add_library使用 $＜TARGET_OBJECTS:name＞

一、背景

前面介绍了add_library的两种格式，今天分享一个实例:

Cmake分别生成静态链接库，OBJ链接库，并使用$<TARGET_OBJECTS:name>引用obj文件

二、实例

文件目录如下

CMakeList.txt文件

# set minimum cmake version
cmake_minimum_required(VERSION 3.5 FATAL_ERROR)

# project name and language
project(recipe-03 LANGUAGES CXX)

# generate an object library from sources
add_library(message-objs
  OBJECT
    Message.hpp
    Message.cpp
  )

# 开启(PIC) 编译动态库
set_target_properties(message-objs
  PROPERTIES
    POSITION_INDEPENDENT_CODE True
  )

add_library(message-shared
  SHARED
    $<TARGET_OBJECTS:message-objs>
  )

set_target_properties(message-shared
  PROPERTIES
    OUTPUT_NAME "message"
  )

add_library(message-static
  STATIC
    $<TARGET_OBJECTS:message-objs>
  )

set_target_properties(message-static
  PROPERTIES
    OUTPUT_NAME "message"
  )

add_executable(hello-world hello-world.cpp)

target_link_libraries(hello-world message-static)

Message.hpp文件

#pragma once

#include <iosfwd>
#include <string>

class Message {
public:
  Message(const std::string &m) : message_(m) {}

  friend std::ostream &operator<<(std::ostream &os, Message &obj) {
    return obj.printObject(os);
  }

private:
  std::string message_;
  std::ostream &printObject(std::ostream &os);
};

Message.cpp文件

#include "Message.hpp"

#include <iostream>
#include <string>

std::ostream &Message::printObject(std::ostream &os) {
  os << "This is my very nice message: " << std::endl;
  os << message_;

  return os;
}

hello-word.cpp

#include "Message.hpp"

#include <cstdlib>
#include <iostream>

int main() {
  Message say_hello("Hello, CMake World!");

  std::cout << say_hello << std::endl;

  Message say_goodbye("Goodbye, CMake World");

  std::cout << say_goodbye << std::endl;

  return EXIT_SUCCESS;
}

新建bulid目录，windows下编译：cmake -G"Unix Makefiles" ../，得到三个 libmessage的链接库。（Linux下编译一直报错，把hello-word.cpp换个名字，比如main.cpp，就好了）

运行

 参考：

add_library — CMake 3.22.4 Documentation