# How to distinguish WIndows Architecture
**URL:** https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104
**Category:** Usage
**Created:** [February 23, 2022, 6:09pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104 "2022-02-23T18:09:02Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@fabiop](https://discourse.cmake.org/u/fabiop)
#### Post date: [February 23, 2022, 6:09pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104/1 "2022-02-23T18:09:02Z")
Hi all,
Is there any CMake variable for distinguish, on Windows, if we are building for 32 bits Architecture or 64 bits Architecture?
Thanks in advance for any help
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [February 23, 2022, 6:15pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104/2 "2022-02-23T18:15:13Z")
Have a look at [CMAKE\_SIZEOF\_VOID\_P](https://cmake.org/cmake/help/latest/variable/CMAKE_SIZEOF_VOID_P.html) variable.
---
### Author:  [@buildSystemPerson](https://discourse.cmake.org/u/buildSystemPerson)
#### Post date: [February 24, 2022, 9:35pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104/3 "2022-02-24T21:35:40Z")
```auto
if (CMAKE_SIZE_OF_VOID_P EQUAL 4)
message(STATUS "32 bit")
endif()
if (CMAKE_SIZE_OF_VOID_P EQUAL 8)
message(STATUS "64 bit")
endif()
```
---
### Author:  [@fabiop](https://discourse.cmake.org/u/fabiop)
#### Post date: [March 2, 2022, 1:46pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104/4 "2022-03-02T13:46:44Z")
Ok, but if I am on a 64 bits Host machine, but I build with -A 32 bits flag, the sizeof of the word is 4 bytes or 8 bytes? I think it will be the latter…
---
### Author:  [@marc.chevrier](https://discourse.cmake.org/u/marc.chevrier)
#### Post date: [March 2, 2022, 1:59pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104/5 "2022-03-02T13:59:54Z")
The variable `CMAKE_SIZE_OF_VOID_P` describes your build environment, not the host on which you are running… So it will be 4 bytes.
---
### Author:  [@buildSystemPerson](https://discourse.cmake.org/u/buildSystemPerson)
#### Post date: [March 2, 2022, 3:20pm UTC](https://discourse.cmake.org/t/how-to-distinguish-windows-architecture/5104/6 "2022-03-02T15:20:02Z")
On Windows you basically have 4 different compilers (for x86/AMD64):
```auto
# C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Visual Studio 2022\Visual Studio Tools\VC
# Host 64 -> Target 64
x64 Native Tools Command Prompt for VS 2022
# Host 64 -> Target 32
x64_x86 Cross Tools Command Prompt for VS 2022
# Host 32 -> Target 64
x86_x64 Cross Tools Command Prompt for VS 2022
# Host 32 -> Target 32
x86 Native Tools Command Prompt for VS 2022
```
I never recommend using the last 2 for larger applications since big projects tend to use more than 4 GB of RAM.
Anyway CMake lets you pick both your host tools and your target platform. They are different things.
From the CMake docs:
```auto
The CMAKE_GENERATOR_PLATFORM variable may be set, perhaps via the cmake(1) -A option, to specify a target platform name (architecture). For example:
- cmake -G "Visual Studio 17 2022" -A Win32
- cmake -G "Visual Studio 17 2022" -A x64
- cmake -G "Visual Studio 17 2022" -A ARM
- cmake -G "Visual Studio 17 2022" -A ARM64
```
If you want to choose different host tools here are the [docs](https://cmake.org/cmake/help/latest/generator/Visual%20Studio%2017%202022.html#toolset-selection). However, VS2019 and newer use 64-bit tools by default.