在结构中初始化默认值 [英] Initializing default values in a struct

问题描述

如果我需要初始化一个C ++结构的几个选择值，这将是正确的：

If I needed to initialize only a few select values of a C++ struct, would this be correct:

struct foo {
    foo() : a(true), b(true) {}
    bool a;
    bool b;
    bool c;
 } bar;

我认为我最终会得到一个 struct 项目 bar 与元素 bar.a = true ， bar.b = true 和未定义的 bar.c ？

Am I correct to assume I would end up with one struct item called bar with elements bar.a = true, bar.b = true and an undefined bar.c?

推荐答案

是的。 bar.a 和 bar.b 设置为true，但 bar.c 未定义。

Yes. bar.a and bar.b are set to true, but bar.c is undefined. However, certain compiler will set it to false.

查看实例： struct demo

根据C ++标准第8.5.12节：

According to C++ standard Section 8.5.12:

if不执行初始化，具有自动或动态存储持续时间的
对象具有不确定的值

if no initialization is performed, an object with automatic or dynamic storage duration has indeterminate value

对于原始内置数据类型（ bool ，char，wchar_t，short，int，long，float，double，long double），只有全局变量它们没有显式初始化。

For primitive built-in data types (bool, char, wchar_t, short, int, long, float, double, long double), only global variables (all static storage variables) get default value of zero if they are not explicitly initialized.

如果你不想要未定义的 bar.c 也应该像对 bar.a 和 bar.b 一样进行初始化。

If you don't really want undefined bar.c to start with, you should also initialize it like you did for bar.a and bar.b.

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