Linux build with GCC broken due to use of C++14 features

[purinchu]

I tried to build this library just now using CMake 3.10.0 and gcc 7.2.0 on a Linux system.

It failed to build, giving error messages of the form:

[12/167] Building CXX object src/CMakeFiles/cpprest.dir/uri/uri.cpp.o
FAILED: src/CMakeFiles/cpprest.dir/uri/uri.cpp.o 
/usr/lib/ccache/bin/c++  -DCPPREST_FORCE_HTTP_CLIENT_ASIO -DCPPREST_FORCE_HTTP_LISTENER_ASIO -Dcpprest_EXPORTS -I../include -I../src/pch -I../libs/websocketpp -std=c++11 -fno-strict-aliasing -O3 -DNDEBUG -fPIC   -Werror -pedantic -Wall -Wextra -Wunused-parameter -Wcast-align -Wcast-qual -Wconversion -Wformat=2 -Winit-self -Winvalid-pch -Wmissing-format-attribute -Wmissing-include-dirs -Wpacked -Wredundant-decls -Wunreachable-code -MD -MT src/CMakeFiles/cpprest.dir/uri/uri.cpp.o -MF src/CMakeFiles/cpprest.dir/uri/uri.cpp.o.d -o src/CMakeFiles/cpprest.dir/uri/uri.cpp.o -c ../src/uri/uri.cpp
In file included from ../src/pch/stdafx.h:99:0,
                 from ../src/uri/uri.cpp:14:
../include/pplx/pplxtasks.h:6702:79: error: ‘operator&&’ function uses ‘auto’ type specifier without trailing return type
 auto operator&&(const task<_ReturnType> & _Lhs, const task<_ReturnType> & _Rhs)
                                                                               ^
../include/pplx/pplxtasks.h:6702:79: note: deduced return type only available with -std=c++14 or -std=gnu++14

A fuller excerpt is attached at cpprestsdk-build-failure.log

The error message mentioned C++14 support being needed. I found that altering the base CMakeLists.txt to set -std=c++14 instead of its current c++11 mode when using GCC did indeed allow the library to build and link.

Poking around, it seems that the recent commit 09d5984 introduced the C++14-related changes, but I'm not sure if C++14 is supposed to be verboten or not.

[kinuthiaduncan]

setting -std=c++14 also worked for me

[ras0219-msft]

I've fixed this issue in master, thank you for reporting the problem!