cmake import exist SimpleAmqp library

Question

Now my CMakeList.txt looking like this.

cmake_minimum_required(VERSION 3.6)
project(RabbitMQClient)

set(CMAKE_CXX_STANDARD 11)

set(SOURCE_FILES main.cpp)
include_directories(src)
include_directories(dependentFile)
add_executable(RabbitMQClient ${SOURCE_FILES})
find_library(SimpleAmqpClient SimpleAmqpClient.2.lib PATHS ./SimpleAmqpClientLib/SimpleAmqpClient.2.lib)
set(IMPORTED_IMPLIB ./SimpleAmqpClientLib)
target_link_libraries(RabbitMQClient PUBLIC SimpleAmqpClient)

when Linking the RabbitMQClient it complains.

cannot find -lSimpleAmqpClient

I want to use the SimpleAmqpClient library in the project,however not quite familiar with cmake not sure the find_library,IMPORTED_IMPLIB,PUBLIC in target_link_libraries was correctly used.Any help would be appreciate.

Answer 1

You have messed up with variables, targets and properties.

Proper usage of IMPORTED libraries for linking would be:

# This command sets *variable* SimpleAmqpClient_LIBRARY
find_library(SimpleAmqpClient_LIBRARY SimpleAmqpClient.2.lib
    PATHS ${CMAKE_SOURCE_DIR}/SimpleAmqpClientLib # Specify a *directory*, not a library *file*
)
# Next, create an IMPORTED *target*
add_library(SimpleAmqpClient SHARED IMPORTED)
# And set IMPORTED_LIB *property* for this target
set_target_properties(SimpleAmqpClient PROPERTIES IMPORTED_LIB ${SimpleAmqpClient_LIBRARY})
# Then use library *target* for linking with
target_link_libraries(RabbitMQClient PUBLIC SimpleAmqpClient)

However, there some simplifications which could be done:

1. Normally, find_library is used when you don't know complete path to the library file. E.g., its directory may be different on different machines, or its prefix/extension may be different on different plaforms.

   If you know complete path to the library, just use this path directly (e.g., assign it to the variable).

2. Normally, property IMPORTED_LOCATION is used for specify library to link with. Property IMPORTED_LIB is specific for Windows .dlls, when linking requires not a library file (.dll), but some other one (.lib).

   However, CMake perfectly understands .lib file in IMPORTED_LOCATION property even for Windows .dlls, so your code need not distinguish SHARED Windows libraries from others: just use IMPORTED_LOCATION property in all cases.

Simplified version of the code:

# Create an IMPORTED library *target*
add_library(SimpleAmqpClient IMPORTED)
# Set IMPORTED_LOCATION *property* for this target
set_target_properties(SimpleAmqpClient PROPERTIES
    IMPORTED_LOCATION ${CMAKE_SOURCE_DIR}/SimpleAmqpClientLib/SimpleAmqpClient.2.lib)
# Then use library *target* for linking with
target_link_libraries(RabbitMQClient PUBLIC SimpleAmqpClient)