Question

我正在使用视觉工作室，并且这个程序从一个名为inmpg的txt文件中获取数据，然后打印出一个名为outmpg.txt的生成文件。代码没有错误，但是当控制台窗口出现时，它只能进入“从文件读取”而不会从那里继续。 “outmpg.txt”已创建但空白。任何帮助表示赞赏。

#include <iostream> 
#include <fstream> // For file I/O 
using namespace std;
int main()
{
float amt1; // # of gallons for fillup 1 
float amt2; // # of gallons for fillup 2 
float amt3; // # of gallons for fillup 3 
float amt4; // # of gallons for fillup 4 
float startMiles; // Starting mileage 
float endMiles; // Ending mileage 
float mpg; // Computed miles per gallon 
ifstream inMPG; // Holds gallon amts & mileages. Input 
ofstream outMPG; // Holds miles per gall. Output 
                 // Open the files 
inMPG.open("inmpg.txt");
if (inMPG.fail())
{
    cout << "can't find inmpg.txt" << endl;
    return 0;
}

outMPG.open("outmpg.txt");
if (outMPG.fail())
{
    cout << "can't create/ open outmpg.txt" << endl;
    return 0;
}

// Get data (priming read) 
cout << "Reading from file" << endl;
inMPG >> amt1 >> amt2 >> amt3 >> amt4 >> startMiles >> endMiles;
while (!inMPG.eof())
{
    // Compute miles per gallon 
    mpg = (endMiles - startMiles) / (amt1 + amt2 + amt3 + amt4);
    // Output results 
    cout << "wrote to file outmpg.txt" << endl;
    outMPG << "For the gallon amounts" << endl;
    outMPG << amt1 << ' ' << amt2 << ' ' << amt3 << ' ' << amt4 << endl;
    outMPG << "and a starting mileage of " << startMiles << endl;
    outMPG << "and an ending mileage of " << endMiles << endl;
    outMPG << "the mileage per gallon is " << mpg << endl;
    cout << "\n Reading the next set of data" << endl;
    inMPG >> amt1 >> amt2 >> amt3 >> amt4 >> startMiles >> endMiles;
}
return 0;

}

Answer 1

问题来自于您第一次从inMPG文件开始阅读时。如果您只有一个条目，则循环永远不会执行，并且会跳过它，因为它已经到达文件的末尾。因此，永远不要写入outMPG文件。

我所做的是删除while循环上方的两行，并将它们放在while循环内部的开头，并删除循环内的最后两行。

另一个问题是.eof（）调用。至于为什么它在这种情况下实际上不起作用超出了我，但我使用了.peek（）。所以语句可以改为while（inMPG.peek（）！= EOF）。

这是为我工作的代码片段

#include <iostream>
#include <fstream> // For file I/O
using namespace std;
int main()
{
    float amt1; // # of gallons for fillup 1
    float amt2; // # of gallons for fillup 2
    float amt3; // # of gallons for fillup 3
    float amt4; // # of gallons for fillup 4
    float startMiles; // Starting mileage
    float endMiles; // Ending mileage
    float mpg; // Computed miles per gallon
    ifstream inMPG; // Holds gallon amts & mileages. Input
    ofstream outMPG; // Holds miles per gall. Output
    // Open the files
    inMPG.open("inmpg.txt");
    if (inMPG.fail())
    {
        cout << "can't find inmpg.txt" << endl;
        return 0;
    }

    outMPG.open("outmpg.txt");
    if (outMPG.fail())
    {
        cout << "can't create/ open outmpg.txt" << endl;
        return 0;
    }

    while(inMPG.peek() != EOF)
    {
        cout << "Reading the next set of data" << endl;
        inMPG >> amt1 >> amt2 >> amt3 >> amt4 >> startMiles >> endMiles;
        // Compute miles per gallon
        mpg = (endMiles - startMiles) / (amt1 + amt2 + amt3 + amt4);
        // Output results
        cout << "wrote to file outmpg.txt" << endl;
        outMPG << "For the gallon amounts" << endl;
        outMPG << amt1 << ' ' << amt2 << ' ' << amt3 << ' ' << amt4 << endl;
        outMPG << "and a starting mileage of " << startMiles << endl;
        outMPG << "and an ending mileage of " << endMiles << endl;
        outMPG << "the mileage per gallon is " << mpg << endl;

    }
    return 0;
}

我的输入文件是这个;

24.0 25.0 23.0 20.0 30.0 50.0

无法找到解决方案

1 个答案: