CMake cannot find source file (add_executable)

Question

I have been trying to follow the vendor's tutorial here: CMake-Tutorial, look over the documentation here: Cmake-Documentation, and educate myself as best as possible with sources on YouTube, but I am really struggling with getting the environment set up for working with OpenGL. Having tinkered with the Glitter boilerplate and the tutorials on open.gl and learnopengl.com, I've decided that understanding the build process is too important not to investigate.

In my investigation, I have come across the CMake error "cannot find source file" which is shown below in more detail. The problem seems to be arising from "add_executable".

A similar question was asked here: CMake - Cannot find file. The solution involved ensuring that the ${PROJECT_SOURCE_DIR} was set properly for each variable, which I believe I have done.

My file structure:

+ infuriating_project
    + bin // post compile results
    + src // my humble code
    + deps // external code
        +glew
            + include
            + src
        +glfw
            + include
            + src
        +glm
        +soil
            + lib
            + src

My CMakeLists.txt:

cmake_minimum_required (VERSION 3.0)


# Version Information ---------------------------------------------------------
project (openGL-practice)
SET (VERSION_MAJOR 1)
SET (VERSION_MINOR 0)
SET (VERSION_FEATURE 0)
SET (VERSION_PATCH 0)
SET (VERSION "${VERSION_MAJOR}.${VERSION_MINOR}")
SET (VERSION "${VERSION}.${VERSION_FEATURE}.${VERSION_PATCH}")
MESSAGE ("Version: ${VERSION}")

# Configure Source & Binary Directories ---------------------------------------
SET (PROJECT_ROOT "${PROJECT_SOURCE_DIR}")
SET (PROJECT_SOURCE_DIR "${PROJECT_SOURCE_DIR}/src")
SET (PROJECT_BINARY_DIR "${PROJECT_BINARY_DIR}/bin")
MESSAGE ("Source path: ${PROJECT_SOURCE_DIR}")
MESSAGE ("Binary path: ${PROJECT_BINARY_DIR}")

# Configure Depenency Directories ---------------------------------------------
SET (PROJECT_DEPS "${PROJECT_ROOT}/deps")
SET (glew_inc "${PROJECT_DEPS}/glew/include/GL/")
SET (glew_src "${PROJECT_DEPS}/glew/src/")
SET (glfw_inc "${PROJECT_DEPS}/glfw/include/GLFW/")
SET (glfw_src "${PROJECT_DEPS}/glfw/src/")
SET (glm "${PROJECT_DEPS}/glm/glm/")
SET (soil_lib "${PROJECT_DEPS}/lib/")
SET (soil_src "${PROJECT_DEPS}/src/")

# Include directories ---------------------------------------------------------
include_directories("
    ${PROJECT_SOURCE_DIR}
    ${PROJECT_BINARY_DIR}
    ${glew_inc}
    ${glew_src}
    ${glfw_inc}
    ${glfw_src}
    ${glm}
    ${soil_lib}
    ${soil_src}
    ${PROJECT_ROOT}
    ")

# Add executable --------------------------------------------------------------
add_executable(main main.cpp)

The following error is provided:

CMake Error at CMakeLists.txt:46 (add_executable):
  Cannot find source file:

    main.cpp

  Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp
  .hxx .in .txx


CMake Error: CMake can not determine linker language for target: main
CMake Error: Cannot determine link language for target "main".

Any and all help would be very much appreciated.

Answer 1

In add_executable() call relative paths are always interpreted relative to variables CMAKE_CURRENT_SOURCE_DIR or CMAKE_CURRENT_BINARY_DIR.

If you have source files in subdirectories of these dirs, you should explicitely specify these subdirectories:

add_executable(main src/main.cpp)

---

Also, variables like PROJECT_SOURCE_DIR should be treated as readonly: while changing them isn't detected by CMake as an error, it breaks some things.

Answer 2

There are some points I'd like to mention.

1. include_directories helps for finding header files. Source files must always have a complete relative path.

   Assuming that your main.cpp is within src, the correct syntax is

   add_executable(main ${PROJECT_SOURCE_DIR}/main.cpp)
   

2. Including ${PROJECT_BINARY_DIR} does not make sense.

3. Overwriting CMake default variables like ${PROJECT_SOURCE_DIR} is no good practice. In future you will always remember that you have done such a thing and for another programmer it is quite unexpected.

Hope it helps.