有效地 const_cast-ing 常量引用参数
我有一个成员函数，它接受另一个对象的常量引用参数。我想 const_cast 这个参数以便在成员函数中轻松使用它。为此，以下哪个代码更好？：
void AClass::AMember(const BClass & _BObject)
{
// FORM #1 - Cast as an object:
BClass BObject = const_cast<BClass &>(_BObject);
// ...
}
void AClass::AMember(const BClass & _BObject)
{
// FORM #2 - Cast as a reference:
BClass & BObject = const_cast<BClass &>(_BObject);
// ...
}
您能比较一下这两种形式吗？在速度和内存使用方面哪一个更好？
I have a member function which takes a constant reference parameter to another object. I want to const_cast this parameter in order to easily use it inside the member function. For this purpose, which of the following codes is better?:
void AClass::AMember(const BClass & _BObject)
{
// FORM #1 - Cast as an object:
BClass BObject = const_cast<BClass &>(_BObject);
// ...
}
void AClass::AMember(const BClass & _BObject)
{
// FORM #2 - Cast as a reference:
BClass & BObject = const_cast<BClass &>(_BObject);
// ...
}
Can you please compare these two forms? Which one is better in criteria of speed and memory usage?
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评论（2）
第一个没有任何意义，因为您放弃了
_BObject的常量，只是稍后将其作为常量引用传递给BClass构造函数并创建一个副本，B对象。第二个实现了它的意思——抛弃常量并保留对原始对象的引用。所以如果你问我，第二个更好。但请注意，const_cast并不总是安全的。The first one doesn't make any sense as you cast away constness of
_BObjectto only later pass it as a constant reference toBClassconstructor and create a copy,BObject. The second one does what it means - casts away the constness and keeps the reference to the original object. So if you ask me, the second one is better. Be aware though thatconst_castis not always safe.第一个版本制作对象的副本。第二个版本没有。所以第二个版本会更快，除非你想复制。
顺便说一句，所有以下划线开头后跟大写字母的标识符都保留供编译器使用。您不应该使用像
_BObject这样的变量名称。The first version makes a copy of the object. The second version doesn't. So the second version will be faster unless you want to make a copy.
By the way, all identifiers that start with an underscore followed by a capital letter are reserved for use by the compiler. You should not be using variable names like
_BObject.