# Important Update: Standard iostream availability from VTK

**URL:** https://discourse.vtk.org/t/important-update-standard-iostream-availability-from-vtk/16171
**Category:** Development
**Tags:** code
**Created:** [December 3, 2025, 3:07pm UTC](https://discourse.vtk.org/t/important-update-standard-iostream-availability-from-vtk/16171 "2025-12-03T15:07:57Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![sankhesh](https://discourse.vtk.org/user_avatar/discourse.vtk.org/sankhesh/32/73_2.png) [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [December 3, 2025, 3:07pm UTC](https://discourse.vtk.org/t/important-update-standard-iostream-availability-from-vtk/16171/1 "2025-12-03T15:07:57Z")

</div>

Please note a significant change in VTK.

In the changeset from Merge Request [!11993](https://gitlab.kitware.com/vtk/vtk/-/merge_requests/11993), the inclusion of `<iostream>` has been removed from a core header. This change previously caused global constructors to be triggered in every downstream translation unit.

As a result, applications that link to VTK can no longer assume that objects such as `cin`, `cout`, and `cerr` are automatically available. To ensure compatibility with this update, applications must now explicitly `#include <iostream>` and use the `std` namespace when referring to standard I/O streams, such as `std::cin`, `std::cout`, and `std::cerr`.