const_cast conversion
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不同的简历，资格类型之间转换.
Original:
Converts between types with different cv-qualification.
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目录 |
[编辑] 语法
const_cast < new_type > ( expression )
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返回值类型
new_typeOriginal:
Returns a value of type
new_type.The text has been machine-translated via Google Translate.
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[编辑] 解释
只有下面的转换可以做const_cast。尤其是，仅可用于const_cast抛弃（删除）常量性或波动性.
Original:
Only the following conversions can be done with const_cast. In particular, only const_cast may be used to cast away (remove) constness or volatility.
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1)
两个可能相同类型的多级指针可以相互间的转换，不管cv修饰符在每个级别.
Original:
Two possibly multilevel pointers to the same type may be converted between each other, regardless of cv-qualifiers at each level.
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2)
任何类型的
T左值可能会被转换到一个左值或rvalue引用到相同类型T，更多或更少的cv限定。同样地，一个rvalue可被转换成一个或多或少cv限定rvalue引用.Original:
lvalue of any type
T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified. Likewise, an rvalue may be converted to a more or less cv-qualified rvalue reference.The text has been machine-translated via Google Translate.
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3)
规则同样适用于可能是多层次的数据成员的指针.
Original:
Same rules apply to possibly multilevel pointers to data members.
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4)
空指针值可转换为空指针值的new_type
Original:
null pointer value may be converted to the null pointer value of new_type
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与所有的强制转换表达式，其结果是：
Original:
As with all cast expressions, the result is:
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- 如果一个左值new_type是一个左值引用类型或一个右值引用为函数类型Original:an lvalue if new_type is an lvalue reference type or an rvalue reference to function type;The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions. - 值为xValue，如果new_type是一个右值引用的对象类型Original:an xvalue if new_type is an rvalue reference to object type;The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions. - 一个prvalue否则.Original:a prvalue otherwise.The text has been machine-translated via Google Translate.
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[编辑] 注释
函数指针和成员函数的指针是不受到const_cast
Original:
Pointers to functions and pointers to member functions are not subject to const_cast
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即使const_cast可以删除任何指针常量性或参考，使用指针或引用写的对象被宣布const调用未定义的行为.
Original:
Even though const_cast may remove constness from any pointer or reference, using the resulting pointer or reference to write to an object that was declared const invokes undefined behavior.
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[编辑] 关键字
[编辑] 为例
#include <iostream> struct type { type() :i(3) {} void m1(int v) const { // this->i = v; // compile error: this is a pointer to const const_cast<type*>(this)->i = v; // OK } int i; }; int main() { int i = 3; // i is not declared const const int& cref_i = i; const_cast<int&>(cref_i) = 4; // OK: modifies i std::cout << "i = " << i << '\n'; type t; t.m1(4); std::cout << "type::i = " << t.i << '\n'; const int j = 3; // j is declared const int* pj = const_cast<int*>(&j); *pj = 4; // undefined behavior! void (type::*mfp)(int) const = &type::m1; // pointer to member function // const_cast<void(type::*)(int)>(mfp); // compiler error: const_cast does not // work on function pointers }
Output:
i = 4 type::i = 4
