C++ 二维数组用文件中的最后一个元素值填充所有元素

Question

这就是我编写的程序。由于某种原因，它用最后一个元素值填充数组的所有元素。该程序应该只是打开并读取文件。对行求和。对列求和，然后对所有元素求和。

#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
const int NUM_TYPE = 5; // num of types of salsa
const int NUM_SALE = 4; // num of quarters per salsa

void salsaIn(float salsa[][NUM_SALE]);
void salsaType(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);
void salsaQ(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);
void totalSalsa(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);
void displayArray(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE);

int main()
{
    float salsa[NUM_TYPE][NUM_SALE];

    salsaIn(salsa);
    displayArray(salsa, NUM_TYPE, NUM_SALE);
    salsaType(salsa, NUM_TYPE, NUM_SALE);
    salsaQ(salsa, NUM_TYPE, NUM_SALE);
    totalSalsa(salsa, NUM_TYPE, NUM_SALE);

    return 0;
}
//reads the salsa.txt file
void salsaIn(float salsa[][NUM_SALE])
{
    float salsaT = 0;
    ifstream file("salsa.txt");

    if (file.is_open())
    {
        cout << "Successful. Reading data." << endl;
        while (!file.eof())
        {
            for (int i = 0; i < NUM_TYPE; i++)
            {
                for (int j = 0; j < NUM_SALE; j++)
                {

                    file >> salsaT;
                    if (salsa < 0)
                    {
                        cout << "error, value less than 0, set to 0"<<endl;
                        salsaT = 0;
                    }

                    salsa[i][j] = salsaT;
                }
            }
        }

    }
    file.close();

    return;
}
//calculates and displays sales for each salsa type
void salsaType(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    for (int row = 0; row < NUM_TYPE; row++)
    {
        float total = 0;

        for (int col = 0; col < NUM_SALE; col++)
        {
            total += salsa[row][col];
        }
        //display the total sales for each salsa type.
        cout << "total sales for salsa " << (row + 1) << " is " << total
                << endl;

        return;
    }

}
void displayArray(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    for (int row = 0; row < NUM_TYPE; row++)
    {
        float total = 0;

        for (int col = 0; col < NUM_SALE; col++)
        {
            cout << setw(5) << salsa[row][col] << endl;
        }
        //display the total sales for each salsa type.
    }

    return;
}
//calculates and displays the sales of each quarter.
void salsaQ(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    for (int col = 0; col < NUM_SALE; col++)
    {
        float totalq = 0;

        for (int row = 0; row < NUM_TYPE; row++)
            totalq += salsa[row][col];

        cout << "Sales for quarter " << (col + 1) << " is " << totalq << endl;
    }

    return;

}
//calculates and displays the sales for the company last year.
void totalSalsa(float salsa[][NUM_SALE], int NUM_TYPE, int NUM_SALE)
{
    float totalS = 0;
    for (int row = 0; row < NUM_TYPE; row++)
    {

        for (int col = 0; col < NUM_SALE; col++)

            totalS += salsa[row][col];

    }

    cout << "The total sales for the company last year is " << totalS << endl;
}

这是程序的最终输出。

Successful. Reading data.3905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.643905.64total sales for salsa 1 is 15622.6Sales for quarter 1 is 19528.2Sales for quarter 2 is 19528.2Sales for quarter 3 is 19528.2Sales for quarter 4 is 19528.2The total sales for the company last year is 78112.8

谢谢大家的帮助。我有点卡在程序的其余部分了。

Answer 1

发生了什么:

while (!file.eof())

循环直到设置 EOF 标志。在程序尝试从文件中读取值并找到文件末尾之前，不会设置此标志。通常这意味着 EOF 标志不会被设置，直到程序试图从文件中读取一个值并失败，因为没有更多的值可以读取。

{
    for (int i = 0; i < NUM_TYPE; i++)
    {
        for (int j = 0; j < NUM_SALE; j++)
        {

这些循环将尝试从文件中读取 20 个值

            file >> salsaT;

从文件中读取一个值。没有检查以确保从文件中读取了值。失败时，salsaT BEFORE C++11 中的值保持不变。在 C++11 之后它被清零了。如果您不是针对 C++11 进行编译，则会出现您重复的最后一个数字。

            if (salsa < 0) // unrelated bug here
            {
                cout << "error, value less than 0, set to 0"<<endl;
                salsaT = 0;
            }

            salsa[i][j] = salsaT;
        }
    }
}

从文件或 while (!file.eof()) 循环的每次迭代中读取 20 个值。如果文件中恰好有 20 个值，则读取所有 20 个值。可能没有设置 EOF，所以进入了 while 循环。另外 20 个值被读入同一个数组，但这次没有要读取的值。该数组很可能包含 20 次重复的最后一次成功读取的值。

解决方法:

while 循环的死亡!

for (int i = 0; i < NUM_TYPE; i++)
{
    for (int j = 0; j < NUM_SALE; j++)
    { // read 20 values from file
        if (file >> salsaT)
        { // if we got a value
            if (salsaT < 0)
            {
                cout << "error, value less than 0, set to 0"<<endl;
                salsaT = 0;
            }
        }
        else
        { // Bad or no value. try to clean up.
            if (file.eof())
            {
                cout << "File ended too soon"<<endl;
            }
            else
            {
                cout << "error, bad value in file"<<endl;
                file.clear();
                file.ignore(numeric_limits<streamsize>::max(), '\n');
            }
            salsaT = 0;
        }
        salsa[i][j] = salsaT; // store
    }
}