winsock, sending c++ style strings

b00l34n · 04-23-2004, 02:39 PM

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, 02:44 PM

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

Speedy5 · 04-23-2004, 03:10 PM

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, 03:33 PM

i already tried that, it didn't work?

**Salem** · 04-23-2004, 03:46 PM

Post your code

b00l34n · 04-24-2004, 06:00 AM

the code is really really long...

bennyandthejets · 04-24-2004, 06:31 AM

Post the part that gives you the error.

b00l34n · 04-24-2004, 08:04 AM

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, 08:06 AM

Code:

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

b00l34n · 04-24-2004, 08:36 AM

already tried that, still got the error

b00l34n · 04-24-2004, 08:39 AM

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, 09:04 AM

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

b00l34n · 04-24-2004, 09:08 AM

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, 09:13 AM

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, 09:26 AM

> 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';
}

04-23-2004, 02:39 PM	#1
b00l34n Registered User Join Date: Apr 2004 Posts: 102	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?
b00l34n is offline

04-23-2004, 02:44 PM	#2
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	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. Up to 8Mb PlusNet broadband from only £5.99 a month!
Salem is offline

04-23-2004, 03:10 PM	#3
Speedy5 Registered User Join Date: Jan 2003 Posts: 648	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.
Speedy5 is offline

04-23-2004, 03:33 PM	#4
b00l34n Registered User Join Date: Apr 2004 Posts: 102	i already tried that, it didn't work?
b00l34n is offline

04-23-2004, 03:46 PM	#5
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	Post your code __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut. Up to 8Mb PlusNet broadband from only £5.99 a month!
Salem is offline

04-24-2004, 06:00 AM	#6
b00l34n Registered User Join Date: Apr 2004 Posts: 102	the code is really really long...
b00l34n is offline

04-24-2004, 06:31 AM	#7
bennyandthejets mustang benny Join Date: Jul 2002 Posts: 1,401	Post the part that gives you the error. __________________ benforbes@optusnet.com.au Microsoft Visual Studio .NET 2003 Enterprise Architect Windows XP Pro Code Tags Programming FAQ Tutorials
bennyandthejets is offline

04-24-2004, 08:06 AM	#9
Speedy5 Registered User Join Date: Jan 2003 Posts: 648	Code: send(clientSocket, outMessage.c_str(), sizeof(outMessage.c_str()), 0);
Speedy5 is offline

04-24-2004, 08:36 AM	#10
b00l34n Registered User Join Date: Apr 2004 Posts: 102	already tried that, still got the error
b00l34n is offline

04-24-2004, 08:39 AM	#11
b00l34n Registered User Join Date: Apr 2004 Posts: 102	ohh, im very sorry, i didn't see the brackets, i feel stupid now... but yes it works perfectly now. thankyou very much
b00l34n is offline

04-24-2004, 09:04 AM	#12
HybridM Grammar Police Join Date: Jan 2003 Posts: 355	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. OS: Windows XP Compiler: MSVC
HybridM is offline

04-24-2004, 09:08 AM	#13
b00l34n Registered User Join Date: Apr 2004 Posts: 102	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?
b00l34n is offline

04-24-2004, 09:13 AM	#14
HybridM Grammar Police Join Date: Jan 2003 Posts: 355	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
HybridM is offline

04-24-2004, 09:26 AM	#15
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	> 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. Up to 8Mb PlusNet broadband from only £5.99 a month!
Salem is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Programming using strings	jlu0418	C++ Programming	5	11-26-2006 08:07 PM
Problems with strings as key in STL maps	all_names_taken	C++ Programming	3	01-17-2006 11:34 AM
Winsock Messaging Program	Morgul	Windows Programming	13	04-25-2005 04:00 PM
Where do I initialize Winsock and catch messages for it?	Lithorien	Windows Programming	10	12-30-2004 12:11 PM
array of strings + more	null	C Programming	10	10-01-2001 03:39 PM