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// interfaceclass 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;
};// implementationint 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;
} |
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