cmake Visual Studio nested shared library subproject

Question

Overview

• I want to compile a project CalcMod using a shared library XMMathLib.
• Both should be loaded as projects in Visual Studio (ie in the Solution Explorer, there should be a tree for CalcMod, and a tree for XMMathLib). Hence nesting XMMathLib within CalcMod (and adding it with add_subdirectory()) seems to be the apropriate solution.
• Also, eventually, we want to export XMMathLib as a (shared) dll library, hence we call add_library(XMMathLib SHARED […]).
• However, this triggers a cannot open file 'XMMathLib\Debug\XMMathLib.lib' error at the end of compilation.
  Indeed, the folder build\XMMathLib\Debug\ contains XMMathLib.dll, XMMathLib.ilk and XMMathLib.pdb, which is consistent with me asking to generate a shared library for XMMathLib. But then, why does CalcMod look for static library file XMMathLib.lib?!

Details

Here is how the project is organised:

 |- build
 |- src
     |- CalcMod
     |   |- src
     |       |- main.cpp
     |- XMMathLib
     |   |- src
     |   |   |- Demo.cpp
     |   |   |- Demo.h
     |   |- CMakeLists.txt
     |- CMakeLists.txt

And here is the content of each file:

src/CMakeLists.txt

cmake_minimum_required(VERSION 3.22 FATAL_ERROR)
project(CalcMod CXX)
set(CMAKE_CXX_STANDARD 14)
add_subdirectory(XMMathLib)

file(GLOB_RECURSE SOURCES_CALCMOD "CalcMod/src/*.cpp")
source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR} FILES ${SOURCES_CALCMOD})
add_executable(
    CalcMod
    ${SOURCES_CALCMOD}
    )
target_link_libraries(
    CalcMod
    XMMathLib
    )
target_include_directories(CalcMod PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

src/XMMathLib/CMakeLists.txt

cmake_minimum_required(VERSION 3.22 FATAL_ERROR)
project(XMMathLib CXX)
file(GLOB_RECURSE SOURCES "src/*.cpp")
add_library(XMMathLib SHARED ${SOURCES})
target_link_libraries(
    XMMathLib
    )

src/CalcMod/src/main.cpp

#include <iostream>
#include "XMMathLib/src/Demo.h"

int main()
{
    RunDemo();
}

src/XMMathLib/src/Demo.cpp

#include <iostream>

void RunDemo()
{
    std::cout << "hello" << std::endl;
}

src/XMMathLib/src/Demo.h

#pragma once
void __declspec(dllexport) RunDemo();

cmake parameters:

• Visual Studio 2017
• Platform: Win32
• Windows SDK 10.0.19041.0

Answer 1

Many thanks to all of you for helping me out, especially drescherjm !

Below is the fixed variant of my originally broken code:

 |- build
 |- src
     |- CalcMod
     |   |- src
     |       |- main.cpp
     |- XMMathLib
     |   |- src
     |   |   |- Demo.cpp
     |   |   |- Demo.h
     |   |   |- DllExport.h
     |   |- CMakeLists.txt
     |- CMakeLists.txt

And here is the content of each file:

src/CMakeLists.txt

cmake_minimum_required(VERSION 3.22 FATAL_ERROR)
project(CalcMod CXX)
set(CMAKE_CXX_STANDARD 14)

add_subdirectory(XMMathLib)  # Call XMMathLib's CMakeLists.txt

file(GLOB_RECURSE SOURCES_CALCMOD "CalcMod/src/*.cpp" "CalcMod/src/*.h" "CalcMod/src/*.hpp")  # Files to compile. Also all the files that will appear in VS's Solution Explorer (that's why we include the headers here).
source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR} FILES ${SOURCES_CALCMOD})  # So that source files appear in Solution Explorer as a tree reproducing their actual location
add_executable(  # Ask VS to generate a CalcMod.exe executable as output
    CalcMod
    ${SOURCES_CALCMOD}
    )
target_link_libraries(  # Tell VS's linker to link with XMMathLib.dll
    CalcMod
    PUBLIC XMMathLib
    # PRIVATE: CalcMod uses XMMathLib and noone else
    # INTERFACE: CalcMod does not use XMMathLib but makes it available to others
    # PUBLIC: CalcMod uses XMMathLib *and* makes it available to others.
    )
target_include_directories(CalcMod PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})  # Add include directories (ie gcc's -I option)

# We want to copy XMMathLib.dll at the same location than CalcMod.exe, otherwise it won't run because it won't find it.

# Option #1: Copy the dlls of all the dependent libraries (only XMMathLib in this case) to where CalcMod.exe is
# Pros: Only copy the useful files (ie the *.dll) leaving behind eg the *.ilk and *.exp
#       No need to specify explicitly all dependent libraries
# Cons: Does not copy the *.pdb which is required by the debuger (contains the debug symbols)
# Copy eg XMMathLib.dll from `build\XMMathLib\Debug` to `build\Debug
#add_custom_command(TARGET CalcMod POST_BUILD
#  COMMAND ${CMAKE_COMMAND} -E copy $<TARGET_RUNTIME_DLLS:CalcMod> $<TARGET_FILE_DIR:CalcMod>
#  COMMAND_EXPAND_LISTS
#  )

# Option #2: Copy all the output files (*.dll, *.pdb, *.ilk, *.exp) generated by XMMathLib where CalcMod.exe
# Pros: Copies *.pdb which is required by the debbuger (contains the debug symbols)
# Cons: Have to manually list all the dependent libraries explicitly (only one in this case: XMMathLib)
#       Also copies *.ilk and *.exp which are used for building/linking but are just bloat after that.
add_custom_command(TARGET CalcMod POST_BUILD
  COMMAND ${CMAKE_COMMAND} -E copy_directory $<TARGET_FILE_DIR:XMMathLib> $<TARGET_FILE_DIR:CalcMod>
  COMMAND_EXPAND_LISTS
  )

src/XMMathLib/CMakeLists.txt

cmake_minimum_required(VERSION 3.22 FATAL_ERROR)

project(XMMathLib CXX)

file(GLOB_RECURSE SOURCES "src/*.cpp" "src/*.hpp" "src/*.h")  # List sources to use in build

add_compile_definitions(XMMATHLIB_EXPORTS)  # When defined, export.h will use __declspec(dllexport)

add_library(XMMathLib SHARED ${SOURCES})  # Ask VS to build XMMathLib.dll

target_link_libraries(  # Tell VS's linker to link with libraries. Actually unnecessary here (no library linked)
    XMMathLib
    )

src/CalcMod/src/main.cpp

#include <iostream>

#include "XMMathLib/src/Demo.h"

int main()
{
    RunDemo();
}

src/XMMathLib/src/Demo.cpp

#include <iostream>
#include "Demo.h"  // We need to include Demo.h, otherwise VS won't see __declspec(dllexport) for RunDemo() and won't export the function

void RunDemo()
{
    std::cout << "hello" << std::endl;
}

src/XMMathLib/src/Demo.h

#include "DllExport.h"

void XMMATHLIB_DLLEXPORT RunDemo();

src/XMMathLib/src/DllExport.h

#pragma once

// Tells VS whether to specify the functions and classes marked with XMMATHLIB_DLLEXPORT
// as to be exported in the *.lib that accompanies the *.dll or not.
// If no class or function is marked with __declspec(dllexport), then XMMathLib.lib won't be generated.

#if XMMATHLIB_EXPORTS
    #define XMMATHLIB_DLLEXPORT __declspec(dllexport)
#else
    #define XMMATHLIB_DLLEXPORT __declspec(dllimport)
#endif

cmake parameters:

• Visual Studio 2017
• Platform: Win32
• Windows SDK 10.0.19041.0