Question

在我班上我有这个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，在值“ - 汽油”

之前插入一个空格的a.engiene值

当第二个对象和第三个对象被赋值时，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] = '\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;

这就是我在main中调用方法的方法：

        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： http://imgur.com/tHe49se

这与我的其他问题不重复。我有这个代码几乎可以工作。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:，它们是属性名称。您还希望在此之后提取值，因此您需要添加

in.getline(temp, 30);

每次

后

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

但请记住，您的程序完全忽略了属性名称，只是按值的顺序排列。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（就像我在原始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

我相信你可以将大部分解析委托给STL本身。您的＆＃34; autos＆＃34;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＆＃34; char [31]＆＃34;目前还不清楚，但如果你不是你，那么很明显最好使用std :: string，因为＆＃34; name＆＃34;字段是我添加到Auto结构中的情况）

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;
    }
}

如果我们使用您的示例输入传递示例文件...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

我的ifstream方法有什么问题？

2 个答案: