# Unexpected behavior when using target\_sources

**URL:** <https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926>\
**Category:** Code\
**Created:** [August 6, 2025, 4:36pm UTC](https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926 "2025-08-06T16:36:46Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Idono](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/i/ea666f/32.png) [@Idono](https://discourse.cmake.org/u/Idono)\
**Post date:** [August 6, 2025, 4:36pm UTC](https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926/1 "2025-08-06T16:36:46Z")

</div>

Hi.

I’m relatively new to cmake and learning it mostly doing small projects. I’ve got some questions related to target\_sources. My understanding of it is that if i omit source files in add\_library i should be able to add sources files with differing access with target\_sources. But i’m encountering an issue where one of my external library headers that are included with find\_package can not be found when using target\_sources to add source file but works perfectly fine when adding source files in add\_library.

The cmake configuration is fairly easy for my library as seen below.

```cmake
# Public source files
set(PUBLIC_SOURCE_FILES)
list(APPEND PUBLIC_SOURCE_FILES Core.cpp)

list(TRANSFORM PUBLIC_SOURCE_FILES PREPEND "lib/")

# Private source files
set(PRIVATE_SOURCE_FILES)
list(APPEND PRIVATE_SOURCE_FILES Window.cpp)

list(TRANSFORM PRIVATE_SOURCE_FILES PREPEND "lib/")

add_library(Core)

target_link_libraries(Core PRIVATE glfw)
target_link_libraries(Core PRIVATE glbinding::glbinding glbinding::glbinding-aux)
target_link_libraries(Core PRIVATE glm::glm)

target_sources(Core PRIVATE ${PRIVATE_SOURCE_FILES})
target_sources(Core PUBLIC ${PUBLIC_SOURCE_FILES})

target_include_directories(Core PRIVATE lib)
target_include_directories(Core PUBLIC includes)

```

There are two specific source files with headers. The window source file and header are both meant to be private in the library. They are both including the GLFW external library. The core source file includes the window header file and the header file has public definitions with no includes.

When the window header is included in the core source file the GLFW headers can not be found in the Window header and source file. But the window header is removed from the core source file they can be found again. The happens if the GLFW headers are included in the core source files.

I’ve tried moving things around but nothing except adding source files with add\_library seems to work.

Is there some obscure functionality that i’ve missed regarding adding source files to targets?

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<div class="post-metadata">

**Author:** ![vito.gamberini](https://discourse.cmake.org/user_avatar/discourse.cmake.org/vito.gamberini/32/4376_2.png) [@vito.gamberini](https://discourse.cmake.org/u/vito.gamberini)\
**Post date:** [August 6, 2025, 4:55pm UTC](https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926/2 "2025-08-06T16:55:19Z")

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`target_sources()` has no impact on `#include` resolution when used in the demonstrated manner. (It has a separate keyword, `FILE_SET`, for handling headers but you’re using `target_include_directories` here)

You will need to post the complete project (preferably a Github or Gist link), or a minimal reproducible example, there is not enough information here to answer your question.

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<div class="post-metadata">

**Author:** ![Idono](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/i/ea666f/32.png) [@Idono](https://discourse.cmake.org/u/Idono)\
**Post date:** [August 6, 2025, 5:53pm UTC](https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926/3 "2025-08-06T17:53:22Z")

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Here’s a git repo with the reproduced problem. The main issue lies in the Core.cpp source file

> **[GitHub - Idono87/cmake\_target\_sources\_example](https://github.com/Idono87/cmake_target_sources_example)**
>
> Contribute to Idono87/cmake\_target\_sources\_example development by creating an account on GitHub.

Also as a side note. I’m using clang 20.1.8 and ninja as my compiler and generator on a windows machine.

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<div class="post-metadata">

**Author:** ![vito.gamberini](https://discourse.cmake.org/user_avatar/discourse.cmake.org/vito.gamberini/32/4376_2.png) [@vito.gamberini](https://discourse.cmake.org/u/vito.gamberini)\
**Post date:** [August 6, 2025, 6:09pm UTC](https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926/4 "2025-08-06T18:09:13Z")

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There’s really no such thing as a “public” implementation file. The problem is you’re putting `Core.cpp` in your `PUBLIC` source file list. The `Enigma` target tries to build this file, which it should not.

Since you marked `glfw` as a `PRIVATE` dependency of `Core`, the include directories it provides are not propagated to `Enigma`. Thus, when `Enigma` tries to build `Core.cpp`, it fails.

The answer here is to not have any `PUBLIC` implementation files. Such things have very limited and specialized use cases, and this is not such a use case.

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<div class="post-metadata">

**Author:** ![Idono](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/i/ea666f/32.png) [@Idono](https://discourse.cmake.org/u/Idono)\
**Post date:** [August 6, 2025, 6:25pm UTC](https://discourse.cmake.org/t/unexpected-behavior-when-using-target-sources/14926/5 "2025-08-06T18:25:11Z")

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Alright that makes a whole lot of sense. Thanks for the help.