如何使用std :: log作为功能？

Question

我尝试将std :: log作为函数参数传递,但似乎有std :: log的重载实现,并且编译器无法解析它.代码:

#include <cmath>
#include <iostream>
#include <vector>
#include <string>
#include <functional>

template <typename FOper>
double Eval(FOper fOper, double X)
{
    return fOper(X);
}

int main(int argc, char* argv[])
{
    std::function<double(double)> fPlus1 = std::bind(std::plus<double>(), 1.0, std::placeholders::_1);
    std::cout<<Eval(fPlus1, 10.0)<<std::endl;
    //  how to write this fLog ?
    //std::function<double(double)> fLog = std::log;
    //std::function<double(double)> fLog = std::log<double>;
    std::cout<<Eval(fLog, 10.0)<<std::endl;
    return 0;
}

如果我取消注释fLog定义的任一行,则编译器会提示错误消息:

error: conversion from '<unresolved overloaded function type>' to non-scalar type 'std::function<double(doubl
e)>' requested

Answer 1

最简单的方法是简单地投射它:

typedef double (*log_d)(double);
std::function<double(double)> fLog = static_cast<log_d>(std::log);

使用强制转换,您可以向编译器提供使用重载函数的上下文,因此将从中获取正确的函数指针.