我的 ifstream 方法有什么问题？

Question

在我的 class 我有这个 ifstream 方法我需要它来读取文件并将信息写入我已经创建的对象代码有问题首先，a.engiene 值在值 - “gasoline”

之前插入 space

并且当给第二个对象和第三个对象赋值时，该方法没有为每个属性赋值正确。

 friend ifstream& operator>>(ifstream& in, Auto &a)
        {
            char temp[31];
            temp[0] = '[=10=]';
            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;

这是我在 main 中调用方法的方式：

        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 window： http://imgur.com/tHe49se

这与我的其他问题不重复。我有这个几乎可以工作的代码。我需要让它为每个对象的属性分配正确的值。

Answer 1

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

读取到 :，即属性个名称。您还想提取之后的值，因此您需要添加

in.getline(temp, 30);

每个

之后

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

但请记住，您的程序完全忽略了属性名称，而只是按值的顺序进行。我希望这能一劳永逸地解决你的问题。

我不敢添加一个更简洁的版本（你可能会再次询问），所以我只是提一下（就像我在你原来的问题的答案中所做的那样）。这是关于使用 std::string temp; 和 std::getline 而不是 std::istream::getline.

Answer 2

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，这大大简化了解析的方法（你是否坚持使用 "char [31]" 不清楚，但如果你不是，你显然会使用 std::string 会更好，因为我添加到 Auto 结构的 "name" 字段就是这种情况）

工作示例：

#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;
    }
}

如果我们将样本文件与您的样本输入一起传递...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

我的 ifstream 方法有什么问题？

What is wrong with my ifstream method?

c++

oop

file

ifstream