VSCode cannot detect C++ system files when clangd is enabled

Question

For example, if I include <string>, it will show an error saying 'string' file not found clang(pp_file_not_found):

I am building the project into build folder. And use a .clangd file to specify the CompilationDatabase to where compile_commands.json is. This method is successful in my another PC(macOS). For VScode settings about clangd, I specified the clangd.path.

For this PC(Linux Ubuntu), I tried to add "-std=c++17" to 'clangd.fallbackflags'. But it still does not work.

When I use CMake to compile the whole project, it works well. Seems it is a VSCode issue or clangd issue.

Update: I found that if I use #include <9/string> instead of #include <string>, vscode can find the file, is that something about include path? However, I have never made changes to it. So I tried to update the include path by this method Visual Studio Code cannot open source file "iostream". Still does not work.

did you follow the project setup instructions for the clangd extension? (I.e. put a compile commands database file in the workspace root? see also stackoverflow.com/q/76214615/11107541) — starball
– starball ♦, Commented Sep 7, 2023 at 7:08
Yes, I use CMake and use set(CMAKE_EXPORT_COMPILE_COMMANDS ON) to set. Also use .clangd file to specify the position of compile_commands.json. Also add "-std=c++17" to 'clangd.fallbackflags'. Still does not work. — jlx
– jlx, Commented Sep 7, 2023 at 7:28
okay, but is your build directory set to the source directory, then? (in-source build)? — starball
– starball ♦, Commented Sep 7, 2023 at 7:29
if you're building to a subdirectory of the source directory, then that is not an in-source build, and you need to follow the instructions in the post which I linked you to. — starball
– starball ♦, Commented Sep 7, 2023 at 7:34

HighCommander4 · Accepted Answer · 2023-09-09 05:30:08Z

You might be running into a known issue affecting Ubuntu 22.04: https://github.com/clangd/clangd/issues/1394.

You can read about the available workarounds in this comment, but this simplest one is to install g++-12.

If that's not the issue, my next suggestion is to read these parts of the clangd docs:

and try --query-driver in particular.

If you're still not having any luck, please share clangd logs for further diagnosis.

jlx · Accepted Answer · 2025-02-28 02:09:26Z

I solved this problem by adding missing libs:

sudo apt update sudo apt install clang clangd libclang-dev libstdc++-9-dev

Check the installation by:

echo | clang++ -E -x c++ - -v

Reinstall some libs if there is missing path or other issues:

sudo apt install --reinstall libstdc++-11-dev libstdc++-9-dev

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