我的ifstream方法出了什么问题

What is wrong with my ifstream method?

本文关键字：什么 问题 ifstream 方法 我的      更新时间：2023-10-16

在我的类中，我有这个ifstream方法我需要它来读取文件并在我已经创建的对象中写入信息代码有问题首先，在a.engiene值之前插入一个空格-"汽油"

当第二个对象和第三个对象被赋予值时，该方法不会为每个属性分配正确的值。

 friend ifstream& operator>>(ifstream& in, Auto &a)
        {
            char temp[31];
            temp[0] = '';
            in.getline(temp, 30, ':');
            if (temp[0])
            {
                in.getline(temp, 30, ':');
                delete[]a.engine;
                a.engine = new char[strlen(temp) + 1];
                strcpy(a.engine, temp);
                in.getline(temp, 30, ':');
                a.max_speed = atoi(temp);
                in.getline(temp, 30, ':');
                a.engine_cc = atoi(temp);
                in.getline(temp, 30, ':');
                a.avg_consumption_urban = atoi(temp);
                in.getline(temp, 30, ':');
                a.avg_speed_urban = atoi(temp);
                in.getline(temp, 30, ':');
                a.avg_consumption = atoi(temp);
                in.getline(temp, 30, ':');
                a.avg_speed = atoi(temp);
                return in;
            }
            else return in;

这就是我主要如何调用方法：

        ifstream f1("autoc.txt", ios_base::in);
                f1 >> auto1 >> auto2 >> auto3;

这是文件数据：

    auto1
    engine: gasoline
    max_speed: 250
    engine_cc: 1980
    avg_consumption_urban: 11
    avg_speed_urban: 50
    avg_consumption: 8
    avg_speed: 100
    auto2
    engine: diesel
    max_speed: 230
    engine_cc: 1600
    avg_consumption_urban: 9
    avg_speed_urban: 50
    avg_consumption: 6
    avg_speed: 80
    auto3
    engine: hybrid
    max_speed: 190
    engine_cc: 1450
    avg_consumption_urban: 7
    avg_speed_urban: 50
    avg_consumption: 4
    avg_speed: 90

这是输出窗口：https://i.stack.imgur.com/OwuZz.jpg

这不是我另一个问题的重复。我有一个几乎可以工作的代码。我需要让它为每个对象的属性指定正确的值。

in.getline(temp, 30, ':');

读取到作为属性名称的:。你还想提取之后的值，所以你需要添加

in.getline(temp, 30);

每次之后

in.getline(temp, 30, ':');

但请记住，您的程序完全忽略属性名称，只按值的顺序执行。我希望这能一劳永逸地解决你的问题。

我害怕添加一个更简洁的版本（你可能会再次询问），所以我只会提到它（就像我在回答你最初的问题时所做的那样）。它是关于使用std::string temp;和std::getline而不是std::istream::getline。

我相信您可以将大部分解析委托给STL本身。你的"autos"的格式似乎是固定的，并且有一个固定的顺序，这大大简化了解析方法（你是否坚持使用"char[31]"还不清楚，但如果你不坚持，你显然会更好地使用std:：string，就像我添加到Auto struct的"name"字段一样）

工作样本：

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

struct SeparatorReader: std::ctype<char>
{
    template<typename T>
    SeparatorReader(T &&seps):
        std::ctype<char>(get_table(seps), true) {}
    template<typename T>
    std::ctype_base::mask const *get_table(T &&seps) {
        auto rc = new std::ctype_base::mask[std::ctype<char>::table_size]();
        for(auto &sep: seps)
            rc[static_cast<unsigned char>(sep)] = std::ctype_base::space;
        return &rc[0];
    }
};

struct Auto
{
    std::string name;
    char engine[31];
    int max_speed;
    int engine_cc;
    int avg_consumption_urban;
    int avg_speed_urban;
    int avg_consumption;
    int avg_speed;
    Auto(const std::string &name) : name(name) {}
    friend std::istream &operator >>(std::istream &is, Auto &a);
    friend std::ostream &operator <<(std::ostream &os, const Auto &a);
};
std::istream &operator >>(std::istream &is, Auto &a)
{
    char tmp[31] = "";
    is >> tmp; is >> a.engine; // skip field name, read value
    is >> tmp; is >> a.max_speed;
    is >> tmp; is >> a.engine_cc;
    is >> tmp; is >> a.avg_consumption_urban;
    is >> tmp; is >> a.avg_speed_urban;
    is >> tmp; is >> a.avg_consumption;
    is >> tmp; is >> a.avg_speed;
    return is;
}
std::ostream &operator <<(std::ostream &os, const Auto &a)
{
    os << a.name << std::endl;
    os << "engine: " << a.engine << std::endl;
    os << "max_speed: " << a.max_speed << std::endl;
    os << "engine_cc: " << a.engine_cc << std::endl;
    os << "avg_consumption_urban: " << a.avg_consumption_urban << std::endl;
    os << "avg_speed_urban: " << a.avg_speed_urban << std::endl;
    os << "avg_consumption: " << a.avg_consumption << std::endl;
    os << "avg_speed: " << a.avg_speed << std::endl;
    return os;
}
int
main(int argc, char *argv[])
{
    std::ifstream stream(argv[1]);
    stream.imbue(std::locale(stream.getloc(), new SeparatorReader(" :n")));
    std::string name;
    while(stream >> name) {
        Auto a(name);
        stream >> a;
        std::cout << "------------------------------" << std::endl;
        std::cout << a;
    }
}

如果我们传递带有您的示例输入的示例文件。。。输出为：

------------------------------
auto1
engine: gasoline
max_speed: 250
engine_cc: 1980
avg_consumption_urban: 11
avg_speed_urban: 50
avg_consumption: 8
avg_speed: 100
------------------------------
auto2
engine: diesel
max_speed: 230
engine_cc: 1600
avg_consumption_urban: 9
avg_speed_urban: 50
avg_consumption: 6
avg_speed: 80
------------------------------
auto3
engine: hybrid
max_speed: 190
engine_cc: 1450
avg_consumption_urban: 7
avg_speed_urban: 50
avg_consumption: 4
avg_speed: 90
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