如何解决VSCode / g++无法识别默认包含文件的问题？

Question

我对C++的编码非常陌生，几乎没有任何经验。我的问题是:我想使用字符串，所以我在代码中添加了#include，但是VSCode告诉我identifier "string" is undefinedC/C++(20)。我所做的是添加和修改一个c_cpp_properties.json文件vor VSCode：

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**",
                "/usr/include/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "gnu17",
            "cppStandard": "gnu++14",
            "intelliSenseMode": "linux-gcc-x64"
        }
    ],
    "version": 4
}

但这并没有解决问题。另外，我已经确保安装了C++，包括g++编译器。在VSCode中，我使用以下C++插件/加载项: C/C++和C/C++项目生成器(我并不真正使用)。这是我代码的相关部分：

#include <iostream>
#include <string>

int main(int argc, char *argv[])
{
string s;

return 0;
}

这是错误日志/调试消息：

g++ -std=c++17 -Wall -Wextra -g -Iinc -c src/main.cpp  -o src/main.o
src/main.cpp: In function ‘int main(int, char**)’:
src/main.cpp:30:2: error: ‘string’ was not declared in this scope
   30 |  string s;
      |  ^~~~~~
src/main.cpp:30:2: note: suggested alternatives:
In file included from /usr/include/c++/9/iosfwd:39,
                 from /usr/include/c++/9/ios:38,
                 from /usr/include/c++/9/ostream:38,
                 from /usr/include/c++/9/iostream:39,
                 from src/main.cpp:1:
/usr/include/c++/9/bits/stringfwd.h:79:33: note:   ‘std::string’
   79 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
In file included from /usr/include/c++/9/bits/locale_classes.h:40,
                 from /usr/include/c++/9/bits/ios_base.h:41,
                 from /usr/include/c++/9/ios:42,
                 from /usr/include/c++/9/ostream:38,
                 from /usr/include/c++/9/iostream:39,
                 from src/main.cpp:1:
/usr/include/c++/9/string:67:11: note:   ‘std::pmr::string’
   67 |     using string    = basic_string<char>;
      |           ^~~~~~

解决方案:将string s;替换为std::string s;。

Answer 1

C++字符串在std命名空间中“隐藏”。因为这一点，编译器无法识别string。

您可以包含整个std命名空间：

using namespace std;

对特定的字符串执行此操作，而不执行任何其他操作：

using std::string;

或在初始化字符串时键入std::string而不是string。默认情况下，C++标准库在编译器的包含路径中，您不需要做任何额外的事情就可以使用它的头部。