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Under OS X 10.9.5 using XCode 6.0.1 I am running into the following issue when I try to run make from the terminal:

fatal error: 'wchar.h' file not found
This issue was not happening prior to a recent upgrade to Mavericks.
                Hello from Google. This is the answer you're probably looking for if you upgraded to Mojave recently.
– Qix - MONICA WAS MISTREATED
                Jan 29, 2019 at 20:00
First ensure that the latest XCode is installed. Next, we need to install/fix/update Command Line Tools. To do so, run
xcode-select --install
Previously, XCode expected it's active developer directory to be located at
/Applications/Xcode.app/Contents/Developer/
but the latest Command Line Tools is installed to
/Library/Developer/CommandLineTools/
so we need to switch where XCode is looking. To do so, run
sudo xcode-select --switch /Library/Developer/CommandLineTools/
And that should be it. These steps solved the issue for myself and two coworkers.
                Does not work for me. I can see that wchar.h file is located on /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/wchar.h and it should be found. There is no such file in command line tools folder (and deeper there)
– Euphorbium
                Sep 21, 2017 at 9:52
                I had the same problem, but with string.h  The solution for me was to delete "by hand" (with Finder) all output directories. The problem was that some old output files referenced out-of-date XCode paths. After I deleted all the output files, the problem was solved
– peter70
                Jun 18, 2018 at 14:10
                @peter70 Where are the output files you're referring to located? I encountered this issue with a Qt build, and I have no idea where to start looking for those output files.
– Piotr99
                Sep 26, 2018 at 9:52
                @Piotr99 If I remember correctly, they were the normal output files, in the output directory I specified (in Qt Projects Build Settings)
– peter70
                Oct 4, 2018 at 6:57
My error was similar to yours which said string.h not found, I solved it by running this command:
open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
I think that the problem is that for macOS Mojave users, the headers are no longer installed under /usr/include by default.
                No Packages folder under /Library/Developer/CommandLineTools/.only have following folders Library, SDKs and usr
– Wenmin Wu
                Jan 8, 2021 at 16:57
Adding on ssell's post and peter70's comment, I also still had issues after installing xcode command line tools again, and switching the xcode active developer directory.  I was using CMake, and so deleted the debug/release folders which had existing Makefiles referencing out-of-date locations on Mojave.  So for future problem resolving, after running the commands from ssell's post:
xcode-select --install
sudo xcode-select --switch /Library/Developer/CommandLineTools/
I believe if you've installed the command line tools by installing Xcode itself, you may also need to agree to the licence with sudo xcodebuild --license.  I don't think this is necessary if you used the prior xcode-select command.
Then also delete generated build scripts.  If using CMake, delete the cmake-build-debug and cmake-build-release directories (your names may vary)
Deleting all the generated files and restarted the compilation worked for me. It was suggested in this link:
https://discourse.brew.sh/t/solved-scan-build-from-llvm-7-0-seems-broken-on-macos-mojave/3151/14
                Works for me! (Here is my case: seems that I firstly let cmake generated those files (months ago), then update the mac version, then try to make / cmake again.)
– ch271828n
                Dec 20, 2020 at 3:11
                Regenerating from CMake and then ninja was not enough. Deleting the CMake-generated files also worked for me. I guess mine were too old. I wish CMake were smart enough to delete the old cache.
– Daniel Ryan
                Jan 25 at 0:59
                Works for me! (Here is my case: seems that I firstly let cmake generated those files (months ago), then update the mac version, then try to make / cmake again.)
– ch271828n
                Dec 20, 2020 at 3:11
xcode-select --install worked for me.
additionally if you're using visual studio code and your intellisense acts weird - 
make a folder called .vscode in your project root.
install vscode extension call C/C++ by microsoft 
create the c_cpp_properties.json file and paste the below contents
project_dir > .vscode > c_cpp_properties.json
    "configurations": [
        "name": "macOS",
        "includePath": ["${workspaceFolder}/**"],
        "defines": [],
        "macFrameworkPath": ["/System/Library/Frameworks", "/Library/Frameworks"],
        "compilerPath": "/usr/bin/clang",
        "cStandard": "c11",
        "cppStandard": "c++17",
        "intelliSenseMode": "${default}"
    "version": 4
If it happened after update Xcode you need (Apple WTF?) download and install Command Line Tools for Xcode manually from https://developer.apple.com/download/more/?=for%20Xcode
Or using terminal
xcode-select --install
Restart and maybe clean build cache (delete cmake-build-debug) before run your project.
I guess it's needed every time after update Xcode for all major program update
The issue is that the path of compiler gets changed after update or other advancement maybe xcode reinstallment.
I have tried everything that was given on every site sadly none worked.
I figured out that many issues cause this .
But then what worked for me is unlinking gcc.
I had also installed gcc from homebrew earlier.
Just unlinking it worked for me.
So if you are also one of the few who has installed gcc from homebrew then
brew unlink gcc
should be sufficient to get it off your default path, so you'll be back to Xcode's default gcc (assuming you have that installed).
        
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