Learn muduo - Part 10 C++ Compiler Link Model Essentials

muduo: https://github.com/chenshuo/muduo

本系列是 《Linux 多线程服务端编程：使用 muduo C++ 网络库》 学习笔记。

Part 10: C++ 编译链接模型精要

重载决议小例子

C/C++ 可以看做采用 one pass 编译，解析语义时只能基于前面已经解析出的语义。比如：

#include <iostream>

using namespace std::literals;

void foo(int i) {
    std::cout << "int" << std::endl;
}

void bar() {
    foo('a');
}

void foo(char i) {
    std::cout << "char" << std::endl;
}

int main() {
    bar();
    return 0;
}

结果输出 int 而不是 char。

检查头文件引入小技巧

头文件 include 具有传染性。

假如有这样的例子：

#include <iostream>

int main() {
    std::string s = "Hello World";
    return 0;
}

头文件 <string> 并未被直接 include，但仍能编译通过。有个小技巧可以检查其是如何被 include 进来的，原理是在当前目录创建一个 string 文件，故意制造编译错误。

步骤如下：

1. 创建一个指示编译失败的 string 文件。

   $ cat > string
   #error error
   ^D

2. 编译

   $ g++ -M -I . test.cc
   In file included from test.cc:1:
   In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:37:
   In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:214:
   In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15:
   ./string:1:2: error: error
   #error error

可见头文件 <string> 是在 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15 处被 include 的。