在非成员函数中无效使用“this" [英] Invalid use of 'this' in non-member function

问题描述

我曾在一个班级工作，并开始在同一个 .cpp 文件中编写所有内容.然而，过了一会儿，我看到这个类越来越大，所以我决定把它分成一个 .h 和一个 .cpp 文件.

I had working on a class and started writing everything in the same .cpp file. However, after a while I could see the class getting bigger and bigger so I decided to split it into a .h and a .cpp file.

gaussian.h 文件:

gaussian.h file:

class Gaussian{
    private:
        double mean;
        double standardDeviation;
        double variance;
        double precision;
        double precisionMean;
    public:
        Gaussian(double, double);
        ~Gaussian();
        double normalizationConstant(double);
        Gaussian fromPrecisionMean(double, double);
        Gaussian operator * (Gaussian);
        double absoluteDifference (Gaussian);
};

gaussian.cpp 文件:

gaussian.cpp file:

#include "gaussian.h"
#include <math.h>
#include "constants.h"
#include <stdlib.h>
#include <iostream>

Gaussian::Gaussian(double mean, double standardDeviation){
    this->mean = mean;
    this->standardDeviation = standardDeviation;
    this->variance = sqrt(standardDeviation);
    this->precision = 1.0/variance;
    this->precisionMean = precision*mean;
} 

//Code for the rest of the functions...

double absoluteDifference (Gaussian aux){
    double absolute = abs(this->precisionMean - aux.precisionMean);
    double square = abs(this->precision - aux.precision);
    if (absolute > square)
        return absolute;
    else
        return square;
}

但是，我无法编译它.我试着跑步:

However, I can't get this to compile. I try running:

g++ -I. -c -w gaussian.cpp

但我明白了:

gaussian.cpp: In function ‘double absoluteDifference(Gaussian)’:
gaussian.cpp:37:27: error: invalid use of ‘this’ in non-member function
gaussian.h:7:16: error: ‘double Gaussian::precisionMean’ is private
gaussian.cpp:37:53: error: within this context
gaussian.cpp:38:25: error: invalid use of ‘this’ in non-member function
gaussian.h:6:16: error: ‘double Gaussian::precision’ is private
gaussian.cpp:38:47: error: within this context

为什么我不能用这个??我在 fromPrecisionMean 函数中使用它并编译.是因为那个函数返回一个高斯函数吗?任何额外的解释将不胜感激，我正在努力学习尽可能多的知识！谢谢！

Why can't I use this?? I am using it in the fromPrecisionMean function and that compiles. Is it because that function returns a Gaussian? Any extra explanation will be really appreciated, I am trying to learn as much as I can! Thanks!

推荐答案

您忘记将 absoluteDifference 声明为 Gaussian 类的一部分.

You forgot to declare absoluteDifference as part of the Gaussian class.

变化:

double absoluteDifference (Gaussian aux){

为此:

double Gaussian::absoluteDifference (Gaussian aux){

<小时>

旁注:通过引用而不是通过值传递可能更好:

---

Side Note: It might be better to pass by reference rather than by value:

double Gaussian::absoluteDifference (const Gaussian &aux){

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