C++11 引入了哪些重大变化? [英] What breaking changes are introduced in C++11?

问题描述

我知道C++11中至少有一个变化会导致一些旧代码停止编译:在标准库中引入explicit operator bool()，替换旧实例operator void*().诚然，这将破坏的代码可能是一开始就不应该有效的代码，但它仍然是一个破坏性的变化:曾经有效的程序不再有效.

还有其他重大变化吗?

解决方案

FDIS 在附录 C.2C++ 和 ISO C++ 2003"中有一个不兼容部分.

总结，在此处解释 FDIS，使其(更好)适合作为 SO 答案.我添加了一些我自己的例子来说明差异.

有一些与库相关的不兼容问题，我不完全知道其中的含义，因此我将这些问题留给其他人详细说明.

核心语言

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#define u8 "abc"const char *s = u8"def";//以前是abcdef"，现在是def"

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#define _x "那里""hello"_x//现在是用户定义的字符串文字.以前，扩展 _x .

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新关键字:alignas、alignof、char16_t、char32_t、constexpr、decltype、noexcept、nullptr、static_assert 和 thread_local

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某些大于 long 可以表示的整数文字可以从无符号整数类型更改为有符号 long long.

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使用整数除法的有效 C++ 2003 代码将结果向 0 或向负无穷大舍入，而 C++0x 总是向 0 舍入.

(诚然，对于大多数人来说，这并不是真正的兼容性问题).

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使用关键字 auto 作为存储类说明符的有效 C++ 2003 代码在 C++0x 中可能无效.

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缩小转换会导致与 C++03 不兼容.例如，以下代码在 C++ 2003 中有效，但在本国际标准中无效，因为 double 到 int 是一种收缩转换:

int x[] = { 2.0 };

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当隐式定义格式错误时，隐式声明的特殊成员函数被定义为已删除.

一个有效的 C++ 2003 程序在不需要定义的上下文中使用这些特殊成员函数之一(例如，在没有潜在评估的表达式中)变得格式错误.

我的例子:

struct A { private: A();};结构 B : A { };int main() { sizeof B();/* 在 C++03 中有效，在 C++0x 中无效 */}

一些SFINAE已经使用了这种sizeof技巧，现在需要更改:)

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用户声明的析构函数具有隐式异常规范.

我的例子:

struct A {~A() { 抛出foo"；}};int main() { 尝试 { A a;} 抓住(...) { } }

此代码在 C++0x 中调用 terminate，但在 C++03 中不调用.因为C++0x中A::~A的隐式异常规范是noexcept(true).

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包含 export 的有效 C++ 2003 声明在 C++0x 中格式错误.

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包含 > 后紧跟另一个 > 的有效 C++ 2003 表达式现在可以被视为关闭两个模板.

在 C++03 中，>> 将始终是移位运算符标记.

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允许依赖调用具有内部链接的函数.

我的例子:

static void f(int) { }void f(long) { }模板void g(T t) { f(t);}int main() { g(0);}

在 C++03 中，它调用 f(long)，但在 C++0x 中，它调用 f(int).需要注意的是，在C++03和C++0x中，以下调用f(B)(实例化上下文仍然只考虑extern链接声明).

struct B { };结构 A : B { };模板void g(T t) { f(t);}静态无效 f(A) { }无效 f(B) { }int main() { A a;克(一)；}

更好的匹配f(A)没有取，因为它没有外部链接.

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库变化

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使用添加到 C++ 标准的任何标识符的有效 C++ 2003 代码C++0x 库可能无法编译或在本国际标准中产生不同的结果.

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#includes 标头和新 C++0x 标准库标头名称的有效 C++ 2003 代码在本国际标准中可能无效.

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已编译预期交换位于 中的有效 C++ 2003 代码可能必须改为包含

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全局命名空间 posix 现在保留用于标准化.

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将 override、final、carries_dependency 或 noreturn 定义为宏的有效 C++ 2003 代码在C++0x.

I know that at least one of the changes in C++11 that will cause some old code to stop compiling: the introduction of explicit operator bool() in the standard library, replacing old instances of operator void*(). Granted, the code that this will break is probably code that should not have been valid in the first place, but it's still a breaking change nonetheless: programs that used to be valid no longer are.

Are there any other breaking changes?

解决方案

The FDIS has a section for incompatibilities, at appendix C.2 "C++ and ISO C++ 2003".

Summary, paraphrasing the FDIS here, to make it (better) suitable as a SO answer. I added some examples of my own to illustrate the differences.

There are a few library-related incompatibilities where I don't exactly know the implications of, so I leave those for others to elaborate on.

Core language

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#define u8 "abc"
const char *s = u8"def"; // Previously "abcdef", now "def"

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#define _x "there"
"hello"_x // now a user-defined-string-literal. Previously, expanded _x .

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New keywords: alignas, alignof, char16_t, char32_t, constexpr, decltype, noexcept, nullptr, static_assert, and thread_local

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Certain integer literals larger than can be represented by long could change from an unsigned integer type to signed long long.

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Valid C++ 2003 code that uses integer division rounds the result toward 0 or toward negative infinity, whereas C++0x always rounds the result toward 0.

(admittedly not really a compatibility problem for most people).

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Valid C++ 2003 code that uses the keyword auto as a storage class specifier may be invalid in C++0x.

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Narrowing conversions cause incompatibilities with C++03. For example, the following code is valid in C++ 2003 but invalid in this International Standard because double to int is a narrowing conversion:

int x[] = { 2.0 };

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Implicitly-declared special member functions are defined as deleted when the implicit definition would have been ill-formed.

A valid C++ 2003 program that uses one of these special member functions in a context where the definition is not required (e.g., in an expresion that is not potentially evaluated) becomes ill-formed.

Example by me:

struct A { private: A(); };
struct B : A { };
int main() { sizeof B(); /* valid in C++03, invalid in C++0x */ }

Such sizeof tricks have been used by some SFINAE, and needs to be changed now :)

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User-declared destructors have an implicit exception specification.

Example by me:

struct A {
  ~A() { throw "foo"; }
};

int main() { try { A a; } catch(...) { } }

This code calls terminate in C++0x, but does not in C++03. Because the implicit exception specification of A::~A in C++0x is noexcept(true).

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A valid C++ 2003 declaration containing export is ill-formed in C++0x.

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A valid C++ 2003 expression containing > followed immediately by another > may now be treated as closing two templates.

In C++03, >> would always be the shift-operator token.

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Allow dependent calls of functions with internal linkage.

Example by me:

static void f(int) { }
void f(long) { }

template<typename T>
void g(T t) { f(t); }

int main() { g(0); }

In C++03, this calls f(long), but in C++0x, this calls f(int). It should be noted that in both C++03 and C++0x, the following calls f(B) (the instantiation context still only considers extern linkage declarations).

struct B { };
struct A : B { };

template<typename T>
void g(T t) { f(t); }

static void f(A) { }
void f(B) { }

int main() { A a; g(a); }

The better matching f(A) is not taken, because it does not have external linkage.

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Library changes

Valid C++ 2003 code that uses any identifiers added to the C++ standard library of C++0x may fail to compile or produce different results in This International Standard.

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Valid C++ 2003 code that #includes headers with names of new C++0x standard library headers may be invalid in this International Standard.

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Valid C++ 2003 code that has been compiled expecting swap to be in <algorithm> may have to instead include <utility>

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The global namespace posix is now reserved for standardization.

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Valid C++ 2003 code that defines override, final, carries_dependency, or noreturn as macros is invalid in C++0x.

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