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如题
#include <iostream>
#include <functional>
using namespace std;
void g(ostream &os)
{
os << "1";
}
int main()
{
//非法
auto f = bind(g, &cout);
f();
//合法
auto h = bind(g, ref(cout));
h();
return 0;
}
天蓬老师2017-04-17 14:26:58
因为函数原型就是这样规定的,你写成&cout
就是个指针了,当然非法;用std::ref
包裹一下就符合原型要求了,相当于传个引用进去,同样还有不可变的std::cref
,下面是官方对于参数类型的要求:
fn
A function object, pointer to function or pointer to member.
Fn shall have a decay type which is move-constructible from fn.
args...
List of arguments to bind: either values, or placeholders.
The types in Args... shall have decay types which are move-constructible from their respective arguments in args....
If for any argument, its decay type is a reference_wrapper, it bounds to its referenced value instead.
你看最后一行,说要求得是个reference_wrapper
,std::ref
和std::cref
就是干这个的