# Problem when trying to send a packet in UDP - SFML

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Hello eveyone
I'm trying to send some data from a server to a client but when the client receive that data its not the same data that i send, its different or corrupted somehow

[size="4"]Here what the server sends
Age: 12 Name: Bill Hight: 1.32f

Age: 52428 Name: -blank- Hight: -1.07374e+008

Why is that ?!!

here is the code

Server
 #include <SFML\Network.hpp> #include <iostream> struct PersonData { sf::Uint16 Age; std::string Name; float Height; }; sf::Packet& operator <<(sf::Packet& Packet, const PersonData& PD) { return Packet << PD.Age << PD.Name << PD.Height; } sf::Packet& operator >>(sf::Packet& Packet, PersonData& PD) { return Packet >> PD.Age >> PD.Name >> PD.Height; } void RunServer(unsigned short Port) { std::cout<<"write ip address of client you want to send data to "; std::string IP; std::cin >> IP; sf::IPAddress Address(IP); sf::SocketUDP Server; sf::Packet SendPacket; PersonData PersonData1 = {12, "Bill", 1.32f}; SendPacket >> PersonData1; if (Server.Send(SendPacket,IP ,Port) != sf::Socket::Done) { std::cout<<"Could not send data"; } } int main() { RunServer(4567); system("pause"); return 0; } 

Client
 #include <SFML\Network.hpp> #include <iostream> struct PersonData { sf::Uint16 Age; std::string Name; float Height; }; sf::Packet& operator <<(sf::Packet& Packet, const PersonData& PD) { return Packet << PD.Age << PD.Name << PD.Height; } sf::Packet& operator >>(sf::Packet& Packet, PersonData& PD) { return Packet >> PD.Age >> PD.Name >> PD.Height; } void RunClient() { sf::SocketUDP Client; if (!Client.Bind(4567)) { std::cout<<"Could not listen"; } sf::IPAddress Address; unsigned short Port; sf::Packet ReceivePacket; if (Client.Receive(ReceivePacket, Address, Port) != sf::Socket::Done) { std::cout<<"Could not Receive data"; } PersonData PersonData2; if (ReceivePacket << PersonData2) { std::cout << "Age: " << PersonData2.Age << "Name: " << PersonData2.Name << "Hight: "<< PersonData2.Height << std::endl; } Client.Close(); } int main() { RunClient(); system("pause"); return 0; } 

sorry for being a newbie and any help is much appreciated.

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if (ReceivePacket << PersonData2)

with

if (ReceivePacket >> PersonData2)

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hm.. I am not familiar with the library but I doubt you can send a structure with a "string" inside. I'd guess you need to replace it with a standard char array.

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if (ReceivePacket << PersonData2)

with

if (ReceivePacket >> PersonData2)

well that doesnt work, the client connect with the sever but no data get received from the server.

hm.. I am not familiar with the library but I doubt you can send a structure with a "string" inside. I'd guess you need to replace it with a standard char array.

yes you can send strings. even if you couldnt i still get weird numbers when i use float or int.

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I'm pretty sure you have your streaming operators the wrong way around.
When preparing a packet to send you do
sf::Packet SendPacket; PersonData PersonData1 = {12, "Bill", 1.32f}; SendPacket >> PersonData1;which creates an empty packet, then creates and initializes a PersonData structure and then writes the empty contents of the Packet over the just initialized PersonData.
What you want is
sf::Packet SendPacket; PersonData PersonData1 = {12, "Bill", 1.32f}; SendPacket << PersonData1;

Similarly, on the client side you do
PersonData PersonData2; if (ReceivePacket << PersonData2) { std::cout << "Age: " << PersonData2.Age << "Name: " << PersonData2.Name << "Hight: "<< PersonData2.Height << std::endl; }
which successfully creates an empty PersonData, writes the non-initialized contents into the packet and then prints the non-initialized values. You more likely want
PersonData PersonData2; if (ReceivePacket >> PersonData2) { std::cout << "Age: " << PersonData2.Age << "Name: " << PersonData2.Name << "Hight: "<< PersonData2.Height << std::endl; }

By the way, I dislike overloading the streaming operator for exactly this reason. It appears very intuitive, but it becomes a mess when two people think two different ways are intuitive. I prefer "Structure.Pack(Packet& Target)" and "Packet.Extract(Structure& Target)" structures because they say what they do in the name.

I hope that helps.

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I'm pretty sure you have your streaming operators the wrong way around.
When preparing a packet to send you do
sf::Packet SendPacket; PersonData PersonData1 = {12, "Bill", 1.32f}; SendPacket >> PersonData1;which creates an empty packet, then creates and initializes a PersonData structure and then writes the empty contents of the Packet over the just initialized PersonData.
What you want is
sf::Packet SendPacket; PersonData PersonData1 = {12, "Bill", 1.32f}; SendPacket << PersonData1;

Similarly, on the client side you do
PersonData PersonData2; if (ReceivePacket << PersonData2) { std::cout << "Age: " << PersonData2.Age << "Name: " << PersonData2.Name << "Hight: "<< PersonData2.Height << std::endl; }
which successfully creates an empty PersonData, writes the non-initialized contents into the packet and then prints the non-initialized values. You more likely want
PersonData PersonData2; if (ReceivePacket >> PersonData2) { std::cout << "Age: " << PersonData2.Age << "Name: " << PersonData2.Name << "Hight: "<< PersonData2.Height << std::endl; }

By the way, I dislike overloading the streaming operator for exactly this reason. It appears very intuitive, but it becomes a mess when two people think two different ways are intuitive. I prefer "Structure.Pack(Packet& Target)" and "Packet.Extract(Structure& Target)" structures because they say what they do in the name.

I hope that helps.

thankx for replaying.

yes i thought of that but the problem if i do that the client doesnt connect to the server at all, and when i run the client, the CMD just stays empty like its waiting for the server to connect. thats why i did it like this SendPacket >> PersonData1 . when i do it like this the client recivie data but its not correct data, which is very weird.

any other ideas

btw how do you this ( "Structure.Pack(Packet& Target)" and "Packet.Extract(Structure& Target)" structures ) i'm a newbie when it comes to networking, can you give me an example code that i can but in my program?

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thankx for replaying.

yes i thought of that but the problem if i do that the client doesnt connect to the server at all, and when i run the client, the CMD just stays empty like its waiting for the server to connect. thats why i did it like this SendPacket >> PersonData1 . when i do it like this the client recivie data but its not correct data, which is very weird.

any other ideas

btw how do you this ( "Structure.Pack(Packet& Target)" and "Packet.Extract(Structure& Target)" structures ) i'm a newbie when it comes to networking, can you give me an example code that i can but in my program?

I went to the tutorials page of SFML and downloaded the tutorial's source code. It has a small program in it that can run either as a server of client and shows you how to wait for a client to connect as a server and then check the server for new messages as a client. See the attached file. Refer to the tutorial and the documentation of SFML to see how the functions work. I actually have no idea. ;)

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I went to the tutorials page of SFML and downloaded the tutorial's source code. It has a small program in it that can run either as a server of client and shows you how to wait for a client to connect as a server and then check the server for new messages as a client. See the attached file. Refer to the tutorial and the documentation of SFML to see how the functions work. I actually have no idea. ;)

i have actully seen this and its using TCP connection. i have worked for the past 5 hours (not kidding) trying to modify it to work with UDP connection but it didnt work as i hoped. and i have posted the modified code which is the one i'm having problem with xD

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First make sure, that the right thing is sent.

Change the line for the server code from

SendPacket >> PersonData1;

to

SendPacket << PersonData1;

and verify with the debugger that everything is written as it should be.

Then when receiving make sure that you use the right operator, it must be

Packet >> Struct and not the other way round.

Your code looks quite ok except for the wrong operators.

Try it again with the right operators for both client and server and tell us what happens.

If you have problem, use the debbuger and maybe post the new code here.

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By the way, I dislike overloading the streaming operator for exactly this reason.

The order of operators is also undefined per standard. So one would need to do this:{ Packet p; p << a; p << b; p << c; return p; } // or (((p << a) << b) << c); // not sure if this works 
I don't know if there are compilers that don't respect expected left-to-right evaluation.

Overloading operators this way is not a problem per se, it's even idiomatic and falls in line with function overloading. Added benefit is that it can be seamlessly piped to any iostream, perhaps for debugging or logging, useful for third-party libraries.

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