C++编译错误：call to deleted constructor of std::istream

call to deleted constructor of ‘std::istream’ (aka ‘basic_istream’)

示例代码

#include
using namespace std;int main()
{std::istream is = cin; //出错代码return 0;
}

编译代码详细错误如下(g++ main.cpp --std=c++11 -o main)：

In file included from /usr/include/c++/5/iostream:40:0,from main.cpp:8:
/usr/include/c++/5/istream: In function ‘int main()’:
/usr/include/c++/5/istream:611:7: error: ‘std::basic_istream<_CharT, _Traits>::basic_istream(const std::basic_istream<_CharT, _Traits>&) [with _CharT = char; _Traits = std::char_traits]’ is protectedbasic_istream(const basic_istream&) = delete;^
main.cpp:27:23: error: within this contextstd::istream is = cin;^
main.cpp:27:23: error: use of deleted function ‘std::basic_istream<_CharT, _Traits>::basic_istream(const std::basic_istream<_CharT, _Traits>&) [with _CharT = char; _Traits = std::char_traits]’
In file included from /usr/include/c++/5/iostream:40:0,from main.cpp:8:
/usr/include/c++/5/istream:611:7: note: declared herebasic_istream(const basic_istream&) = delete;

分析：

1. 对象赋值时是调用拷贝构造函数进行赋值的

#include
using namespace std;class Demo {
public:Demo(int i) {number = i;cout << "Demo constructor" << endl;}Demo(const Demo &demo) {number = demo.number;cout << "copy constructor" << endl;}int geti(){return number;}
private:int number;
};int main() {Demo d(1);Demo d2 = d;cout << d2.geti() << endl;return 0;
}

输出结果：

Demo constructor
copy contuctor
1

所以出错代码std::istream is = cin; 隐藏调用了istream的拷贝函数。
2. istream的拷贝函数
由于istream的拷贝函数是protected（只能给子类调用），无法调用，所以出错。

解决：
针对这种问题，可使用下面代码替换,使用引用来达到效果。

std::istream& is = cin;

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