C++ code compiles with release build, fails with debug build (/D_DEBUG); MSVC obviously

Expectation: define _DEBUG (or switching between release and debug build) doesn’t change whether code is accepted; apparently Mircosoft has a different view...

// source code, x.cpp
#include <cstdio>
#include <string>

static constexpr std::string s = “asdf”;

int main() {
printf(“%s\n”, s.c_str());
}

Compile with debug:

cl /std:c++20 /D_DEBUG x.cpp
Microsoft ® C/C++ Optimizing Compiler Version 19.39.33520 for x64
Copyright © Microsoft Corporation. All rights reserved.

x.cpp
x.cpp(4): error C2131: expression did not evaluate to a constant
x.cpp(4): note: (sub-)object points to memory which was heap allocated during constant evaluation

Compile as release:

cl /std:c++20 x.cpp
Microsoft ® C/C++ Optimizing Compiler Version 19.39.33520 for x64
Copyright © Microsoft Corporation. All rights reserved.

x.cpp
Microsoft ® Incremental Linker Version 14.39.33520.0
Copyright © Microsoft Corporation. All rights reserved.

/out:x.exe
x.obj

Bonus: when the initializer string “asdf” is longer, e.g. “aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaasdf” also the release build fails (which is OK)

There's actually a very good and detailed technical explanation.

posted at: 10:00 | path: /programming | permanent link