cmake with vcpkg on macOS cannot find header files - c++

Question

I installed vcpkg on macOS and I'm trying to build a simple library that depends on fmt, which I installed with vcpkg.
mylib.h
float add(float a, float b);
mylib.cpp
#include "mylib.h"
#include <iostream>
#include <fmt/core.h>
float add(float a, float b)
{
fmt::print("Hello MYLIB, world!\n");
return (a + b);
}
CMakeLists.txt contents:
cmake_minimum_required(VERSION 3.19.1)
project(MYLIB)
find_package(fmt REQUIRED)
add_library(mylib mylib.cpp)
Then
user#users-MacBook-Pro build % cmake -B . -DCMAKE_TOOLCHAIN_FILE=~/vcpkg/scripts/buildsystems/vcpkg.cmake -S ..
-- The C compiler identification is AppleClang 12.0.0.12000032
-- The CXX compiler identification is AppleClang 12.0.0.12000032
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/user/mylib/build
user#users-MacBook-Pro build % make
Scanning dependencies of target mylib
[ 50%] Building CXX object CMakeFiles/mylib.dir/mylib.cpp.o
/Users/user/mylib/mylib.cpp:5:10: fatal error: 'fmt/core.h' file not found
#include <fmt/core.h>
^~~~~~~~~~~~
1 error generated.
make[2]: *** [CMakeFiles/mylib.dir/mylib.cpp.o] Error 1
make[1]: *** [CMakeFiles/mylib.dir/all] Error 2
make: *** [all] Error 2
What am I missing?
I tried the same on Windows and it works fine. On Windows though we run vcpkg integrate install which does not exist on macOS. Is this related to the problem?

Answer 1

Looks like it's necessary to
include_directories(~/vcpkg/installed/x64-osx/include)

Answer 2

You are using the variable CMAKE_TOOLCHAIN_FILE incorrectly. set(CMAKE_TOOLCHAIN_FILE ... in CMakeLists.txt has no effect. The variable should be set on the command line, see the manuals CMAKE_TOOLCHAIN_FILE, Using vcpkg with CMake
cmake .. -DCMAKE_TOOLCHAIN_FILE=~/vcpkg/scripts/buildsystems/vcpkg.cmake
The file CMakeLists.txt is also wrong, find_package(fmt REQUIRED) is missing, that should download and install fmt by invoking vcpkg install fmt under the hood.
After all you should link your project with the lib
target_link_libraries(MYLIB PRIVATE fmt::fmt)