# Is it normal to get alot of warnings when compling under windows?

**URL:** https://discourse.paraview.org/t/is-it-normal-to-get-alot-of-warnings-when-compling-under-windows/13742
**Category:** Development
**Created:** [January 19, 2024, 6:01pm UTC](https://discourse.paraview.org/t/is-it-normal-to-get-alot-of-warnings-when-compling-under-windows/13742 "2024-01-19T18:01:19Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![uporersith](https://discourse.paraview.org/user_avatar/discourse.paraview.org/uporersith/32/10957_2.png) [@uporersith](https://discourse.paraview.org/u/uporersith)
#### Post date: [January 19, 2024, 6:01pm UTC](https://discourse.paraview.org/t/is-it-normal-to-get-alot-of-warnings-when-compling-under-windows/13742/1 "2024-01-19T18:01:19Z")

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I’m following the directions from here: [https://gitlab.kitware.com/paraview/paraview/-/blob/master/Documentation/dev/build.md#windows](https://gitlab.kitware.com/paraview/paraview/-/blob/master/Documentation/dev/build.md#windows)  
(I’m building v5.12.0-RC2)

When i get to the ninja step, I get alot of these warnings:

```auto
[185/22066] Building CXX object 
VTK\Common\Core\CMakeFiles...CompositeImplicitBackendInstantiate_unsigned_short.cxx.obj
C:\pv\pv\VTK\Common\Core\vtkCompositeImplicitBackend.h(80): warning C4251: 'vtkCompositeImplicitBackend<ValueType>::Internal': class 'std::unique_ptr<vtkCompositeImplicitBackend<ValueType>::Internals,std::default_delete<vtkCompositeImplicitBackend<ValueType>::Internals>>' needs to have dll-interface to be used by clients of class 'vtkCompositeImplicitBackend<ValueType>'

```

Is that normal?

Should I expect the ninja build process to go through without any warnings?

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<div class="post-metadata">

### Author: ![ben.boeckel](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.paraview.org/u/ben.boeckel)
#### Post date: [January 19, 2024, 8:28pm UTC](https://discourse.paraview.org/t/is-it-normal-to-get-alot-of-warnings-when-compling-under-windows/13742/2 "2024-01-19T20:28:16Z")

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C4251 is a useless warning for projects with more than a single DLL that communicate over a C++ API (in particular, it is saying that you cannot inherit from a class that is not in your own DLL). Just ignore it with `-wd4251`.