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#include<iostream>
using
std::cout;
using
std::endl;
template
<
typename
T>
void
swap(T&a, T&b){
a = a ^ b;
b = a ^ b;
a = a ^ b;
}
int
main(){
short
s = 50;
//error: invalid initialization of reference of type ‘int&’ from expression of type ‘short int’
//无效的初始化：用'short int'类型的表达式来初始化'int&'类型的引用。
//原因：用左值来初始化引用时，类型必须一致，不允许隐式转换。
//int &ri1 = s;
//invalid initialization of non-const reference of type ‘int&’ from an rvalue of type ‘int’
//无效的初始化：用'int'类型的右值来初始化'int &'类型的non-const引用。
//原因：用右值来初始化引用时，会产生一个同类型的匿名临时变量，对表达式的值进行隐式转换，再对这个临时变量赋值。
//int &ri2 = 50;
//如果允许对这个临时变量定义一个non-const类型的引用，那么后续代码对这个引用的写操作毫无意义。例如:
//int &i = 3;
//int& j = 4;
//swap<int>(i,j);
//将无法对i,j进行交换。
//有效的初始化：用'int'类型的右值来初始化'int &'类型的const引用。
const
int
&ri3 = 60;
}
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下面的代码显示，用右值初始化一个引用时，生成了一个匿名临时变量：
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#include<iostream>
using
std::cout;
using
std::endl;
class
TestType{
int
m_data;
public
:
TestType() : m_data(0) {
cout << __FUNCTION__ <<
"(), this = "
<<
this
;
cout <<
", m_data = ("
<< &m_data <<
", "
<< m_data <<
")\n"
;
}
//TestType(int val) : m_data(val) {
// cout << __FUNCTION__ << "(int val), this = " << this;
// cout << ", m_data = (" << &m_data << ", " << m_data << ")";
// cout << ", val = (" << &val << ", " << val << ").\n";
//}
TestType(
const
int
&rv) : m_data(rv) {
cout << __FUNCTION__ <<
"(int &rv), this = "
<<
this
;
cout <<
", m_data = ("
<< &m_data <<
", "
<< m_data <<
")"
;
cout <<
", rv = ("
<< &rv <<
", "
<< rv <<
").\n"
;
}
};
int
main(){
cout <<
"sizeof(TestType) = "
<<
sizeof
(TestType) << endl;
TestType dat1;
TestType dat2(100);
int
i = 200;
cout <<
"i = ("
<< &i <<
", "
<< i <<
")\n"
;
TestType dat3(i);
return
0;
}
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运行结果：
sizeof(TestType) = 4
TestType(), this = 0x7fffc5b81cd0, m_data = (0x7fffc5b81cd0, 0)
TestType(int &rv), this = 0x7fffc5b81ce0, m_data = (0x7fffc5b81ce0, 100), rv = (0x7fffc5b81cfc, 100).
i = (0x7fffc5b81cfc, 200)
TestType(int &rv), this = 0x7fffc5b81cf0, m_data = (0x7fffc5b81cf0, 200), rv = (0x7fffc5b81cfc, 200).
本文转自FrankNie0101 51CTO博客，原文链接：http://blog.51cto.com/frankniefaquan/1934509，如需转载请自行联系原作者
