VSCode下C++ unordered_map列表初始化编译错误求助

问题描述 #

尝试用初始化列表初始化unordered_map，代码如下：

const unordered_map <int, int> prova = 
{
    {0,1},
    {4,2}
};

在VSCode内编译时持续报错：
error: non-aggregate type 'const unordered_map<int, int>' cannot be initialized with an initializer list

已在c_cpp_properties.json中配置-std=c++20，并尝试多种编译器组合，结果一致。但终端执行g++ -std=c++20 -o prova prova.cpp编译正常，省略-std=c++20则出现相同错误。

系统环境 #

g++ --version输出：

Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/4.2.1 Apple clang version 13.0.0 (clang-1300.0.29.30) Target: x86_64-apple-darwin20.6.0 Thread model: posix InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

VSCode配置 #

• .vscode/settings.json为空
• .vscode/c_cpp_properties.json：

{
    "configurations": [
        {
            "name": "Mac",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "macFrameworkPath": [
                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks"
            ],
            "compilerPath": "/usr/bin/g++",
            "cStandard": "c17",
            "cppStandard": "c++20",
            "intelliSenseMode": "macos-clang-x64",
            "compilerArgs": [
                "-std=c++20"
            ]
        }
    ],
    "version": 4
}

• .vscode/tasks.json：

{
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: clang++ compila il file attivo",
            "command": "/usr/bin/clang++",
            "args": [
                "-fcolor-diagnostics",
                "-fansi-escape-codes",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "Attività generata dal debugger."
        }
    ],
    "version": "2.0.0"
}

问题原因 #

c_cpp_properties.json中的配置仅用于IntelliSense代码提示，不会作用于实际编译过程。VSCode默认的编译任务（tasks.json）里没有添加-std=c++20参数，导致编译器以旧C++标准编译，而旧标准下无法用初始化列表正确初始化const unordered_map。终端编译时手动指定了-std=c++20，因此能正常通过。

解决方法 #

修改.vscode/tasks.json，在编译参数args数组中加入-std=c++20：

{
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: clang++ compila il file attivo",
            "command": "/usr/bin/clang++",
            "args": [
                "-fcolor-diagnostics",
                "-fansi-escape-codes",
                "-g",
                "-std=c++20", // 添加该行启用C++20标准
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "Attività generata dal debugger."
        }
    ],
    "version": "2.0.0"
}

如果偏好使用g++编译，可将command字段改为/usr/bin/g++，其余参数无需调整。

内容的提问来源于stack exchange，提问作者user13407848