显式分配vs隐式分配 [英] Explicit Assignment vs Implicit Assignment

问题描述

我正在阅读一本C ++教程，但它实际上并没有给我带来两者之间的差别（除了语法）。

您还可以在声明时为您的变量赋值。当我们
使用赋值运算符（等于
sign）给变量赋值时，它被称为显式赋值：

  int nValue = 5; //显式赋值
  

也可以使用隐式赋值赋值给变量：

  int nValue（5）; //隐式赋值
  

即使隐式赋值看起来很像函数调用，
编译器跟踪哪些名称是变量，以及哪些是
函数，以便它们可以正确解析。

？

$ p

解决方案

第一个是首选类型，如 int ;

例如，如果你定义了一个 class Foo

code>，可以从单个 int ，

构建

  Foo x（5）; 
  

优先于

  Foo x = 5; 
  

（当你使用多个参数时， $ c> Foo x = Foo（5，hello）; 这是普通的丑，看起来像 operator = 正在调用。 / p>

I'm reading a tutorial for C++ but it didn't actually give me a difference (besides syntax) between the two. Here is a quote from the tutorial.

You can also assign values to your variables upon declaration. When we assign values to a variable using the assignment operator (equals sign), it’s called an explicit assignment:

int nValue = 5; // explicit assignment

You can also assign values to variables using an implicit assignment:

int nValue(5); // implicit assignment

Even though implicit assignments look a lot like function calls, the compiler keeps track of which names are variables and which are functions so that they can be resolved properly.

Is there a difference? Is one more preferred over the other?

解决方案

The first is preferred with primitive types like int; the second with types that have a constructor, because it makes the constructor call explicit.

E.g., if you've defined a class Foo that can be constructed from a single int, then

Foo x(5);

is preferred over

Foo x = 5;

(You need the former syntax anyway when more than one argument is passed, unless you use Foo x = Foo(5, "hello"); which is plain ugly and looks like operator= is being called.)

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