Adding standard libraries to use for every link target

Usage
1

I am attempting to build for Windows XP using VS 2015 on Windows 10. Several parts of the code require us to link against Microsofts psapi.lib in this “cross compilation” case. I have attempted to

set (CMAKE_C_STANDARD_LIBRARIES “${CMAKE_C_STANDARD_LIBRARIES} psapi.lib”)

in a toolchain file but this does not work. Using

set (CMAKE_C_STANDARD_LIBRARIES_INIT “${CMAKE_C_STANDARD_LIBRARIES_INIT} psapi.lib”)

also does not have the desired effect. In both cases psapi.lib is not used on linking.
Have I misunderstood the documentation ( CMAKE__STANDARD_LIBRARIES — CMake 3.19.2 Documentation)?

2

@brad.king

3

See CMake Issue 20575.

The best solution for your use case IMO is to just use target_link_libraries to explicitly link psapi.lib to whatever target contains the code needing it. Another alternative is the link_libraries command.

4

We are trying to keep platform specific aspects out of the code and out of the build specifications, e.g. cmake files as much as possible. To a large degree cmake supports this approach for us. Thanks to the cmake team for this.
Phrasing a dependency to a library that is only required on windows when “cross compiling” from Windows 10 to Windows XP in inner parts of the build specification did not exite me, so I looked for alternatives. The toolchain file seemed like a good idea for this purpose. Why I did not use link_libraries? It did not even occur to me that this would be allowed in a toolchain file. Also I found a reference to CMAKE_C_STANDARD_LIBRARIES and thought that it was intended for such a purpose.

5

link_libraries shouldn’t be called from a toolchain file. It might work, but it isn’t really meant for that. My suggestion was assuming you’d modify the project code.

You should be able to set CMAKE_C_STANDARD_LIBRARIES as a cache entry in the toolchain file with the complete list of libraries needed for that platform, including all the ones CMake normally adds by default.

6

One way that you can do this is to create your own add_library(project_settings INTERFACE) target that all of your targets link to. You can add psapi.lib here as well as any flags you’d like all targets to use as well.

7

What I did was to add psapi.dll to the existing content of CMAKE_C_STANDARD_LIBRARIES (see code in first post). This did not work. I also used CMAKE_C_STANDARD_LIBRARIES_INIT in this fashion without success. I think what happens is:

  1. both the variables are empty during processing of the toolchain file.
  2. the contents of the variables are overwritten by some part of cmake later. Maybe the code in ./share/cmake-3.17/Modules/Platform/Windows-MSVC.cmake is the “culprit”.

In my toolchain file I also use statements such as

set (CMAKE_C_FLAGS_INIT “${CMAKE_C_FLAGS_INIT} /D_USING_V110_SDK71_”)

which work as expected.

8

Being able to set CMAKE_C_FLAGS_INIT in a toolchain file such that CMake’s builtin modules only append to it was added by commit a66004bee0 in CMake 3.7. A similar change could be made for CMAKE_C_STANDARD_LIBRARIES.

Lacking that, you should be able to use

set(CMAKE_C_STANDARD_LIBRARIES "kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib psapi.lib" CACHE STRING "C std libs")

in your toolchain file.

9

Or I

set (CMAKE_EXE_LINKER_FLAGS_INIT “${CMAKE_EXE_LINKER_FLAGS_INIT} psapi.lib”)
set (CMAKE_SHARED_LINKER_FLAGS_INIT “${CMAKE_SHARED_LINKER_FLAGS_INIT} psapi.lib”)

I do not really like either solution. On the other hand I do not like to compile for 32 Bit XP in 2020 either!

10

Sure. For reference, being able to set CMAKE_EXE_LINKER_FLAGS_INIT and friends in a toolchain file was added by commit 8a98cf6432 in CMake 3.7. I suggest using

string(APPEND CMAKE_EXE_LINKER_FLAGS_INIT  " psapi.lib")