VSCode C++ Intellisense can't discern C++20 features

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I try to run codes like

#include <string>
#include <iostream>

int main() {
    std::string str = "This is a string";
    std::cout << str.starts_with("name");
}

But intellisense will give out an error

"std::__cxx11::basic_string<char, std::char_traits, std::allocator>" has no member "starts_with" C/C++(135) [6,9]

And It still can be build and produce a correct result. Also it can find implementation in header file. But the macro __cplusplus is defined as 201703L I've already added a command -std=c++20 when building, why this happened?

Compiler: minGW 11.2 compiled by msys2

visual-studio-code c++20 c++
1 Answers

Assuming you are using Microsoft's C/C++ extension, you must configure the extension to use C++ 20 standard for intellisense.

The easiest way to do this is to add the line "C_Cpp.default.cppStandard": "c++20" to your settings.json file. You can also find the setting in the GUI under the name "Cpp Standard". Selecting c++20 from its dropdown will achieve the same result.

Note that this setting is, by default, set as a global user defaults. You can configure it per-workspace by selecting the Workspace tab in the settings GUI and changing that Cpp Standard dropdown to c++20.

As for why adding the -std=c++20 flag didn't work: -std=c++20 just tells your compiler which standard to use to build your code. 'Intellisense' does not receive this flag because it is a separate tool from the compiler and is therefore not required to support all the standards the compiler supports. It may support less even, although Intellisense tools usually support as current a standard as possible. Therefore the language standard for Intellisense must be configured separately from the compiler (in this case).

Final Note: After changing the setting, try closing and re-opening VS Code. In my experience changing the language standard setting can cause some weirdness to happen. Closing and re-opening VS Code seems to ensure the setting changes take full effect.

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