Convertion from std::string to char?!
Author
Is it possible to convert from std::string to char somehow?! Because casting doesn't work, and I need it to be able to use the recv() function in WinSock. The recv() function takes a buffer parameter that's specified to be a char [or a char array], and there's no way of recieveing the correct amount of data on the server side unless I make about 50 different char arrays with different sizes or redimentionalize the char array buffer all the time, which I don't know how to do. Is there a way to do that? I would prefer to be able to convert from std::string to char somehow, though.
Quote:Original post by Wixner
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That won't work, he need a non-const array. He might be able to cast the constness away, but I expect that could introduce some problems. The best approach would be to recieve in an actual char array and then construct a std::basic_string from the char array. If there is a way to get the exact size needed you can construct a char buffer at the exact size.
About how to use the char array and resize it, to create a char string which you can give a new length, you do like this:
char* str = new char[strlen("Hello") + 1];strcpy(str,"Hello");Then later you can do like this:
delete [] str; // yes, you need this or a memory leak will occur.str = new char[201]; // We now needs 200 charsThis will completely empty the str so you need to copy it to a temporary string before deleting it if you still need it.
Quote:Original post by Afr0m@n
ARGH the lag!
Do I really need a non constant array?! Hmm.. I'll investigate. Thanks!
I haven't used this function myself, but as far as I can see you can set a max number of bytes to recieve, so if you have:
char InBuffer[50];
You can just set max number of bytes to recieve to 50, then you add InBuffer to a std::string or std::stringstream before calling recv again. Something like this:
char in[100];std::stringstream SS;do{ int ReturnValue = recv(the_socket,in,100,SomeFlags); if(ReturnValue == SOCKET_ERROR) return false; SS << in;}while( ReturnValue >= 100 ); // If there is no more to recieve less than 100 bytes have been recieved
Author
Thanks for your input guys! So far, nothing's worked. I'm really intrigued by your proposition though, RDragon1. How would I use a vector like that? Here's my code so far:
This results in these errors:
I've included <string> in another header file, so I don't get most of these errors.
#include "Global.h"bool AccountLogIn(int id, SOCKET s){ JPlayer p; std::vector<char> vec( str.begin(), str.end()); p.id = id; recv(s,(char*) vec, 100, MSG_PEEK); std::cout << vec; if(vec == "ACCOUNTEXISTS") { std::cout << "Recieved message!"; } return true;}This results in these errors:
--------------------Configuration: Server - Win32 Debug--------------------Compiling...AccountLogIn.cppC:\Programs\C++\WinSock\Server\AccountLogIn.cpp(6) : error C2039: 'vector' : is not a member of 'std'C:\Programs\C++\WinSock\Server\AccountLogIn.cpp(6) : error C2065: 'vector' : undeclared identifierC:\Programs\C++\WinSock\Server\AccountLogIn.cpp(6) : error C2062: type 'char' unexpectedC:\Programs\C++\WinSock\Server\AccountLogIn.cpp(10) : error C2065: 'vec' : undeclared identifierC:\Programs\C++\WinSock\Server\AccountLogIn.cpp(12) : error C2446: '==' : no conversion from 'char *' to 'int' This conversion requires a reinterpret_cast, a C-style cast or function-style castC:\Programs\C++\WinSock\Server\AccountLogIn.cpp(12) : error C2040: '==' : 'int' differs in levels of indirection from 'char [14]'Error executing cl.exe.Server.exe - 6 error(s), 0 warning(s)I've included <string> in another header file, so I don't get most of these errors.
use std::vector<char> like this:
You code would then become:
std::vector<char> buffer;buffer.resize(/*whatever size you want the buffer to be*/);//Now to get a char* of the buffer:char* buffer_ptr = &buffer[0];//and to convert to a std::stringstd::string asString(buffer.begin(),buffer.end());You code would then become:
#include <vector>#include <string>/* the rest of your code */bool AccountLogIn(int id, SOCKET s){ JPlayer p; std::vector<char> vec(100);//buffer of size 100 p.id = id; int bytes_recieved = recv(s,(char*) vec, 100, MSG_PEEK); std::string recieved_message(&vec[0], &vec[bytes_recieved]); if(recieved_message == "ACCOUNTEXISTS") { std::cout << "Recieved message!"; } return true;}This topic is closed to new replies.
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