winsock, sending c++ style strings

**b00l34n** · 04-23-2004

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?

**Salem** · 04-23-2004

Why not use
mystring.c_str()
to get at the const char * version of the string?

**Speedy5** · 04-23-2004

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.

**b00l34n** · 04-23-2004

i already tried that, it didn't work?

**Salem** · 04-23-2004

Post your code

**b00l34n** · 04-24-2004

the code is really really long...

**bennyandthejets** · 04-24-2004

Post the part that gives you the error.

**b00l34n** · 04-24-2004

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.

**Speedy5** · 04-24-2004

Code:

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

**b00l34n** · 04-24-2004

already tried that, still got the error

**b00l34n** · 04-24-2004

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

**HybridM** · 04-24-2004

the c_str() member of the std::string class is a function, so it needs brackets.

**b00l34n** · 04-24-2004

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?

**HybridM** · 04-24-2004

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;

**Salem** · 04-24-2004

> 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';
}

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