C++读取文件到Cust对象异常及多行读取方法咨询

Hey there! Let's work through the problems you're facing with reading file data into your Cust objects, and then cover how to handle multi-line content too.

First: Fixing the Single-Line Read & File Emptying Issues #

Your output anomalies (missing name, wrong boolean mapping, garbage numbers) and unexpected file emptying are likely from a few common mistakes—let's break them down and fix them:

1. Stop Accidentally Emptying Your File #

If your code was using ofstream instead of ifstream to open the file, or added flags like ios::trunc (which truncates/clears the file), that's why your file content vanished. Always use ifstream for reading—it defaults to ios::in mode, which only reads the file without modifying it.

2. Handle "true"/"false" Strings for Boolean Values #

C++'s ifstream doesn't natively read string values like "true" into a bool variable (it expects 0/1 instead). Trying to do this breaks the read sequence, leading to garbage values for subsequent variables. Instead:

• Read the boolean value as a string first
• Convert it to a bool manually by checking if the string equals "true"

3. Correct Read Sequence & Variable Types #

Make sure your read order exactly matches the file's field order: name → robber string → time → items, and that each variable's type matches what you're reading.

Working Single-Line Read Code Example

#include <fstream>
#include <string>
#include <iostream>

using namespace std;

class Cust {
private:
    string m_name;
    bool m_robber;
    int m_time;
    int m_items;
public:
    Cust(string name, bool robber, int time, int items) 
        : m_name(name), m_robber(robber), m_time(time), m_items(items) {}
    
    void print() {
        cout << (m_robber ? "robber" : "shopper") << " " << m_name << " " << m_time << " " << m_items << endl;
    }
};

int main() {
    // Use ifstream for reading—no extra flags needed
    ifstream inFile("your_file.txt");
    if (!inFile.is_open()) {
        cerr << "Error: Couldn't open the file!" << endl;
        return 1;
    }

    string name;
    string robberStr; // Capture "true"/"false" as string first
    int time, items;

    // Read the four fields in order
    inFile >> name >> robberStr >> time >> items;

    // Convert string to bool
    bool isRobber = (robberStr == "true");

    Cust cust(name, isRobber, time, items);
    cust.print();

    inFile.close();
    return 0;
}

Reading Multiple Lines of Data #

To process multiple lines (like your example: Robbie true 1 2 and Shaun false 3 4), you can use a loop that runs until the stream reaches the end of the file. The while loop will automatically exit when inFile can't read any more data (e.g., end of file).

Multi-Line Read Code Example

int main() {
    ifstream inFile("your_file.txt");
    if (!inFile.is_open()) {
        cerr << "Error: Couldn't open the file!" << endl;
        return 1;
    }

    string name;
    string robberStr;
    int time, items;

    // Loop until no more data can be read
    while (inFile >> name >> robberStr >> time >> items) {
        bool isRobber = (robberStr == "true");
        Cust cust(name, isRobber, time, items);
        cust.print();
    }

    inFile.close();
    return 0;
}

Quick Final Tips #

• Always check if the file opened successfully with !inFile.is_open()—this saves you from debugging silent failures
• If your file has lines with whitespace in the name (e.g., "Robbie the Robber"), you'll need to adjust reading logic (use getline with a delimiter), but your current format (single-word names) works fine with >>
• Avoid using using namespace std; in large projects, but it's okay for small test code like this

内容的提问来源于stack exchange，提问作者Zevvysan