阴影变量 [英] Shadowing variables

问题描述

我的问题是关于变量定义到类。我告诉你我的问题。

My question is about variables defined into classes. I show you my problem.

我已经定义了这个类：

class Measure {

int N;
double measure_set[];
char nomefile[];
double T;

public:
    void get( );
    void printall( );
    double mean( );
    double thermal_comp( );
};

我想要方法get执行以下操作：

I would like method get to do the following:

1. 从.dat文件读取数字并保存到measure_set数组中;


2. 读取用户输入并将其保存到变量T中;

这是我所做的：

void Measure::get() 
{   
    cout << "Insert filename:" << endl;
    cin >> nomefile;
    cout << endl;
    cout << nomefile << endl;
    cout << endl;

    int M=0;
    int nmax=50;

    ifstream f;
    f.open(nomefile);
    while(M<nmax)
    {
        f >> measure_set[M];
        if(f.eof()) 
        break;
        M++;
    }
    f.close();
    N=M+1;

    cout << "Insert temperature:" << endl;
    cin >> T;
    cout << endl;
} 

会发生什么是我注意到T被记住在 measure_set [0] 。为什么会发生这种情况，如何写一个工作代码？我不是C ++的专家，使用这只是为了计算的目的，虽然我可以解决我的问题在其他方式我想学习如何使这工作在C + +。非常感谢！

What happens is that I've noticed that T is memorized in measure_set[0]. Why this happens and how can I write a working code? I'm not that expert in C++, using this only for computation purposes, although I could solve my problem in other ways I would like to learn how to make this work in C++. Thanks a lot!

推荐答案

在C和C ++中，同一个名称在多个范围内使用是合法的 - （例如gcc -Wshadow）会提供一个机制来警告你，因为它可能导致混乱。

In both C and C++ it is legal for the same name to be used within multiple scopes - some compilers (e.g. gcc -Wshadow) will provide a mechanism that warns you about this since it can cause confusion.

#include <iostream>

int i = 0;
int main() {
    int i = 1;
    for (int i = 0; i < 10; ++i) {
        int i = 2 * i;
        std::cout << i << std::endl;
    }
    return 0;
}

一些编译器将编译此输出'0，2，4，6， 8，...。 有些不会。

Some compilers will compile this and output '0, 2, 4, 6, 8, ...'. Some won't.

避免的常见方式这是使用前缀。 m_表示成员，s_表示静态，g_表示全局等。一些编码样式对成员变量使用_后缀。这也有助于保持成员变量不与类似命名的getters / setters冲突，如果这是你的骆驼滚动。

A common way to avoid this is to use prefixes. "m_" for "member", "s_" for "static", "g_" for "global", etc. Some coding styles use a "_" suffix for member variables. This also helps to keep member variables from clashing with similarly named getters/setters if that's the way your camel rolls.

class Measure {
    int         m_n;
    double      m_measureSet[MEASURE_SET_SIZE]; // [] is not legal in a class.
    std::string m_nomefile;
    double      m_t;

public:
    const std::string& nomefile() const { return m_nomefile; }
    ...
};

在这种情况下，在使用中，我倾向于发现开发人员使用访问器比起成员（在开头比类型m_更容易添加（））。

Where this pays off is in the usage, I tend to find developers are encouraged to use the accessors rather than the members (it seems to be easier to add () at the end than type "m_" at the beginning).

std::cout << "Measuring file " << nomefile << std::endl;

会成为

std::cout << "Measuring file " << m_nomefile << std::endl;

或更佳：

std::cout << "Measuring file " << nomefile() << std::endl;

这篇关于阴影变量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！