在 C++ 中，内置类型的简单初始化是否不受静态初始化顺序失败的影响？

Question

我知道 C++ 中的 static initialization order fiasco 和 construct on first use idiom 避免它。因此在下面的代码中 a 的全局分配可能发生在 foo::a 之前，所以 a 的值未定义。另一方面，全球 b 的赋值是可以的，因为它调用了函数 foo::b().

#include <iostream>
#include <string>

using namespace std;

// foo.hpp

class foo {
public:
  static const string a;
  static const string& b();
  static const char* const c;
  static const char* const d[2];
  static const int e;
  static const int f[2];
};

// foo.cpp

const string foo::a("astr");
const string& foo::b() {
  static const string t("bstr");
  return t;
}
const char* const foo::c = "cstr";
const char* const foo::d[2] = {"dstr1", "dstr2"};
const int foo::e = 5;
const int foo::f[2] = {6, 7};

// main.cpp

// global initializations
string a = foo::a;              // dangerous, might be "" or "astr"
string b = foo::b();            // safe, guaranteed to be "bstr"
const char* c = foo::c;         // what about these...?
const char* d = foo::d[0];
int e = foo::e;
int f = foo::f[0];

int main() {
  cout << a << " " << b << "\n"
       << c << " " << d << "\n"
       << e << " " << f << "\n";
}

（假设我在这里合并了 foo.hpp、foo.cpp 和 main.cpp。）但是，作为内置类型或它们的数组的变量呢？因此，c、d、e 和 f 的全局赋值在此代码中安全吗？链接器似乎可以为这些变量设置内存所以不需要在运行时间进行初始化。但我能依靠吗这个？

我知道我不应该使用全局变量。然而我是作者库（foo.cpp 和 foo.hpp），我无法控制我图书馆的用户（main.cpp 的作者）有。

Answer 1

这里的关键是“static 初始化”（使用标准语言正式称为具有静态存储持续时间 的对象的动态初始化）之间的区别排序失败）和静态初始化.

标准说（第 [basic.start.static] 节）

A constant initializer for an object o is an expression that is a constant expression, except that it may also invoke constexpr constructors for o and its subobjects even if those objects are of non-literal class types. [ Note: Such a class may have a non-trivial destructor — end note ]

Constant initialization is performed:

if each full-expression (including implicit conversions) that appears in the initializer of a reference with static or thread storage duration is a constant expression and the reference is bound to a glvalue designating an object with static storage duration, to a temporary object or subobject thereof, or to a function;

if an object with static or thread storage duration is initialized by a constructor call, and if the initialization full-expression is a constant initializer for the object;

if an object with static or thread storage duration is not initialized by a constructor call and if either the object is value-initialized or every full-expression that appears in its initializer is a constant expression.

If constant initialization is not performed, a variable with static storage duration or thread storage duration is zero-initialized. Together, zero-initialization and constant initialization are called static initialization; all other initialization is dynamic initialization. Static initialization shall be performed before any dynamic initialization takes place.

您的 c、d、e 和 f 对象具有常量初始化器，因此它们的初始化在静态初始化阶段完成（即使 c 和 d 本身不是常量），并且它们的值在所有动态初始化期间都是可用的，即使是那些之前词法出现的值。

在 C++ 中，内置类型的简单初始化是否不受静态初始化顺序失败的影响？

In C++ are simple initializations of built-in type immune to the static initialization order fiasco?

c++

static-initialization

static-order-fiasco