assert in constexpr function

Question

In trying to work out why I was getting a certain compile error, I came up with the following minimal example:

constexpr void Test(bool test)
{
    if (test)
        return;

    assert(false);
}

This compiles without issue with every version of clang I tried (3.7+), but fails with gcc (tested 5-8), with

error: call to non-‘constexpr’ function ‘void __assert_fail(const char*, const char*, unsigned int, const char*)’

From my understanding, the function should be able to be constexpr because there is a set of argument values for which the function can be evaluated at compile time.

Is my understanding wrong, or is gcc incorrect in failing to compile this?

Similar to Throw in constexpr function bugs there are part of gcc constexpr metabug — Shafik Yaghmour
– Shafik Yaghmour, Commented Sep 19, 2018 at 7:50

cpplearner · Accepted Answer · 2018-09-19 04:16:05Z

7

This is GCC bug 86678, and was fixed just a few days ago.

answered Sep 19, 2018 at 4:16

cpplearner

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Comments

jpihl · Accepted Answer · 2021-02-19 08:09:19Z

0

If you like me have this issue, but you can't upgrade the compiler nor change the code. A quick fix is to have the compiler remove the asserts by adding the NDEBUG flag to the compiler:

gcc/clang: -DNDEBUG
msvc: /DNDEBUG

Maybe this can save someone a bit of time.

answered Feb 19, 2021 at 8:09

jpihl

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