Let us say I've written this C++ program (that essentially is doing nothing)
#include <cstdlib>
int main(int argc, char *argv[]) {
enum class Color { Red, Orange, Yellow, Green, Blue, Violet };
constexpr float a = 3.1415f;
auto b = a;
return EXIT_SUCCESS;
}
Is there a way to detect which C++11 features that are used in my program? Is there maybe some other program that could extract this information out of my source code? Such a program could output a list of features:
$ cat main.cc | some-clever-software
N2347
N1984
N2235
(Alternatively it could output URL:s http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1984.pdf instead)
If I had such a list it would be easier to write a CMakeLists.txt that makes use of the CMake command target_compile_features(), such as this one
cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)
project(foobar CXX)
add_executable(foobar main.cc)
set(needed_features
cxx_strong_enums
cxx_constexpr
cxx_auto_type)
target_compile_features(foobar PRIVATE ${needed_features})
The C++11 features that CMake let us choose from are listed in the CMake variable CMAKE_CXX_KNOWN_FEATURES. I know that the CMake command target_compile_features() has not yet been released in a stable CMake release. It currently lives in the development branch so it might come to change in the future. But nevertheless I'm interested if it is possible to detect what C++11 features are used in some C++ source code.
Update:
Compiling without the -std=c++11 compiler option was suggested in a comment:
First compiling with g++
$ g++ --version
g++ (Ubuntu/Linaro 4.8.1-10ubuntu9) 4.8.1
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ g++ main.cc
main.cc: In function ‘int main(int, char**)’:
main.cc:4:3: warning: scoped enums only available with -std=c++11 or -std=gnu++11 [enabled by default]
enum class Color { Red, Orange, Yellow, Green, Blue, Violet };
^
main.cc:5:3: error: ‘constexpr’ was not declared in this scope
constexpr float a = 3.1415f;
^
main.cc:5:13: error: expected ‘;’ before ‘float’
constexpr float a = 3.1415f;
^
main.cc:6:8: error: ‘b’ does not name a type
auto b = a;
^
and then compiling with clang
$ clang --version
Debian clang version 3.2-7ubuntu1 (tags/RELEASE_32/final) (based on LLVM 3.2)
Target: x86_64-pc-linux-gnu
Thread model: posix
$ clang main.cc
main.cc:4:8: error: expected identifier or '{'
enum class Color { Red, Orange, Yellow, Green, Blue, Violet };
^
main.cc:4:3: warning: declaration does not declare anything [-Wmissing-declarations]
enum class Color { Red, Orange, Yellow, Green, Blue, Violet };
^~~~
main.cc:5:3: error: unknown type name 'constexpr'
constexpr float a = 3.1415f;
^
main.cc:5:13: error: expected unqualified-id
constexpr float a = 3.1415f;
^
main.cc:6:3: warning: 'auto' type specifier is a C++11 extension [-Wc++11-extensions]
auto b = a;
^
main.cc:6:12: error: use of undeclared identifier 'a'
auto b = a;
^
2 warnings and 4 errors generated.
$
Of course, the diagnostics from the compilers give me good hints of which C++11 features that are in use. But what I would like to have is more fine-grained information:
N2235
instead of
error: ‘constexpr’ was not declared in this scope
