C++ 在非成员函数中无效使用“this”
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Invalid use of 'this' in non-member function
提问by coconut
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.
我在一个班上工作，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。
gaussian.h file:
gaussian.h 文件：
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 file:
gaussian.cpp 文件：
#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;
}
However, I can't get this to compile. I try running:
但是，我无法编译它。我尝试运行：
g++ -I. -c -w gaussian.cpp
But I get:
但我得到：
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
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!
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！
回答by Mysticial
You forgot to declare absoluteDifferenceas part of the Gaussianclass.
您忘记声明absoluteDifference为Gaussian课程的一部分。
Change:
改变：
double absoluteDifference (Gaussian aux){
to this:
对此：
double Gaussian::absoluteDifference (Gaussian aux){
Side Note:It might be better to pass by reference rather than by value:
旁注：通过引用而不是通过值传递可能更好：
double Gaussian::absoluteDifference (const Gaussian &aux){
