in 'C++' started by Larry, Jan 29, 2010.

  1. Larry

    Larry Guest

    Hi,

    I would like to turn this function:

    std::string Socket::ReceiveBytes() {
    std::string ret;
    char buf[1024];

    while (1) {
    u_long arg = 0;
    if (ioctlsocket(s_, FIONREAD, &arg) != 0)
    break;

    if (arg == 0)
    break;

    if (arg > 1024) arg = 1024;

    int rv = recv (s_, buf, arg, 0);
    if (rv <= 0) break;

    std::string t;

    t.assign (buf, rv);
    ret += t;
    }

    return ret;
    }

    into something like:

    bool Socket::ReceiveBytes(char * buffer, const int buffersize);

    how should I change it internally?

    thanks
     
    Larry, Jan 29, 2010
    #1
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  2. Larry

    Larry Guest

    "Larry" <> ha scritto nel messaggio
    news:4b635ddc$0$1137$...

    > into something like:


    this is what I have figure out so far: (untested)


    #include <algorithm>

    int Socket::ReceiveBytes(char * buffer, int buffersize)
    {
    if(buffersize > 32768)
    buffersize = 32768;

    char temp[32768];
    int byrv = 0;

    while (1)
    {
    u_long arg = 0;

    if (ioctlsocket(s_, FIONREAD, &arg) != 0)
    return -1;

    if (arg == 0)
    return byrv;

    if (arg > buffersize)
    arg = buffersize;

    int rv = recv (s_, temp, arg, 0);

    if (rv <= 0)
    return -1;

    std::copy(temp, temp + rv, buffer);
    byrv += rv;
    }
    }
     
    Larry, Jan 29, 2010
    #2
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  3. Larry

    Larry Guest

    "Larry" <> ha scritto nel messaggio
    news:4b637617$0$820$...

    > this is what I have figure out so far: (untested)


    #include <algorithm>

    int Socket::ReceiveBytes(char * buffer, int buffersize)
    {
    if(buffersize > 32768)
    buffersize = 32768;

    char temp[32768];

    u_long arg = 0;

    if (ioctlsocket(s_, FIONREAD, &arg) != 0)
    return -1;

    if (arg == 0)
    return 0;

    if (arg > buffersize)
    arg = buffersize;

    int rv = recv (s_, temp, arg, 0);

    if (rv <= 0)
    return -1;

    if (rv == 0)
    return 0;

    if (rv > 0)
    std::copy(temp, temp + rv, buffer);

    }

    where FIONREAD:

    Determine the amount of data which can be read atomically from socket s.
    argp points to an unsigned long in which ioctlsocket stores the result. If s
    is stream oriented (for example, type SOCK_STREAM), FIONREAD returns an
    amount of data which can be read in a single recv; this may or may not be
    the same as the total amount of data queued on the socket. If s is message
    oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the
    first datagram (message) queued on the socket.

    So I basically I will recv according to ioctlsocket. if the latter is > then
    buffersize I will read buffersize (arg = buffersize) if it's
    less...well...be just happy with that...if it's 0 or less don't even bother
    copying the buffer and return accordingly.

    that's all

    what about my idea?

    thanks
     
    Larry, Jan 30, 2010
    #3
  4. Larry

    Larry Guest

    "Larry" <> ha scritto nel messaggio
    news:4b637617$0$820$...

    > this is what I have figure out so far: (untested)


    #include <algorithm>

    int Socket::ReceiveBytes(char * buffer, int buffersize)
    {
    if(buffersize > 32768)
    buffersize = 32768;

    char temp[32768];

    u_long arg = 0;

    if (ioctlsocket(s_, FIONREAD, &arg) != 0)
    return -1;

    if (arg == 0)
    return 0;

    if (arg > buffersize)
    arg = buffersize;

    int rv = recv (s_, temp, arg, 0);

    if (rv <= 0)
    return -1;

    if (rv == 0)
    return 0;

    if (rv > 0)
    std::copy(temp, temp + rv, buffer);

    }

    where FIONREAD:

    Determine the amount of data which can be read atomically from socket s.
    argp points to an unsigned long in which ioctlsocket stores the result. If s
    is stream oriented (for example, type SOCK_STREAM), FIONREAD returns an
    amount of data which can be read in a single recv; this may or may not be
    the same as the total amount of data queued on the socket. If s is message
    oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the
    first datagram (message) queued on the socket.

    So I basically I will recv according to ioctlsocket. if the latter is > then
    buffersize I will read buffersize (arg = buffersize) if it's
    less...well...be just happy with that...if it's 0 or less don't even bother
    copying the buffer and return accordingly.

    that's all

    what about my idea?

    thanks
     
    Larry, Jan 30, 2010
    #4
  5. Larry

    Jorgen Grahn Guest

    On Sat, 2010-01-30, Larry wrote:
    > "Larry" <> ha scritto nel messaggio
    > news:4b637617$0$820$...
    >
    >> this is what I have figure out so far: (untested)

    >
    > #include <algorithm>
    >
    > int Socket::ReceiveBytes(char * buffer, int buffersize)
    > {
    > if(buffersize > 32768)
    > buffersize = 32768;
    >
    > char temp[32768];
    >
    > u_long arg = 0;
    >
    > if (ioctlsocket(s_, FIONREAD, &arg) != 0)
    > return -1;
    >
    > if (arg == 0)
    > return 0;
    >
    > if (arg > buffersize)
    > arg = buffersize;
    >
    > int rv = recv (s_, temp, arg, 0);
    >
    > if (rv <= 0)
    > return -1;
    >
    > if (rv == 0)
    > return 0;
    >
    > if (rv > 0)
    > std::copy(temp, temp + rv, buffer);
    >
    > }


    Try compiling it with full warnings enabled before posting -- I spot
    at least one compile error. Also please indent with more that 1 space
    -- 4 is rather universal.

    > where FIONREAD:
    >
    > Determine the amount of data which can be read atomically from socket s.
    > argp points to an unsigned long in which ioctlsocket stores the result. If s
    > is stream oriented (for example, type SOCK_STREAM), FIONREAD returns an
    > amount of data which can be read in a single recv; this may or may not be
    > the same as the total amount of data queued on the socket. If s is message
    > oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the
    > first datagram (message) queued on the socket.


    It's not clear if you expect your socket to be stream or datagram. Or
    what you intend the function to do. It's unusual, I think, to user the
    same high-level function for both.

    Adding just a tiny bit of documentation would have helped when
    discussing it, a lot.

    I don't think it's very common for people to use FIONREAD, by the way.
    I think there are better options ... but I don't remember exactly and
    it's offtopic here anyway.

    > So I basically I will recv according to ioctlsocket. if the latter is > then
    > buffersize I will read buffersize (arg = buffersize) if it's
    > less...well...be just happy with that...if it's 0 or less don't even bother
    > copying the buffer and return accordingly.
    >
    > that's all
    >
    > what about my idea?


    One thing I don't understand is the extra copying. You went from a
    std::string to a char* of known length, but why not read straight into
    it?

    /Jorgen

    --
    // Jorgen Grahn <grahn@ Oo o. . .
    \X/ snipabacken.se> O o .
     
    Jorgen Grahn, Feb 3, 2010
    #5
  6. Larry

    tonydee Guest

    Re: change function

    On Jan 30, 7:14 am, "Larry" <> wrote:
    > Hi,
    >
    >   I would like to turn this function:
    >
    > std::string Socket::ReceiveBytes() {
    >   std::string ret;
    >   char buf[1024];
    >
    >   while (1) {
    >     u_long arg = 0;
    >     if (ioctlsocket(s_, FIONREAD, &arg) != 0)
    >       break;
    >
    >     if (arg == 0)
    >       break;
    >
    >     if (arg > 1024) arg = 1024;
    >
    >     int rv = recv (s_, buf, arg, 0);
    >     if (rv <= 0) break;
    >
    >     std::string t;
    >
    >     t.assign (buf, rv);
    >     ret += t;
    >   }
    >
    >   return ret;
    >
    > }
    >
    > into something like:
    >
    > bool Socket::ReceiveBytes(char * buffer, const int buffersize);
    >
    > how should I change it internally?
    >
    > thanks


    I think you're making this a lot more complicated than it need be.
    The existing recv() or read() functions provide almost this interface
    already. If you want to avoid them blocking when no input is
    available, set the socket to nonblocking mode before calling them -
    you only need do that once instead of checking before every recv().

    Cheers,
    Tony
     
    tonydee, Feb 4, 2010
    #6
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