read/write a floating point value

This is a discussion on read/write a floating point value within the Networking/Device Communication forums, part of the General Programming Boards category; Hi Im currently writing a server/client system. I use c++ on the server and java on the client. Therefore I ...

  1. #1
    Registered User
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    Apr 2003
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    3

    read/write a floating point value

    Hi

    Im currently writing a server/client system. I use c++ on the server and java on the client.

    Therefore I want to write a protocol that handles the byte orders and other communication issues. For example to write a integer onto the socket stream, I do like this:


    Code:
    void writeInt(int i)
    {
       write(socket, (void*)((i >> 24) & 0xff), sizeof(char));
       write(socket, (void*)((i >> 16) & 0xff), sizeof(char));
       write(socket, (void*)((i >> 8) & 0xff), sizeof(char));
       write(socket, (void*)(i  & 0xff), sizeof(char));
    }
    This would convert it from little-endian to big-endian. So this works. The problem is if I want to write/read a float or a double. First of all, you can't use the shift operator on a floating-point value. I know on java they have readDouble & writeDouble functions in the DataInput/DataOutput interfaces. I think that the writeDouble function are implemented in a way that they convert the double to a long and then write it over the network. And the readDouble converts it back again.

    Maybe I have to do something similar. I know I have to do some bit manipulation, but I don't know what. The problem with java approach, is of course that the size of a long is 4 bytes on the linux box(c++), but on the client(java) it is 8 bytes. So I might have deal with that problem as well.

    Anyone who have struggled with something similar?. I will be very thankfull for any help.

    Thanks

  2. #2
    End Of Line Hammer's Avatar
    Join Date
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    Write the numbers to the socket in plain text, with a terminator of some sort. Like:

    123.987\0 (\0 being a 0x00 byte)

    Then use the other ends string to number conversion routines.

    There are functions for doing to bit manipulation for longs etc :
    http://www.rt.com/man/htonl.3.html
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  3. #3
    Registered User
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    Apr 2003
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    Yeh that would of course be a solution to the problem.
    I will try that out.

    Thanks

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