std::function::operator bool
STD：：功能：：操作员bool
| explicit operator bool() const; | | (since C++11) |
|---|
检查是否*this存储可调用的函数目标，即不为空。
参数
%280%29
返回值
true如果*this存储可调用函数目标，false否则。
例外
noexcept规格：
noexcept
例
二次
#include <functional>
#include <iostream>
void sampleFunction()
{
std::cout << "This is the sample function!\n";
}
void checkFunc( std::function<void()> &func )
{
// Use operator bool to determine if callable target is available.
if( func )
{
std::cout << "Function is not empty! Calling function.\n";
func(
}
else
{
std::cout << "Function is empty. Nothing to do.\n";
}
}
int main()
{
std::function<void()> f1;
std::function<void()> f2( sampleFunction
std::cout << "f1: ";
checkFunc( f1
std::cout << "f2: ";
checkFunc( f2
}
二次
产出：
二次
f1: Function is empty. Nothing to do.
f2: Function is not empty! Calling function.
This is the sample function!
二次
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