问题

在Linux主机或Docker环境下，使用 VS Code 编写 CPP 代码时，变量没有代码补全。

解决方案

首先确保已经安装并启用了 C++ 扩展3件套：C/C++、C/C++ Themes、CMake Tools 。
确保设置中的 C_CPP: Intelli Sense Engine 选项为 default ，即开启状态。
在 VS Code 的项目根目录下找到 .vscode 文件夹，若没有可创建此文件夹。
在 .vscode 文件夹中新建文件：c_cpp_properties.json，编写配置如下：

{"configurations": [{"name": "Linux","compilerPath": "/usr/bin/gcc","intelliSenseMode": "linux-gcc-x64"}],"version": 4
}

若 .vscode 文件夹中已存在 settings.json 文件，则无需更改；若不存在，可新建此文件，编写配置如下（可自行修改配置）：

{"files.associations": {"*.inc": "cpp","array": "cpp","bitset": "cpp","string_view": "cpp","initializer_list": "cpp","ranges": "cpp","span": "cpp","regex": "cpp","utility": "cpp","valarray": "cpp","any": "cpp","atomic": "cpp","barrier": "cpp","bit": "cpp","*.tcc": "cpp","cctype": "cpp","cfenv": "cpp","charconv": "cpp","chrono": "cpp","cinttypes": "cpp","clocale": "cpp","cmath": "cpp","codecvt": "cpp","compare": "cpp","complex": "cpp","concepts": "cpp","condition_variable": "cpp","coroutine": "cpp","csetjmp": "cpp","csignal": "cpp","cstdarg": "cpp","cstddef": "cpp","cstdint": "cpp","cstdio": "cpp","cstdlib": "cpp","cstring": "cpp","ctime": "cpp","cuchar": "cpp","cwchar": "cpp","cwctype": "cpp","deque": "cpp","forward_list": "cpp","list": "cpp","map": "cpp","set": "cpp","string": "cpp","unordered_map": "cpp","unordered_set": "cpp","vector": "cpp","exception": "cpp","algorithm": "cpp","functional": "cpp","iterator": "cpp","memory": "cpp","memory_resource": "cpp","netfwd": "cpp","numeric": "cpp","optional": "cpp","random": "cpp","ratio": "cpp","source_location": "cpp","system_error": "cpp","tuple": "cpp","type_traits": "cpp","fstream": "cpp","future": "cpp","iomanip": "cpp","iosfwd": "cpp","iostream": "cpp","istream": "cpp","latch": "cpp","limits": "cpp","mutex": "cpp","new": "cpp","numbers": "cpp","ostream": "cpp","scoped_allocator": "cpp","semaphore": "cpp","shared_mutex": "cpp","sstream": "cpp","stdexcept": "cpp","stop_token": "cpp","streambuf": "cpp","syncstream": "cpp","thread": "cpp","typeindex": "cpp","typeinfo": "cpp","variant": "cpp"},// "files.autoSave": "afterDelay","files.trimTrailingWhitespace": true,"files.insertFinalNewline": true,"editor.tabSize": 2,"cmake.configureOnOpen": false,"C_Cpp.formatting": "clangFormat","C_Cpp.clang_format_style": "LLVM"
}

保存好配置文件后，重启 VS Code 打开项目，即可修复自动补全功能。