在联合中使用继承 [英] Using inheritance within a union

问题描述

我想知道是否有人知道是否可以以某种方式在联合中使用继承.

在下面的示例中，TestFails 联合将不包含 Base 结构中的 a 变量，而 TestWorks 确实有效.

struct Base { int a;};联合测试失败{结构:公共基础{}；国际b;};联合测试工厂{结构{ int a;};国际b;};int main(){TestWorks 有效；作品.a = 0;TestFails 失败；失败.a = 0;返回0；}

您可以在这里测试代码:http://ideone.com/dUzpOR

解决方案

首先 - 您认为 TestWorks 有效的假设是错误的.这不是标准的 C++ - 只是它的扩展 - 它被称为 无名匿名struct - 当您使用迂腐选项进行编译时，您会得到:

<块引用>

prog.cc:5:27: 错误:ISO C++ 禁止匿名结构 [-Wpedantic]
结构:公共基础{};

<代码> ^

<块引用>

prog.cc:11:22: 错误:ISO C++ 禁止匿名结构 [-Wpedantic]
结构{ int a;};

要解决您的问题 - 只需命名这些匿名结构:

union TestFails{结构体:公共基础 {} s；//^国际b;};联合测试工厂{结构{ int a;} s;//^国际b;};

I was was wondering if anyone knows if it's possible to use inheritance within a union somehow.

In the example below, the TestFails union will not contain the a variable within the Base struct, while TestWorks does work.

struct Base { int a; };

union TestFails
{
    struct : public Base {};
    int b;
};

union TestWorks
{
    struct  { int a; };
    int b;
};

int main()
{
    TestWorks works;
    works.a = 0;

    TestFails fails;
    fails.a = 0;

    return 0;
}

You can test the code here: http://ideone.com/dUzpOR

解决方案

First of all - your assumption that TestWorksworks is wrong. This is not standard C++ - only extension to it - it is called unnamed anonymous struct - and when you compile with pedantic options you get:

prog.cc:5:27: error: ISO C++ prohibits anonymous structs [-Wpedantic]
struct : public Base {};

                       ^

prog.cc:11:22: error: ISO C++ prohibits anonymous structs [-Wpedantic]
struct { int a; };

To solve your issue - just name these anonymous structs:

union TestFails
{
    struct : public Base {} s;
    //                      ^
    int b;
};

union TestWorks
{
    struct  { int a; } s;
    //                 ^
    int b;
};

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