从C++文件中读取不同类型的数字数据

我想这对你来说太过分了。

仍然想向公众展示，如果您使用知道如何投影到 AST 数据类型的分析器生成器，代码会变得多么优雅。下面是一个 Spirit 示例，它会自动处理所有转换为line_rec所在的vector<line_rec>：

struct line_record {
    int   a;
    float b, c, d;
    int   e;
    // column f is rest.size()
    std::vector<std::pair<int, float> > rest;
};    

法典

住在科里鲁

#include <boost/fusion/include/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
struct line_record {
    int   a;
    float b, c, d;
    int   e;
    // column f is rest.size()
    std::vector<std::pair<int, float> > rest;
};    
BOOST_FUSION_ADAPT_STRUCT(line_record, a, b, c, d, e/*, f*/, rest)

// define a Spirit Grammar
using Iterator = boost::spirit::istream_iterator;
namespace parser {
    static auto const line = [] {
        using namespace boost::spirit::qi;
        _a_type number_of_pairs;
        rule<Iterator, line_record(), locals<unsigned> > line_parser;
        return line_parser %= skip(blank) [
                    int_ >> float_ >> float_ >> float_ >> 
                    int_ >> omit[ uint_ [ number_of_pairs = _1 ] ] >> 
                    repeat(number_of_pairs) [ int_ >> float_ ] >>
                    (eol|eoi)
                ];
    }();
}
#include <fstream>
int main() {
    using namespace std;
    ifstream ifs("input.txt");
    Iterator first(ifs >> noskipws), last;
    vector<line_record> all_data;
    if (parse(first, last, *parser::line, all_data))
    {
        cout << "Parsed " << all_data.size() << " linesn";
        for (auto& rec : all_data) {
            cout << rec.a << "t"
                 << rec.b << "t" << rec.c << "t" << rec.d << "t"
                 << rec.e << "t"
                 << rec.rest.size();
            for (auto& trailing : rec.rest)
                cout << "t(" << trailing.first << ", " << trailing.second << ")";
            cout << "n";
        }
    } else {
        cout << "Parse failedn";
    }
    if (first != last) {
        cout << "Remaining input: '" << string(first, last) << "'n";
    }
}

输出

鉴于您的问题输入：

Parsed 13 lines
1   436.514 0.587   8.318   1   3   (8, 0.929)  (7, 0.972)  (2, 1.44)
2   436.004 0.744   7.02    1   3   (10, 1.117) (9, 1.155)  (1, 1.44)
3   436.263 0.603   5.029   2   1   (9, 0.916)
4   437.966 0.594   6.086   2   1   (9, 0.835)
5   434.577 1.454   5.82    2   1   (10, 0.898)
6   433.99  1.139   7.596   2   1   (10, 0.919)
7   437.917 0.102   8.485   4   3   (1, 0.972)  (11, 1.503) (12, 1.428)
8   435.617 0.849   9.51    4   3   (13, 1.463) (1, 0.929)  (14, 1.49)
9   436.839 0.691   5.88    4   3   (4, 0.835)  (3, 0.916)  (2, 1.155)
10  434.623 1.036   6.798   4   3   (6, 0.919)  (5, 0.898)  (2, 1.117)
11  438.321 39.569  9.683   3   1   (7, 1.503)
12  438.614 39.463  7.42    3   1   (7, 1.428)
13  434.384 1.154   9.304   3   1   (8, 1.463)

我只有几分钟的时间，但这里有一个合适的代码的大纲，它假设你想同时将所有数据保存在内存中以进行一些跨行分析：

struct Data
{
    int a;
    float b, c, d;
    int e, f;
    std::vector<std::pair<int, float>> g;
};

int main()
{
    int line_num = 0;
    std::vector<Data> all_data;
    if (std::ifstream in(filename))
    {
        std::string line;
        while (getline(in, line))
        {
            ++line_num;
            std::istringstream iss(line);
            Data data;
            if (iss >> data.a >> data.b >> data.c >> data.d
                    >> data.e >> data.f)
            {
                int i; float f;
                while (iss >> i >> f)
                    data.g.push_back(std::make_pair(i, f));
                all_data.push_back(data);
            }
            else
                std::cerr << "unable to parse mandatory fields "
                    "from line #" << line_num << " '" << line
                    << "', ignoring and continuing...n"; 
        }
        ... use all_data for whatever analysis you want...
    }
    else
        std::cerr << "unable to open filen";
}

笔记

• 逐行读取，然后使用istringstream解析值
• 使用额外的循环来读取 - 行尾出现多对 int/float 值

您可以尝试使用 ifstream.getline（） 和 sscanf 的组合来处理该文件，它告诉它在字符串中找到了多少匹配项。

#include <iostream>
#include <fstream>
#include <cstdio>
int main(void)
{
    double a, b, c, d, e, f;
    int i, j, k, l, m, n;
    char buffer[160];
    std::ifstream file;
    file.open("data.txt");
    while (!file.eof()) {
        // check if this fails
        file.getline(buffer, 160);
        if (file.eof()) break;
        a = b = c = d = e = f = 0.0;
        i = j = k = l = m = n = 0;
        int res = sscanf(buffer,
                         "%d %lf %lf %lf %d %d %d %lf %d %lf %d %lf",
                         &i, &a, &b, &c, &j, &k, &l, &d, &m, &e, &n, &f);
        std::cout << "Got " << res << " fields" << std::endl;
    }
}`