winsock, sending c++ style strings

This is a discussion on winsock, sending c++ style strings within the Networking/Device Communication forums, part of the General Programming Boards category; hello!, you may remember i posted a while back about a winsock chat program.. anyway, i have encountered another problem. ...

  1. #1
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    winsock, sending c++ style strings

    hello!, you may remember i posted a while back about a winsock chat program..
    anyway, i have encountered another problem. i can send C style strings (char str[]) but when trying to send a c++ style string (string str) i get errors, why?

    error C2664: 'send' : cannot convert parameter 2 from 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<c
    har> >' to 'const char *'
    No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
    Error executing cl.exe.

    now i don't know what this is saying...
    i know i could just convert the string every time i needed to send it, but that would be messy...

    any ideas?

  2. #2
    and the hat of wrongness Salem's Avatar
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    Why not use
    mystring.c_str()
    to get at the const char * version of the string?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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    Its expecting a C-string (char *), not a C++ std::string object. Like Salem said, use that method to get the C-string from the string object.

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    i already tried that, it didn't work?

  5. #5
    and the hat of wrongness Salem's Avatar
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    Post your code
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    the code is really really long...

  7. #7
    mustang benny bennyandthejets's Avatar
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    Post the part that gives you the error.
    benforbes@optusnet.com.au
    Microsoft Visual Studio .NET 2003 Enterprise Architect
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    Code:
    string outMessage;
    getline(cin,outMessage);
    iferror = send(clientSocket, outMessage.c_str, sizeof(outMessage), 0);
    		
    if (iferror == SOCKET_ERROR) {
    cout << "Send Failed\n";
    shutdownServer(clientSocket);
    }
    i have just pulled out the parts of the code that could possibly cause the error.

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    Code:
    send(clientSocket, outMessage.c_str(), sizeof(outMessage.c_str()), 0);

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    already tried that, still got the error

  11. #11
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    ohh, im very sorry, i didn't see the brackets, i feel stupid now... but yes it works perfectly now.
    thankyou very much

  12. #12
    Grammar Police HybridM's Avatar
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    the c_str() member of the std::string class is a function, so it needs brackets.
    Thor's self help tip:
    Maybe a neighbor is tossing leaf clippings on your lawn, looking at your woman, or harboring desires regarding your longboat. You enslave his children, set his house on fire. He shall not bother you again.

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    yes i forgot,
    im now getting errors using the same method for:

    Code:
    recv(clientSocket, inMessage.c_str(), sizeof(inMessage.c_str()), 0);
    error:

    error C2664: 'recv' : cannot convert parameter 2 from 'const char *' to 'char *'
    Conversion loses qualifiers

    is there a solution?

  14. #14
    Grammar Police HybridM's Avatar
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    the recv() function acts differently to send()

    What you will need to do is create a temporary c-style string buffer, use that in the call to recv() and then copy the c-string into your std::string.

    Code:
    std::string Buf;
    char tempBuf[256] = "";
    
           BytesRecv = recv(Socket, tempBuf, 256, 0);
    
           if(strcmp("", tempBuf))
                  Buf = tempBuf;
    Thor's self help tip:
    Maybe a neighbor is tossing leaf clippings on your lawn, looking at your woman, or harboring desires regarding your longboat. You enslave his children, set his house on fire. He shall not bother you again.

    OS: Windows XP
    Compiler: MSVC

  15. #15
    and the hat of wrongness Salem's Avatar
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    > sizeof(inMessage.c_str())
    Shouldn't this be
    strlen(inMessage.c_str())

    > BytesRecv = recv(Socket, tempBuf, 256, 0);
    You need to allow room for appending a \0, and actually add a \0 as well
    Code:
    BytesRecv = recv(Socket, tempBuf, sizeof(tempBuf)-1, 0);
    if ( BytesRecv > 0 ) {
        tempBuf[BytesRecv] = '\0';
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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