C++中ifstream读取数据写入ofstream失败问题排查

我正在做一个项目，需要打开文件、处理数据、识别特定特征并筛选对应行。程序运行时控制台输出的结果是正确的，但尝试把这些数据写入指定的ofstream文件时，文件里完全没有内容。以下是我的代码：

#include <fstream>
#include <iomanip>
#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

int main() {
    string fileName;
    ifstream iFile;
    iFile.open(fileName);
    // keep asking the user for file name again and again till the file opens successfully
    while(1){
    cout<<"Open File: ";
    cin>>fileName;
    iFile.open(fileName);//open file
        if(!iFile){
            cout << "Could not open " << fileName << endl;
        }else//valid file name,exit the loop
            break;
        }
    string plate;
    string date;
    string time;
    string weight;
    string speed;
    int foundWeight = 0;
    int foundSpeed = 0;
    int count = 0;
    vector<string> v1;
    vector<string> v2;
    ofstream outFile("[10-09-2022] Report.txt:", ios::app);

    while (getline(iFile, plate, ',')) {
    getline(iFile, date, ',') ;
    getline(iFile, time, ',') ;
    getline(iFile, weight, ',');
    foundWeight = stoi(weight);
    getline(iFile, speed);
    foundSpeed = stoi(speed);
        if(foundWeight < 5000 && foundSpeed > 45){
            cout << "[" << time << "]" << ' ' << plate << endl;
            outFile << "[" << time << "]" << ' ' << plate << endl;
            count++;
        }else if(foundWeight >= 5000 && foundSpeed > 30){
            cout << "[" << time << "]" << ' ' << plate << endl;
            outFile << "[" << time << "]" << ' ' << plate << endl;
            count++;
        }
    }

    cout << count << " violations logged.\n";
    outFile << count;
    outFile.close();

    return 0;   
}

程序运行输出：

Open File: a5_short.dat
[06:11] MVE-717
[06:23] OLC-651
[06:28] KQJ-359
[06:37] NFT-062
[06:41] MCW-399
[06:45] BWQ-255
[06:49] ZKL-544
[07:00] FHQ-348
[07:11] QME-845
[07:13] OWG-325
[07:34] NNJ-571
[07:43] ZKI-228
12 violations logged.

显示的数值都是正确的，但就是无法写入到"[10-09-2022] Report.txt:"文件里。

修复方案 #

1. 修正输出文件名
   输出文件名末尾的冒号:是非法字符（Windows等系统不允许文件名包含冒号），导致文件无法创建或写入。将文件名改为"[10-09-2022] Report.txt"。

2. 检查输出文件是否成功打开
   和输入文件的处理逻辑一致，添加对outFile的状态检查，避免因权限、路径错误等问题导致写入失败。

3. 移除多余的输入文件打开操作
   代码开头的iFile.open(fileName);执行时fileName是空字符串，会破坏输入流的状态，导致后续读取异常，直接删除这行代码。

4. 补充完整的文件输出内容
   控制台输出了完整的统计信息，但文件只写入了数字count，建议保持输出内容一致，提升报告可读性。

修复后的完整代码：

#include <fstream>
#include <iomanip>
#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

int main() {
    string fileName;
    ifstream iFile;

    // 循环请求文件名直到成功打开
    while(true){
        cout << "Open File: ";
        cin >> fileName;
        iFile.open(fileName);
        if(!iFile){
            cout << "Could not open " << fileName << endl;
        }else{
            break;
        }
    }

    string plate;
    string date;
    string time;
    string weight;
    string speed;
    int foundWeight = 0;
    int foundSpeed = 0;
    int count = 0;
    vector<string> v1;
    vector<string> v2;

    // 修正输出文件名，去掉非法的冒号
    ofstream outFile("[10-09-2022] Report.txt", ios::app);
    // 检查输出文件是否成功打开
    if(!outFile){
        cout << "Could not open output file!" << endl;
        return 1;
    }

    while (getline(iFile, plate, ',')) {
        getline(iFile, date, ',') ;
        getline(iFile, time, ',') ;
        getline(iFile, weight, ',');
        foundWeight = stoi(weight);
        getline(iFile, speed);
        foundSpeed = stoi(speed);

        if(foundWeight < 5000 && foundSpeed > 45){
            cout << "[" << time << "]" << ' ' << plate << endl;
            outFile << "[" << time << "]" << ' ' << plate << endl;
            count++;
        }else if(foundWeight >= 5000 && foundSpeed > 30){
            cout << "[" << time << "]" << ' ' << plate << endl;
            outFile << "[" << time << "]" << ' ' << plate << endl;
            count++;
        }
    }

    string logMsg = to_string(count) + " violations logged.";
    cout << logMsg << endl;
    outFile << logMsg << endl;

    // 关闭文件流
    outFile.close();
    iFile.close();

    return 0;   
}

内容的提问来源于stack exchange，提问作者annon101