C++ -std=... default of various commonly used C++ compilers

Compiler	Version	__cplusplus
g++	4.7.4	199711L
	5.5.0	199711L
	6.1.0	201402L
	10.2	201402L
	11.1.0	201703L
clang++	3.4.2	199711L
	5.0.0	199711L
	6.0.0	201402L
	12.0.1	201402L
	16.0.0	201703L
hipcc	4.0.0	201103L
	4.1.0	201103L
icpc	15.0.2	199711L
	17.0.2	199711L
	18.0.1	201402L
	21.1.1	201402L
icpc (classic/oneAPI)	2021.1 Beta 20200602	201402L
	2021.6.0	201402L
	2021.7.0	201703L
	21.5.0	201402L
icpx (oneAPI)	2021.1.2	201402L
	2022.2.1	201402L
dpcpp	2021.1-beta07 (2020.5.0.0604)	201703L
	2022.0.0 (2022.0.0.20211123)	201703L
pgc++	16.1	199711L
	17.5	199711L
	18.3	201402L
nvc++	22.7	201703L
xlc++	14.1b2	199711L
(XLClang)	16.1.1	199711L
crayc++ (classic)	8.7.9	201402L
crayc++ (LLVM)	9.0.0	201402L
msvc	19.28	199711L
	19.28	199711L
	19.35	199711L

Note: MSVC __cplusplus defines are unreliable.
Note: For Clang++, the -x hip|cuda frontend default differs from -x c++ for older releases.

Meaning of __cplusplus

__cplusplus	C++ Standard
199711L	C++98
201103L	C++11
201402L	C++14
201703L	C++17
202002L	C++20
TBD	C++23

Meaning of __STDC_VERSION__

Random fun fact: The C standard for C-compilers defines a similar macro, __STDC_VERSION__:

__STDC_VERSION__	C Standard
undefined	earlier
199409L	C95
199901L	C99
201112L	C11
201710L	C18
TBD	C23

Default of various commonly used C compilers

Compiler	Version	__STDC_VERSION__
gcc	4.9.4	undefined
	5.1.0	201112L
	8.1	201710L
clang	3.0.0	199901L
	3.5.2	199901L
	3.6	201112L
	11.0	201710L
icc (classic/oneAPI)	21.1.9	201112L
icx (oneAPI)	2021.1.2	201710L

References

Inspired by https://stackoverflow.com/a/44735016/2719194

$CXX -dM -E -x c++  /dev/null | grep -F __cplusplus

or just check if this C++14 snippet compiles and read its assembly:

struct X {
    static constexpr int value = __cplusplus;
};

int main() {
    auto const x = X::value;
    return 0;
}

Equivalently for C:

cc -dM -E -x c  /dev/null | grep -F __STDC_VERSION__

or in code:

#include <stdio.h>

int main(){
    printf("%ld", __STDC_VERSION__);
}