[C++知识库]CMake I 构建时生成源码

目录

1.python脚本

2.CMakeLists.txt

（1）file(MAKE_DIRECTORY [...])

3.调用生成的C++文件

4.配置

5.构建，生成源码

6.运行exe

????????能够在构建时生成源代码是实用开发人员工具箱中的一个强大功能，他们希望根据某些规则生成可能很长且具有竞争力的代码，同时避免在源代码存储库中显式跟踪生成的代码。例如，我们可以想象根据检测到的平台或体系结构生成不同的源代码。或者，我们可以使用Python的简单性，在构建时根据我们在配置步骤中收集的输入生成显式和高效的C++代码。

????????本文通过使用add_custom_command()函数执行python命令生成C++文件primes.hpp。

1.python脚本

????????generate.py 脚本接受两个命令行参数：一个整数范围和一个输出文件名。

"""
Generates C++ vector of prime numbers up to max_number
using sieve of Eratosthenes.
"""
import pathlib
import sys

#参数1
max_number = int(sys.argv[-2])
#参数2
output_file_name = pathlib.Path(sys.argv[-1])

numbers = range(2, max_number + 1)
is_prime = {number: True for number in numbers}

for number in numbers:
    current_position = number
    if is_prime[current_position]:
        while current_position <= max_number:
            current_position += number
            is_prime[current_position] = False
#存放质数
primes = (number for number in numbers if is_prime[number])

code = """#pragma once

#include <vector>

const std::size_t max_number = {max_number};

std::vector<int> & primes() {{
  static std::vector<int> primes;

{push_back}

  return primes;
}}
"""
push_back = '\n'.join(['  primes.push_back({:d});'.format(x) for x in primes])
output_file_name.write_text(
    code.format(max_number=max_number, push_back=push_back))

2.CMakeLists.txt

????????注意python软件需要安装python3。

（1）file(MAKE_DIRECTORY [<directories>...])

file(MAKE_DIRECTORY [<directories>...])

????????在指定目录处创建子目录，如果它们的父目录不存在，也会创建它们的父目录。

cmake_minimum_required(VERSION 3.5 FATAL_ERROR)

project(recipe-03 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

#检测Python解释器
find_package(PythonInterp QUIET REQUIRED)

#将生成的代码放在 ${CMAKE_CURRENT_BINARY_DIR}/generate 下
file(MAKE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/generated)

#质数上限
set(MAX_NUMBER "100" CACHE STRING "Upper bound for primes")

#定义一个自定义命令来生成头文件，它执行 generate.py 脚本，并接受 ${MAX_NUMBER} 和文件路径( ${CMAKE_CURRENT_BINARY_DIR}/generated/primes.hpp )作为参数
add_custom_command(
  OUTPUT
    ${CMAKE_CURRENT_BINARY_DIR}/generated/primes.hpp
  COMMAND
    ${PYTHON_EXECUTABLE} generate.py ${MAX_NUMBER} ${CMAKE_CURRENT_BINARY_DIR}/generated/primes.hpp
  WORKING_DIRECTORY
    ${CMAKE_CURRENT_SOURCE_DIR}
  DEPENDS
    generate.py
  )

#定义可执行文件及其目标，包括目录和依赖关系
add_executable(example "")

target_sources(example
  PRIVATE
    example.cpp
    ${CMAKE_CURRENT_BINARY_DIR}/generated/primes.hpp
  )

target_include_directories(example
  PRIVATE
    ${CMAKE_CURRENT_BINARY_DIR}/generated
  )

3.调用生成的C++文件

#include "primes.hpp"

#include <iostream>
#include <vector>

int main() {
  std::cout << "all prime numbers up to " << max_number << ":";

  for (auto prime : primes())
    std::cout << " " << prime;

  std::cout << std::endl;

  return 0;
}

4.配置

5.构建，生成源码

生成的primes.hpp：

#pragma once

#include <vector>

const std::size_t max_number = 100;

std::vector<int> & primes() {
  static std::vector<int> primes;

  primes.push_back(2);
  primes.push_back(3);
  primes.push_back(5);
  primes.push_back(7);
  primes.push_back(11);
  primes.push_back(13);
  primes.push_back(17);
  primes.push_back(19);
  primes.push_back(23);
  primes.push_back(29);
  primes.push_back(31);
  primes.push_back(37);
  primes.push_back(41);
  primes.push_back(43);
  primes.push_back(47);
  primes.push_back(53);
  primes.push_back(59);
  primes.push_back(61);
  primes.push_back(67);
  primes.push_back(71);
  primes.push_back(73);
  primes.push_back(79);
  primes.push_back(83);
  primes.push_back(89);
  primes.push_back(97);

  return primes;
}

6.运行exe