: undefined symbol: mainCRTStartup
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
```
Happens if you set it like this, or in a toolchain file.
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [March 24, 2022, 7:33am UTC](https://discourse.cmake.org/t/setting-cmake-c-xx-flags-debug-to-in-cmakepresets-json-makes-it-compile-for-x32/5274/2 "2022-03-24T07:33:53Z")
How are you running CMake? From a command line, or from within an IDE? If the former, how did you set up the environment in that shell?
---
### Author:  [@VetleNeumann](https://discourse.cmake.org/u/VetleNeumann)
#### Post date: [March 24, 2022, 7:50am UTC](https://discourse.cmake.org/t/setting-cmake-c-xx-flags-debug-to-in-cmakepresets-json-makes-it-compile-for-x32/5274/3 "2022-03-24T07:50:46Z")
Running CMake from commandline (plain cmd), with Visual Studio’s vcvars64.bat environment on AMD64.
CMake version 3.22.3, Ninja version 1.10.2
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [March 25, 2022, 5:43am UTC](https://discourse.cmake.org/t/setting-cmake-c-xx-flags-debug-to-in-cmakepresets-json-makes-it-compile-for-x32/5274/4 "2022-03-25T05:43:10Z")
It is difficult to know what’s happening in your case. You’ve got a number of very unusual things going on in that CMakePresets.json file, which also mean others can’t reproduce your problem. It seems like you’ve embedded copies of CMake and LLVM binaries in your source tree. That’s very atypical and means you’re at the mercy of whatever those binaries are built/configured to provide. I’ll assume the `cmakeExecutable` can be removed and we can just use a standard CMake installation. The full paths to the clang executables in `CMAKE_CXX_COMPILER` and `CMAKE_C_COMPILER` are more problematic. We don’t know what those compiler binaries will do by default, and the `architecture` value is essentially just an advisory note for IDEs because the `external` strategy is specified. In other words, what you’re seeing is whatever the clang binaries you’ve pointed at will build by default.
---
### Author:  [@VetleNeumann](https://discourse.cmake.org/u/VetleNeumann)
#### Post date: [March 25, 2022, 6:16am UTC](https://discourse.cmake.org/t/setting-cmake-c-xx-flags-debug-to-in-cmakepresets-json-makes-it-compile-for-x32/5274/5 "2022-03-25T06:16:47Z")
Its just my company’s way of providing compilers/tools for a project, and it’s a bit submodules-similar setup where the compiler and CMake are both submodules. That way you can have project specific versions of tools as well. Got any other recommendation for how to provide each developer with these things on a closed network?
But the Clang binaries are Clang’s own 12.0.1 pre-compiled for Windows binaries. If you want I could try this again with these tools installed and removed from the CMakePresets.
And by default it is compiling for x64, it’s just when those values are set to “” it will compile for x32.
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [March 25, 2022, 6:38am UTC](https://discourse.cmake.org/t/setting-cmake-c-xx-flags-debug-to-in-cmakepresets-json-makes-it-compile-for-x32/5274/6 "2022-03-25T06:38:30Z")
There are two things you should confirm:
- If you invoke the clang binaries directly, what sort of target do they build by default? 64-bit or 32-bit? By this I mean invoking them outside of anything to do with CMake, so just running directly at a command line to compile some test file.
- If you don’t explicitly set `CMAKE_CXX_FLAGS_DEBUG` to anything, what does that variable contain by default? About the only way I can see explicitly setting this to an empty string making a difference is if for some reason it contains a setting that changes the target platform (which would be both weird and wrong).