<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/116554>116554</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            `-nostdinc++` on Windows doesn't seem to work
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          BluTree
      </td>
    </tr>
</table>

<pre>
    I have a case where I want to disable C++ standard library includes, to only use system headers and C standard library as follows:
```cpp
#include <iostream>
#include <stdio.h>

int main(int argc, char** argv)
{
    printf("Hello World");

 return 0;
}
```
For this, I use `-nostdinc++` to have errors when including c++ headers (in this case, iostream).
But on Windows, this doesn't seem to change anything. When looking at the search paths by invoking clang with verbose output, I have these includes:
```
C:\Dev\Sources\C++ tests>clang++ src/test.cc -nostdinc++ -o test.exe --verbose
clang version 19.1.3
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Dev\LLVM\bin
 "C:\\Dev\\LLVM\\bin\\clang++.exe" -cc1 -triple x86_64-pc-windows-msvc19.41.34120 -emit-obj -mincremental-linker-compatible -dumpdir test.exe- -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name test.cc -mrelocation-model pic -pic-level 2 -mframe-pointer=none -relaxed-aliasing -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic "-fdebug-compilation-dir=C:\\Dev\\Sources\\C++ tests" -v "-fcoverage-compilation-dir=C:\\Dev\\Sources\\C++ tests" -nostdinc++ -resource-dir "C:\\Dev\\LLVM\\lib\\clang\\19" -internal-isystem "C:\\Dev\\LLVM\\lib\\clang\\19\\include" -internal-isystem "C:\\Dev\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\MSVC\\14.41.34120\\include" -internal-isystem "C:\\Dev\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\MSVC\\14.41.34120\\atlmfc\\include" -internal-isystem "C:\\Windows Kits\\10\\Include\\10.0.22621.0\\ucrt" -internal-isystem "C:\\Windows Kits\\10\\Include\\10.0.22621.0\\shared" -internal-isystem "C:\\Windows Kits\\10\\Include\\10.0.22621.0\\um" -internal-isystem "C:\\Windows Kits\\10\\Include\\10.0.22621.0\\winrt" -internal-isystem "C:\\Windows Kits\\10\\Include\\10.0.22621.0\\cppwinrt" -fdeprecated-macro -ferror-limit 19 -fmessage-length=175 -fno-use-cxa-atexit -fms-extensions -fms-compatibility -fms-compatibility-version=19.41.34120 -std=c++14 -fskip-odr-check-in-gmf -fdelayed-template-parsing -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -o "C:\\Users\\Aubin\\AppData\\Local\\Temp\\test-91f9da.o" -x c++ src/test.cc
clang -cc1 version 19.1.3 based upon LLVM 19.1.3 default target x86_64-pc-windows-msvc
#include "..." search starts here:
#include <...> search starts here:
 C:\Dev\LLVM\lib\clang\19\include
 C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\include
 C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\atlmfc\include
 C:\Windows Kits\10\Include\10.0.22621.0\ucrt
 C:\Windows Kits\10\Include\10.0.22621.0\shared
 C:\Windows Kits\10\Include\10.0.22621.0\um
 C:\Windows Kits\10\Include\10.0.22621.0\winrt
 C:\Windows Kits\10\Include\10.0.22621.0\cppwinrt
End of search list.
 "C:\\Dev\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\MSVC\\14.41.34120\\bin\\Hostx64\\x64\\link.exe" -out:test.exe -defaultlib:libcmt -defaultlib:oldnames "-libpath:C:\\Dev\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\MSVC\\14.41.34120\\lib\\x64" "-libpath:C:\\Dev\\Microsoft Visual Studio\\2022\\Community\\VC\\Tools\\MSVC\\14.41.34120\\atlmfc\\lib\\x64" "-libpath:C:\\Windows Kits\\10\\Lib\\10.0.22621.0\\ucrt\\x64" "-libpath:C:\\Windows Kits\\10\\Lib\\10.0.22621.0\\um\\x64" "-libpath:C:\\Dev\\LLVM\\lib\\clang\\19\\lib\\windows" -nologo "C:\\Users\\Aubin\\AppData\\Local\\Temp\\test-91f9da.o"
```
These paths aren't impacted at all by `-nostdinc++`.

Invoking clang with `-nostdinc` work without issue:
```
C:\Dev\Sources\C++ tests>clang++ src/test.cc -nostdinc -o test.exe --verbose
clang version 19.1.3
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Dev\LLVM\bin
 "C:\\Dev\\LLVM\\bin\\clang++.exe" -cc1 -triple x86_64-pc-windows-msvc19.41.34120 -emit-obj -mincremental-linker-compatible -dumpdir test.exe- -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name test.cc -mrelocation-model pic -pic-level 2 -mframe-pointer=none -relaxed-aliasing -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic "-fdebug-compilation-dir=C:\\Dev\\Sources\\C++ tests" -v "-fcoverage-compilation-dir=C:\\Dev\\Sources\\C++ tests" -nostdsysteminc -nobuiltininc -resource-dir "C:\\Dev\\LLVM\\lib\\clang\\19" -fdeprecated-macro -ferror-limit 19 -fmessage-length=175 -fno-use-cxa-atexit -fms-extensions -fms-compatibility -fms-compatibility-version=19.41.34120 -std=c++14 -fskip-odr-check-in-gmf -fdelayed-template-parsing -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -o "C:\\Users\\Aubin\\AppData\\Local\\Temp\\test-4edf30.o" -x c++ src/test.cc
clang -cc1 version 19.1.3 based upon LLVM 19.1.3 default target x86_64-pc-windows-msvc
#include "..." search starts here:
End of search list.
src/test.cc:1:10: fatal error: 'iostream' file not found
    1 | #include <iostream>
      |          ^~~~~~~~~~
1 error generated.
```
But as it removes every search path, I need to manually add them.

When looking from the default system search paths, it should remove the first search path.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzsWU-T26gS_zT40oXKQv578MFjz9ROveSUvOT4CkPLYgeBCpDHvrzP_gok_5t4skl2J2-3Kq5kJEHTNE33r5uGe6-2BnFBxndkvB7wNlTWLe50-9EhDjZWHhaPUPEdAgfBPcJzhQ7hEZ65CRAsSOX5RiOsCLsj7A584EZyJ0GrjePuAMoI3Ur0hK0ivTX6AK1H8AcfsIYKuUTngRsJqy9Hcw-l1do-e1IsyXBNhksyGXb_RNP0LazoZwFSrJT1wSGvSXF_q9sHqWxWnXvTX2UC1FwZwmbxlbutiAKLijvCloQtY9OOsHk_aHrXvQAANE6ZUBI2I4z9hlpb-GydloSxSF_cXc4DDkPrDAzP7dP1i3V1nw_WQahU0ttj0hiZDKmxUX4jOm2TyTDqNO0POmedj_tjep0rs4We8KTmtL7EN21nZH7SF5tn3dR3bQBr4LMyMio-blwcIC16Q9g0gEes48Si4maLwM0hVMpsM_gcZ9fWPsW5eYBQIXjkTlTQ8FB52ESD2HX9QnOzhWcVKtih21iPYNvQtKFbclpVqNDj2Ya-sIHucxU7xqs17sh49cG2TqAn49XRJgP64ElxnyY82qkThD3EnkwIeKFXoDYNynCPQGkvXTdXJ_UOnVfWQD7P8qzoej5yt8VAiiXsZ5P_TEa0EfS50yGt_U70VJVDLqG2EnWkbaxX-67r0fjAtUa5Vi52XS3r3btP78l4tVGmtyTCWE9wojmT9ZTp5WLZcUGEMaBC5ECDU43GV6TN59koz4pRzoZAsVaB2s3vQGtlhMMaTeCaamWe0FFh64YHFWGAyrZupHIn9VGgPUTQ0iECFRq5o9wHusHSOqQbLp7QyDOd1rs66lyVCl1qFtxJuuO6RWp4jR5o9FVaKt01wGkfa4faCh6UNTSpGBolgDZKUI071MCA1qXjNdLGKhPQkWJtrEGgDjXfo6RcK-6jfdKy5qGi6JyxQMuyocKa4LgIpFhbA7Q0ljrbmuhpNNICrYU1PrhWBOs6TlHasjVRtTTE9XlSrBnQkKyFiqaNG0AnI6ChNZgatmjQKRG3mJYSN-026VjpbmEymsf6xuafTf8L64-bvusYCrtDx7f4l_B86TgOfRoQGf6hiWq1uTTR9JrPE9-0N4ZrqvpA8YO80rPHj-9h_F4JZ70tA3xSvuUaPoRWKtt1siFjvUJsXbdGhUP3-WnVPT9aq3uVvf9wbMxHJ4_6W4vFg65L8b0i9tEC_qVCP0Xe83vsefSN2TBjbMLyrO9uhQtvyd9X3KF80xXUb8n9WZm3VZBomvMcpcTGoeABJa25cBH5UmpBtapVgHwecRG9jwCi0WxDRYp1Ph13cNh6pGLPKQ-4VyGSeor7gCZGS999H8OF0iocbjTRPrhGvpdByAdJinWPNPkIaOmfVEOtdFRUKJ6oMnRbl2kNmh9Q0oB1o3lA2nDXQ7rY7ynuBTahF-jqQ1htHZWKbyOuKRHbuJTOq23MCa70_W-Prlf0sj0F22XTrHngPTpZwXXvelg33VvETjrPy7nkmU0635_StKus5DLfSAH7OumADfcooW2sgQiDx2aJJW91gC7AfDUXucyMGcuyLIrT52s-cBc8xHT_nHZdZdKRvrj_Gv3NDKYD6iNKJ4g-osyNQa8DXo92l1D36RLkeoS7hrefN9MJRW9O-cJZk6ee3fSFjyaE_PHhPQD-ifnrPzG4g5YfH39Cp8Ti3kiw5dHmtPIh-2o6_DPi5cn3f7M-7Cej7uP0EpPkU95t23hAOJ8temeNPlEstdqIOrxotFp2OW_M3bTaxHMUKZb_p7Wesqy4PMb-HkJdJizfKuDr0fLdkcMrqcrbca-_T7Xflvue-p6Px_mUtWu7faN4dvOE_jGd47saAHfYlRFU3XARUAIPwLWGzeF2jSO7rKA83igfXI2aDOHZuqfUY9sAyvsW375y8Ktm8Ktm8Ktm8E08k8t0R5jkOMZuWqWDMunrr6og_DrJ_JSTzAhlWQz_aSeZV_PIa7mLZR7_DyOyljxw3ZXZ4ydh03PlfAoRV8DYAGV07vPlQA5kuoI_uKGA9IuEpx8Z3__3-OuI8m7uztGjVWc3I9pdG4B7UAEc1naHHnCH7nBZhu_q6wZRQrBQc9NyrQ_ApYRQYX0Vbq8q-qWzdarpH3emr0NclvjTlUIAX9lWy16GNKZUzodL0mwgF4WcF3M-wEU-LfLZZD4rpoNqkefFdCImU1mMh3ws5rNyJIupyEcTLvLxjA_Ugg3ZKM_zaT4bT_NpVoh8NhRTZLIoZ1giGQ2x5kpnMTBk1m0HKQ1Y5PlkPB4NNN-g9unWizGDz32SELPR9cAtUjTZtFtPRsNoG_7MJqigcXH7KuZ8Z3LjriTmJIPW6UUVQpNuMtgDYQ9bFap2kwlbE_YQZ-kftHH2dxSBsIckmyfsoRd-t2D_CwAA__9Vbnyr">