初学者的问题 [英] Beginner's question

问题描述

这两种写作方式有什么区别：


myClass a;

a = b;


和

myClass a = b;

我错误地认为它们是相同的（MSVC6）。


提前谢谢。


Pierre Couderc

解决方案

> myClass a;

a = b;


第一个staement将通过调用myClass的

默认构造函数来执行默认的iniitalization。第二个语句将调用myClass的

赋值运算符。

myClass a = b;


这将执行复制初始化。复制初始化意味着在必要时首次调用

用户定义的转换后，使用复制构造函数初始化

对象。

谢谢你推荐。

Pierre Couderc

Srini

Pierre Couderc写道：

这两种写作方式有什么区别：

myClass a;
a = b;


a是默认构造的，然后赋值运算符用于

将b分配给a。

和
myClass a = b;


这是初始化，而不是分配。这与以下内容完全相同：


myClass a（b）; //如果b与

相同或者：


myClass a（myClass（b））; //如果b是不同类型的


在任何一种情况下，都会调用复制构造函数和可能的另一个构造函数

，并且不使用赋值运算符。 />
我错误地认为它们是相同的（MSVC6）。

提前谢谢。

Pierre Couderc

What is the difference between these 2 ways of writing :

myClass a;
a=b;

and
myClass a=b;
I wrongly thought they were identical (MSVC6).

Thank you in advance.

Pierre Couderc

解决方案

> myClass a;

a=b;

The first staement would perform default iniitalization by calling the
default constructor of myClass. The second statement would call the
assignment operator of myClass.
myClass a=b;
This would perform copy initialization. Copy initialization means the
object is initialized using the copy constructor, after first calling a
user-defined conversion if necessary.
Thank you in advance.

Pierre Couderc

Srini

Pierre Couderc wrote:

What is the difference between these 2 ways of writing :

myClass a;
a=b;

a is default constructed first, then the assignment operator is used to
assign b to a.
and
myClass a=b;
This is initialization, not assignment. This is identical to:

myClass a(b); // if b is the same type as a

or:

myClass a(myClass(b)); // if b is of different type

In either case, the copy constructor and possibly another constructor
are called and no assignment operator is used.
I wrongly thought they were identical (MSVC6).

Thank you in advance.

Pierre Couderc

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