c++ - 写入文件的 C++ 中双重类型的意外舍入

Question

我正在开发一个 C++ 程序，其中包含大量 double 类型的数字(数百万和数十亿的值，小数点右侧只有几位)。我正在对这些数字进行计算，然后将结果打印到文本/CSV 文件中。我注意到在文本文件中，我所有的数字似乎都四舍五入(到六位数)。因此，值 13,169,911 在我的输出文件中显示为 13,169,900。

这种四舍五入是否只发生在打印品上？为了获得变量中的全部数字，我是否只需要在写入文件时指定一些内容？我在下面包含了一个写入文件代码的示例:

void PrintPropFinance(vector<PropFinance>& PF, int NumProps, int Iterations, int ForecastLength, 
          string CurDeal, string ModelRunID, string ScenName, Assumptions& Ass) {

string filename;
ofstream OutFile;
ostringstream s1;

s1 << BASEPATH << "Output/" << CurDeal << "_" << ModelRunID << "_" << 
            ScenName << "_PropFinance" << ".csv";
filename = s1.str();

OutFile.open(filename);

// Put in the column headers first
OutFile << "PropID" << "," 
        << "Item" << ","
        << "StartDate" << ","
        << "NumOfPeriod" << ","
        << "Result" << ","
        << "Isap" << ","
        << "CurLoanBal" << ","

for (int i=1; i<=NumProps; ++i) {
    // Populate the single-vector variables
    OutFile << PF[i].PropID << "," 
            << PF[i].Item << ","
            << PF[i].StartDate << ","
            << PF[i].NumOfPeriod << ","
            << PF[i].Result << ","
            << PF[i].Isap << ","
            << PF[i].CurLoanBal << ","
                                    << endl;
}
OutFile.close();
}

// Prop finance class definition
class PropFinance {
public:
    string PropID;
    int Item;
    string StartDate;

    int NumOfPeriod;
    string Isap;
    double CurLoanBal;
}

Answer 1

问题可能与输出流为 double 产生输出的方式有关:如果 13169911 以“科学计数法”打印，它看起来像1.31699E7。 Excel 会很好地读取此符号，但会为它“看不到”的数字置零，使数字看起来像 13,169,900。

要解决此问题，请添加 fixed当您输出 double 以确保打印所有数字时的操纵器:

OutFile << PF[i].PropID << "," 
        << PF[i].Item << ","
        << PF[i].StartDate << ","
        << PF[i].NumOfPeriod << ","
        << fixed << PF[i].Result << ","
        << PF[i].Isap << ","
        << fixed << PF[i].CurLoanBal << ","
        << endl;