Add of cmake_ dependencies

brief introduction

add_dependencies(<target> [<target-dependency>]...)

• Official documents explain this as ： Add dependencies between top-level goals . Make top layer target Rely on other top-level goals , To make sure they're in target Before building . The top goal is made up of add_executable(),add_library() or add_custom_target() Created by one of the commands .

example

Directory structure

├── CMakeLists.txt
├── lib
│ ├── CMakeLists.txt
│ ├── mymath.cpp
│ └── mymath.h
└── src
├── CMakeLists.txt
└── main.cpp

Outermost layer cmake

# Appoint cmake Minimum version 
cmake_minimum_required(VERSION 3.14)

# Specify project name 
project(demo)

# Add subdirectories 
add_subdirectory(${PROJECT_SOURCE_DIR}/src)
add_subdirectory(${PROJECT_SOURCE_DIR}/lib)

lib Under the table of contents cmake

# Appoint cmake Minimum version 
cmake_minimum_required(VERSION 3.14)

// Specify the library file generation directory 
set(LIBRARY_OUTPUT_PATH ${PROJECT_BINARY_DIR}/bin)

// Generate library files 
add_library(myMath SHARED ${PROJECT_SOURCE_DIR}/lib/mymath.cpp)

src Under the table of contents cmake

# Appoint cmake Minimum version 
cmake_minimum_required(VERSION 3.14)

# Specify the location of the header file 
include_directories(${PROJECT_SOURCE_DIR}/lib)

# Set the executable file generation directory 
set(EXECUTABLE_OUTPUT_PATH ${PROJECT_BINARY_DIR}/bin)

# Generate executable files 
add_executable(res ${PROJECT_SOURCE_DIR}/src/main.cpp)

# Link dynamic library 
target_link_libraries(res ${PROJECT_BINARY_DIR}/bin/libmyMath.so)

test

• We compile the code directly

[[email protected] build]# make
Scanning dependencies of target res
[ 25%] Building CXX object src/CMakeFiles/res.dir/main.cpp.o
make[2]: *** No rule to make target 'bin/libmyMath.so', needed by 'bin/res'.  Stop.
make[1]: *** [CMakeFiles/Makefile2:91: src/CMakeFiles/res.dir/all] Error 2
make: *** [Makefile:84: all] Error 2
[[email protected] build]# 

• You can see that there will be errors , Because when we add subdirectories on the outermost layer , To add src subdirectories , That is to say, we are generating executable files res when , When linking library files , The library file has not been generated . Of course, you can adjust the order of adding subdirectories , Sir, the library file , Regenerate into executable . But in real development , When linking library files , There are still many scenes in which the library file has not been generated .
• It can be used at this time add_dependencies command . modify src In the catalog cmake

# Appoint cmake Minimum version 
cmake_minimum_required(VERSION 3.14)

# Specify the location of the header file 
include_directories(${PROJECT_SOURCE_DIR}/lib)

# Set the executable file generation directory 
set(EXECUTABLE_OUTPUT_PATH ${PROJECT_BINARY_DIR}/bin)

# Generate executable files 
add_executable(res ${PROJECT_SOURCE_DIR}/src/main.cpp)

# Designated dependency 
add_dependencies(res myMath)

# Link dynamic library 
target_link_libraries(res ${PROJECT_BINARY_DIR}/bin/libmyMath.so)

• add to add_dependencies(res myMath), It means to tell the compiler , I know generate res Program to link myMath This library file , But now I don't have this library file , Your husband Cheng res, I then put the library file myMath Generate it for you .