explicit 修饰只有一个参数的构造函数，以防止从参数类型到目标类类型的隐式转换。
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// stdmove.cpp -- using std::move()
#include <iostream>
#include <utility>
using
std::cout;
using
std::endl;
// use the following for g++4.5
// #define nullptr 0
// interface
class
Useless
{
private
:
int
n;
// number of elements
char
* pc;
// pointer to data
static
int
ct;
// number of objects
public
:
Useless();
explicit
Useless(
int
k);
Useless(
int
k,
char
ch);
Useless(
const
Useless & f);
// regular copy constructor
~Useless();
Useless & operator=(
const
Useless & f);
// copy assignment
void
ShowObject()
const
;
};
// implementation
int
Useless::ct = 0;
Useless::Useless()
{
cout <<
"enter "
<< __func__ <<
"()\n"
;
++ct;
n = 0;
pc = nullptr;
ShowObject();
cout <<
"leave "
<< __func__ <<
"()\n"
;
}
Useless::Useless(
int
k) : n(k)
{
cout <<
"enter "
<< __func__ <<
"(k)\n"
;
++ct;
pc =
new
char
[n];
ShowObject();
cout <<
"leave "
<< __func__ <<
"(k)\n"
;
}
Useless::Useless(
int
k,
char
ch) : n(k)
{
cout <<
"enter "
<< __func__ <<
"(k, ch)\n"
;
++ct;
pc =
new
char
[n];
for
(
int
i = 0; i < n; i++)
pc[i] = ch;
ShowObject();
cout <<
"leave "
<< __func__ <<
"(k, ch)\n"
;
}
Useless::Useless(
const
Useless & f): n(f.n)
{
cout <<
"enter "
<< __func__ <<
"(const &)\n"
;
++ct;
pc =
new
char
[n];
for
(
int
i = 0; i < n; i++)
pc[i] = f.pc[i];
ShowObject();
cout <<
"leave "
<< __func__ <<
"(const &)\n"
;
}
Useless::~Useless()
{
cout <<
"enter "
<< __func__ <<
"()\n"
;
ShowObject();
--ct;
delete
[] pc;
cout <<
"leave "
<< __func__ <<
"()\n"
;
}
Useless & Useless::operator=(
const
Useless & f)
// copy assignment
{
cout <<
"enter "
<< __func__ <<
"(const &)\n"
;
ShowObject();
f.ShowObject();
if
(
this
== &f)
return
*
this
;
delete
[] pc;
n = f.n;
pc =
new
char
[n];
for
(
int
i = 0; i < n; i++)
pc[i] = f.pc[i];
ShowObject();
cout <<
"leave "
<< __func__ <<
"(const &)\n"
;
return
*
this
;
}
void
Useless::ShowObject()
const
{
cout <<
"\t this="
<<
this
<<
", ct="
<< ct;
cout <<
", pc=("
<< n <<
", "
<< (
void
*)pc <<
", "
;
if
(n == 0)
cout <<
"(object empty)"
;
else
for
(
int
i = 0; i < n; i++)
cout << pc[i];
cout <<
" )."
<< endl;
}
int
main()
{
Useless obj1(10);
Useless obj2=5;
}
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说明：
//显式调用构造函数 ”explicit Useless(int k);”
Useless obj1(10);
//隐式调用构造函数 ”explicit Useless(int k);”。由于有explicit修饰，发生编译错误。
//error: conversion from ‘int’ to non-scalar type ‘Useless’ requested
//Useless obj2=5;
本文转自FrankNie0101 51CTO博客，原文链接：http://blog.51cto.com/frankniefaquan/1934789，如需转载请自行联系原作者
