c++ - C++11 中引入了哪些重大变化？

Question

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()，替换旧实例运算符 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，但它仍然是一个重大变化:过去有效的程序不再有效。

还有其他重大变化吗？

Answer 1

FDIS 在附录中有一个不兼容部分 C.2 “C++ 和 ISO C++ 2003”。

总结，在这里解释 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性，我并不完全了解它们的含义，所以我将这些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"; // 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.

(不可否认，对于大多数人来说，这并不是真正的兼容性问题)。

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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.

我的例子:

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

这种 sizeof 技巧已经被一些 SFINAE 使用，现在需要改变:)

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User-declared destructors have an implicit exception specification.

我的例子:

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

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

此代码调用 terminate在 C++0x 中，但在 C++03 中没有。因为 A::~A 的隐式异常规范在 C++0x 中是 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.

在 C++03 中，>>将始终是移位运算符标记。

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Allow dependent calls of functions with internal linkage.

我的例子:

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

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

int main() { g(0); }

在 C++03 中，这调用 f(long) , 但在 C++0x 中，这调用 f(int) .需要注意的是，在C++03和C++0x中，下面调用f(B) (实例化上下文仍然只考虑外部链接声明)。

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); }

更好的匹配f(A)没有被采纳，因为它没有外部链接。

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库变化

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.