## Why is my temperature value being stored in the array instead of the intended variable in my C class?-C++-php.cn

## Why is my temperature value being stored in the array instead of the intended variable in my C class?

Barbara Streisand

Release： 2024-10-25 00:27:30

Original

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## Why is my temperature value being stored in the array instead of the intended variable in my C class?

Shadowing Variables in C

In object-oriented programming, shadowing occurs when a variable defined within a class has the same name as a variable in an outer scope. This can lead to unexpected behavior, as the inner variable takes precedence over the outer variable.

Problem: Shadowing in a Class

Consider the following class definition:

<code class="cpp">class Measure {
    int N;
    double measure_set[];
    char nomefile[];
    double T;

    public:
    void get( );
    void printall( );
    double mean( );
    double thermal_comp( );
};</code>

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The get method in this class is intended to read values from a file and save them in the measure_set array, and to read a temperature value and store it in the T variable.

However, when you implement the get method as follows:

<code class="cpp">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;
}</code>

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You noticed that the temperature value (T) is being stored in the first element of the measure_set array (measure_set[0]) instead of the intended T variable.

Solution

This occurs because C allows variables with the same name to be declared in different scopes. In this case, the T variable declared in the get method shadows the class member variable T.

To avoid shadowing, you can either use different names for the variables or use the scope resolution operator (::) to explicitly refer to the class member variable.

Using a different name for the temperature variable in the get method would look like this:

<code class="cpp">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;
    double temperature;  // Use a different name for the temperature variable
    cin >> temperature;
    T = temperature;
    cout << endl;
}</code>

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Using the scope resolution operator to explicitly refer to the class member variable would look like this:

<code class="cpp">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 >> this->T;  // Use the scope resolution operator to refer to the class member variable
    cout << endl;
}</code>

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