检测处理器指令集

这里使用的大致方法一致，我们在源码中要输出一些指示处理器指令集的信息，但这些信息的define既没有在源码中给出也没有在CMakeLists中直接指明定义，而是通过间接生成头文件的形式被包含。

#include "config.h"

#include <cstdlib>
#include <iostream>

int main() {
  std::cout << "Number of logical cores: " << NUMBER_OF_LOGICAL_CORES << std::endl;
  std::cout << "Number of physical cores: " << NUMBER_OF_PHYSICAL_CORES << std::endl;

  std::cout << "Total virtual memory in megabytes: " << TOTAL_VIRTUAL_MEMORY
            << std::endl;
  std::cout << "Available virtual memory in megabytes: " << AVAILABLE_VIRTUAL_MEMORY
            << std::endl;
  std::cout << "Total physical memory in megabytes: " << TOTAL_PHYSICAL_MEMORY
            << std::endl;
  std::cout << "Available physical memory in megabytes: "
            << AVAILABLE_PHYSICAL_MEMORY << std::endl;

  std::cout << "Processor is 64Bit: " << IS_64BIT << std::endl;
  std::cout << "Processor has floating point unit: " << HAS_FPU << std::endl;
  std::cout << "Processor supports MMX instructions: " << HAS_MMX << std::endl;
  std::cout << "Processor supports Ext. MMX instructions: " << HAS_MMX_PLUS
            << std::endl;
  std::cout << "Processor supports SSE instructions: " << HAS_SSE << std::endl;
  std::cout << "Processor supports SSE2 instructions: " << HAS_SSE2 << std::endl;
  std::cout << "Processor supports SSE FP instructions: " << HAS_SSE_FP << std::endl;
  std::cout << "Processor supports SSE MMX instructions: " << HAS_SSE_MMX
            << std::endl;
  std::cout << "Processor supports 3DNow instructions: " << HAS_AMD_3DNOW
            << std::endl;
  std::cout << "Processor supports 3DNow+ instructions: " << HAS_AMD_3DNOW_PLUS
            << std::endl;
  std::cout << "IA64 processor emulating x86 : " << HAS_IA64 << std::endl;

  std::cout << "OS name: " << OS_NAME << std::endl;
  std::cout << "OS sub-type: " << OS_RELEASE << std::endl;
  std::cout << "OS build ID: " << OS_VERSION << std::endl;
  std::cout << "OS platform: " << OS_PLATFORM << std::endl;

  return EXIT_SUCCESS;
}

注意以下的cpp源文件目录下最初没有config.h这个文件。而在目录中存在一个config.h.in的文件，如下：

#pragma once
// 这个文件用于生成 config.h 这个文件， 在编译的过程中动态生成
#define NUMBER_OF_LOGICAL_CORES   @_NUMBER_OF_LOGICAL_CORES@
#define NUMBER_OF_PHYSICAL_CORES  @_NUMBER_OF_PHYSICAL_CORES@
#define TOTAL_VIRTUAL_MEMORY      @_TOTAL_VIRTUAL_MEMORY@
#define AVAILABLE_VIRTUAL_MEMORY  @_AVAILABLE_VIRTUAL_MEMORY@
#define TOTAL_PHYSICAL_MEMORY     @_TOTAL_PHYSICAL_MEMORY@
#define AVAILABLE_PHYSICAL_MEMORY @_AVAILABLE_PHYSICAL_MEMORY@
#define IS_64BIT                  @_IS_64BIT@
#define HAS_FPU                   @_HAS_FPU@
#define HAS_MMX                   @_HAS_MMX@
#define HAS_MMX_PLUS              @_HAS_MMX_PLUS@
#define HAS_SSE                   @_HAS_SSE@
#define HAS_SSE2                  @_HAS_SSE2@
#define HAS_SSE_FP                @_HAS_SSE_FP@
#define HAS_SSE_MMX               @_HAS_SSE_MMX@
#define HAS_AMD_3DNOW             @_HAS_AMD_3DNOW@
#define HAS_AMD_3DNOW_PLUS        @_HAS_AMD_3DNOW_PLUS@
#define HAS_IA64                  @_HAS_IA64@
#define OS_NAME                  "@_OS_NAME@"
#define OS_RELEASE               "@_OS_RELEASE@"
#define OS_VERSION               "@_OS_VERSION@"
#define OS_PLATFORM              "@_OS_PLATFORM@"

该文件将结合CMakeLists文件，在cmake阶段动态生成我们源文件中所需要引用的头文件config.h，CMakeLists文件如下：

cmake_minimum_required(VERSION 3.10 FATAL_ERROR)

project(recipe-05 LANGUAGES CXX)

add_executable(processor-info "")

target_sources(processor-info
  PRIVATE
    processor-info.cpp
  )

target_include_directories(processor-info
  PRIVATE
    ${PROJECT_BINARY_DIR}
  )
  // PROJECT_BINARY_DIR 这里指的就是 build这个文件夹， 也就是你生成编译文件的路径
  // 同样的，你的config.h.in生成的config.h就放在build文件夹下
  // 所以你要引入这个路径作为包含路径


  // 查询主机系统的信息，获取一些关键字:
foreach(key
  IN ITEMS
    NUMBER_OF_LOGICAL_CORES
    NUMBER_OF_PHYSICAL_CORES
    TOTAL_VIRTUAL_MEMORY
    AVAILABLE_VIRTUAL_MEMORY
    TOTAL_PHYSICAL_MEMORY
    AVAILABLE_PHYSICAL_MEMORY
    IS_64BIT
    HAS_FPU
    HAS_MMX
    HAS_MMX_PLUS
    HAS_SSE
    HAS_SSE2
    HAS_SSE_FP
    HAS_SSE_MMX
    HAS_AMD_3DNOW
    HAS_AMD_3DNOW_PLUS
    HAS_IA64
    OS_NAME
    OS_RELEASE
    OS_VERSION
    OS_PLATFORM
  )
  cmake_host_system_information(RESULT _${key} QUERY ${key})
endforeach()
// 注意这个语句cmake_host_system_information()
// RESULT关键字后面根一个自定义的变量名 variable
// QUERY后面跟一个系统中要查询的key值
// 结果是将查询到的key值赋值给前面的自定义变量中 

configure_file(config.h.in config.h @ONLY)
// 以上存储在自定义变量中的值将作为最终值被添加到config.h文件的define宏定义中（用于生成.h文件）