GCC 7 cannot compile example files (C++20 features needed)

[baptistepillot]

Hello,

I wrote so few C++ in my life... I am a beginner here and I would like to get a "from scratch" compilation procedure for this project.
Someone has it ?

Here is my procedure (Linux Mint 19.3), but the compilation crashes :

sudo apt install gcc
# Mint 19.3 embeds gcc-7, which is fully C++ 17 compatible, in theory.
# tried the same with gcc-10, but still not working. I may miss some library.
mkdir web-server
cd web-server
git clone https://github.com/uNetworking/uWebSockets
git submodule init
git submodule update
make

This results in this log, full of errors :

make -C uSockets; \
for FILE in HelloWorld EchoServer BroadcastingEchoServer UpgradeSync UpgradeAsync; do g++ -flto -O3 -lpthread -Wconversion -std=c++17 -Isrc -IuSockets/src examples/$FILE.cpp -o $FILE uSockets/*.o -lz & done; \
for FILE in HelloWorldThreaded EchoServerThreaded; do g++ -pthread -flto -O3 -lpthread -Wconversion -std=c++17 -Isrc -IuSockets/src examples/$FILE.cpp -o $FILE uSockets/*.o -lz & done; \
wait
make[1] : on entre dans le répertoire « /home/baptiste/gcc/web-server/uWebSockets/uSockets »
rm -f *.o
cc -DLIBUS_NO_SSL -std=c11 -Isrc -flto -O3 -c src/*.c src/eventing/*.c src/crypto/*.c
ar rvs uSockets.a *.o
r - context.o
r - epoll_kqueue.o
r - gcd.o
r - libuv.o
r - loop.o
r - openssl.o
r - socket.o
r - wolfssl.o
make[1] : on quitte le répertoire « /home/baptiste/gcc/web-server/uWebSockets/uSockets »
examples/EchoServerThreaded.cpp: In lambda function:
examples/EchoServerThreaded.cpp:43:14: error: no matching function for call to ‘uWS::TemplatedApp<false>::ws<main()::PerSocketData>(const char [3], <brace-enclosed initializer list>)’
             }).listen(9001, [](auto *token) {
              ^
In file included from examples/EchoServerThreaded.cpp:1:0:
src/App.h:99:20: note: candidate: template<class UserData> uWS::TemplatedApp<SSL>&& uWS::TemplatedApp<SSL>::ws(std::__cxx11::string, uWS::TemplatedApp<SSL>::WebSocketBehavior&&) [with UserData = UserData; bool SSL = false]
     TemplatedApp &&ws(std::string pattern, WebSocketBehavior &&behavior) {
                    ^~
src/App.h:99:20: note:   template argument deduction/substitution failed:
examples/EchoServerThreaded.cpp:43:14: note:   cannot convert ‘{SHARED_COMPRESSOR, (16 * 1024), 10, ((1 * 1024) * 1024), <lambda closure object>main()::<lambda(std::thread*)>::<lambda()>::<lambda(auto:11*)>{}, <lambda closure object>main()::<lambda(std::thread*)>::<lambda()>::<lambda(auto:12*, std::string_view, uWS::OpCode)>{}, <lambda closure object>main()::<lambda(std::thread*)>::<lambda()>::<lambda(auto:13*)>{}, <lambda closure object>main()::<lambda(std::thread*)>::<lambda()>::<lambda(auto:14*)>{}, <lambda closure object>main()::<lambda(std::thread*)>::<lambda()>::<lambda(auto:15*)>{}, <lambda closure object>main()::<lambda(std::thread*)>::<lambda()>::<lambda(auto:16*, int, std::string_view)>{}}’ (type ‘<brace-enclosed initializer list>’) to type ‘uWS::TemplatedApp<false>::WebSocketBehavior&&’
             }).listen(9001, [](auto *token) {
              ^
examples/BroadcastingEchoServer.cpp: In function ‘int main()’:
examples/BroadcastingEchoServer.cpp:46:6: error: no matching function for call to ‘uWS::TemplatedApp<false>::ws<main()::PerSocketData>(const char [3], <brace-enclosed initializer list>)’
     }).listen(9001, [](auto *token) {
      ^
In file included from examples/BroadcastingEchoServer.cpp:1:0:
src/App.h:99:20: note: candidate: template<class UserData> uWS::TemplatedApp<SSL>&& uWS::TemplatedApp<SSL>::ws(std::__cxx11::string, uWS::TemplatedApp<SSL>::WebSocketBehavior&&) [with UserData = UserData; bool SSL = false]
     TemplatedApp &&ws(std::string pattern, WebSocketBehavior &&behavior) {
                    ^~
src/App.h:99:20: note:   template argument deduction/substitution failed:
examples/BroadcastingEchoServer.cpp:46:6: note:   cannot convert ‘{SHARED_COMPRESSOR, ((16 * 1024) * 1024), 10, ((1 * 1024) * 1024), <lambda closure object>main()::<lambda(auto:11*)>{}, <lambda closure object>main()::<lambda(auto:12*, std::string_view, uWS::OpCode)>{}, <lambda closure object>main()::<lambda(auto:13*)>{}, <lambda closure object>main()::<lambda(auto:14*)>{}, <lambda closure object>main()::<lambda(auto:15*)>{}, <lambda closure object>main()::<lambda(auto:16*, int, std::string_view)>{}}’ (type ‘<brace-enclosed initializer list>’) to type ‘uWS::TemplatedApp<false>::WebSocketBehavior&&’
     }).listen(9001, [](auto *token) {
      ^
examples/EchoServer.cpp: In function ‘int main()’:
examples/EchoServer.cpp:45:6: error: no matching function for call to ‘uWS::TemplatedApp<true>::ws<main()::PerSocketData>(const char [3], <brace-enclosed initializer list>)’
     }).listen(9001, [](auto *token) {
      ^
In file included from examples/EchoServer.cpp:2:0:
src/App.h:99:20: note: candidate: template<class UserData> uWS::TemplatedApp<SSL>&& uWS::TemplatedApp<SSL>::ws(std::__cxx11::string, uWS::TemplatedApp<SSL>::WebSocketBehavior&&) [with UserData = UserData; bool SSL = true]
     TemplatedApp &&ws(std::string pattern, WebSocketBehavior &&behavior) {
                    ^~
src/App.h:99:20: note:   template argument deduction/substitution failed:
examples/EchoServer.cpp:45:6: note:   cannot convert ‘{SHARED_COMPRESSOR, (16 * 1024), 10, ((1 * 1024) * 1024), <lambda closure object>main()::<lambda(auto:11*)>{}, <lambda closure object>main()::<lambda(auto:12*, std::string_view, uWS::OpCode)>{}, <lambda closure object>main()::<lambda(auto:13*)>{}, <lambda closure object>main()::<lambda(auto:14*)>{}, <lambda closure object>main()::<lambda(auto:15*)>{}, <lambda closure object>main()::<lambda(auto:16*, int, std::string_view)>{}}’ (type ‘<brace-enclosed initializer list>’) to type ‘uWS::TemplatedApp<true>::WebSocketBehavior&&’
     }).listen(9001, [](auto *token) {
      ^

Sorry for this, this is I am sure a really noob question. Everyone has to start one day. (btw I am an experienced web developer, just a noob in building c++ programming infrastructure).

[baptistepillot]

Well, only the compilation of the Echo application crash : I got a working HelloWorld and HelloWorldThreaded apps (and Update...), so I suppose it works well, only the "echo" demo apps miss something.

[ghost]

Hello, I think the examples require C++20 but the library itself does not. So you probably need GCC9 or Clang10. You can always write the examples in C++17 but then they look less "declarative".

[Kelvin-Weksa]

does anyone have the examples written in c++17? I can't seem to figure it out how to replace the designated inits

[Kelvin-Weksa]

because even this doesn't work. exact same error. compiler still thinks its a damn [brace-enclosed initializes list]

uWS::SSLApp({
        /* There are example certificates in uWebSockets.js repo */
	    .key_file_name = "../misc/key.pem",
	    .cert_file_name = "../misc/cert.pem",
	    .passphrase = "1234"
	}).ws<PerSocketData>("/*", {
        /* Settings */
        /*.compression = */uWS::SHARED_COMPRESSOR,
        /*.maxPayloadLength = */16 * 1024 * 1024,
        /*.idleTimeout = */16,
        /*.maxBackpressure = */1 * 1024 * 1024,
        /*.closeOnBackpressureLimit = */false,
        /*.resetIdleTimeoutOnSend = */false,
        /*.sendPingsAutomatically = */true,

        /* Handlers */
        /*.upgrade = */nullptr,
        /*.open = */[](auto */*ws*/) {
            /* Open event here, you may access ws->getUserData() which points to a PerSocketData struct */
        },
        /*.message = */[](auto *ws, std::string_view message, uWS::OpCode opCode) {
            ws->send(message, opCode, true);
        },
        /*.drain = */[](auto */*ws*/) {
            /* Check ws->getBufferedAmount() here */
        },
        /*.ping = */[](auto */*ws*/, std::string_view) {
            /* Not implemented yet */
        },
        /*.pong = */[](auto */*ws*/, std::string_view) {
            /* Not implemented yet */
        },
        /*.close = */[](auto */*ws*/, int /*code*/, std::string_view /*message*/) {
            /* You may access ws->getUserData() here */
        }
    }).listen(9001, [](auto *listen_socket) {
        if (listen_socket) {
            std::cout << "Listening on port " << 9001 << std::endl;
        }
    }).run();```

[ghost]

Don't try to shove everything in one go - create an explicit WebSocketBehavior struct and initialize it row by row so that you see what is wrong.

[Kelvin-Weksa]

turns out had to add .maxLifetime = 0, at correct order (same order as definition) to make it work
so the working one is

uWS::SSLApp({
        /* There are example certificates in uWebSockets.js repo */
	    .key_file_name = "../misc/key.pem",
	    .cert_file_name = "../misc/cert.pem",
	    .passphrase = "1234"
	}).ws<PerSocketData>("/*", {
        /* Settings */
        .compression = uWS::SHARED_COMPRESSOR,
        .maxPayloadLength = 16 * 1024 * 1024,
        .idleTimeout = 16,
        .maxBackpressure = 1 * 1024 * 1024,
        .closeOnBackpressureLimit = false,
        .resetIdleTimeoutOnSend = false,
        .sendPingsAutomatically = true,
        .maxLifetime = 0,
        /* Handlers */
        .upgrade = nullptr,
        .open = [](auto */*ws*/) {
            /* Open event here, you may access ws->getUserData() which points to a PerSocketData struct */
        },
        .message = [](auto *ws, std::string_view message, uWS::OpCode opCode) {
            ws->send(message, opCode, true);
        },
        .drain = [](auto */*ws*/) {
            /* Check ws->getBufferedAmount() here */
        },
        .ping = [](auto */*ws*/, std::string_view) {
            /* Not implemented yet */
        },
        .pong = [](auto */*ws*/, std::string_view) {
            /* Not implemented yet */
        },
        .close = [](auto */*ws*/, int /*code*/, std::string_view /*message*/) {
            /* You may access ws->getUserData() here */
        }
    }).listen(9001, [](auto *listen_socket) {
        if (listen_socket) {
            std::cout << "Listening on port " << 9001 << std::endl;
        }
    }).run();

[ghost]

Designated initializers could use a lot better diagnostics in the compilers, however they are very new so that will probably come with time.

[baptistepillot]

I tried with GCC10, which fully supports C++20. Only the "ECHO" examples does not work, so I do not matter. The other examples work well, and, YES!, I developed my first c++ web server in 1 hour.

EDIT : Confusion : GCC is the C compiler. I need G++, the C++ compiler, version 9 or better. Ok : I try it !

[baptistepillot]

Ok : Just installed G++-10 (https://askubuntu.com/questions/1192955/how-to-install-g-10-on-ubuntu-18-04) and all examples work well !

Thanks a lot.

[baptistepillot]

Here is an "hello world" application example, with all the instructions to make it run from Debian / Ubuntu systems. I will check it on a newly installed debian / ubuntu / mint distro, this could help noobs like me to know how to use it starting from nothing :
https://github.com/itrocks/cpp

[ghost]

Alright. I try to stay as far away from building instructions as possible but I guess I could cover the need for C++20 a bit better.