Type Casting.docVIP

Type Casting 类型转换 Converting an expression of a given type into another type is known as type-casting. We have already seen some ways to type cast: 转换一个给定类型到其他类型的表达式被认为是“类型转换”。我们已经看到一些通向类型转换的途径： Implicit conversion 隐式转换 Implicit conversions do not require any operator. They are automatically performed when a value is copied to a compatible type. For example: 隐式转换的执行不需要任何操作符，当一个值复制到与其兼容类型的值时，隐式转换会自动执行。例如： 123 short a=2000; int b; b=a; Here, the value of a has been promoted from short to int and we have not had to specify any type-casting operator. This is known as a standard conversion. Standard conversions affect fundamental data types, and allow conversions such as the conversions between numerical types (short to int, int to float, double to int...), to or from bool, and some pointer conversions. Some of these conversions may imply a loss of precision, which the compiler can signal with a warning. This can be avoided with an explicit conversion. 这里，a的值将从短整型提升到整型，并且我不需要指定任何类型转换的操作符。这被认为是一种标准的转换。标准转换作用于基本数据类型，并且允许像这样的一些转换：从数值类型（short to int, int to float, double to int...）到bool两者之间的相互转换，以及一些指针的转换。编译器会对这些转换中有些可能隐含精度损失的转换预示警告，这是可以使用显示转换避免的。 Implicit conversions also include constructor or operator conversions, which affect classes that include specific constructors or operator functions to perform conversions. For example: 隐式转换也包含构造器或运算符的转换，这作用于包含指定构造器或操作符执行转换的功能的类。例如： 12345 class A {}; class B { public: B (A a) {} }; A a; B b=a; Here, a implicit conversion happened between objects of class A and class B, because B has a constructor that takes an object of class A as parameter. Therefore implicit conversions from A to B are allowed. 这里，一个隐式转换发生在类A和类B之间，因为B有一个取类A的一个对象作为参数的构造器。所以允许从A到B的隐式转换。 Explicit conversion 显示转换 C++ is a strong-typed language. Many conversions, specially those that imply a different interpretation of the value, require an explicit conversion. We have already seen two notations for explicit type conversion: functional and c-like casting: C+