c++ - 使用 boost::spirit 在 C++ 中读取二维数组

Question

我想读取一个简单的 2D int 数组(空格分隔)为 here :

qi::phrase_parse(b, e, +qi::int_ % qi::eol, qi::space - qi::eol, vectors)

但是有两个区别:

1. 我想将它逐行放入一维 std::vector 中，不分开
2. 如果两行有不同数量的整数，这将被识别为解析错误。

是否可以将其作为一个类轮来执行，例如不写我自己的解析器？就像 the link mentioned above 中一样简单？

Answer 1

假设您指的是 Spirit 版本(“作为一个内衬”)，下面是一个添加了元素数量检查的改编版本。

如果您想要更多的控制权(并即时检查输入，而不是“事后诸葛亮”)，那么我建议您查看我写的另一个答案，其中显示了执行此操作的三种方法:

• Boost::Spirit::QI parser: index of parsed element

.

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/support_istream_iterator.hpp>
#include <boost/spirit/include/karma.hpp>

namespace spirit = boost::spirit;
namespace qi     = boost::spirit::qi;
namespace karma  = boost::spirit::karma;

int main()
{
    std::cin.unsetf(std::ios::skipws);
    spirit::istream_iterator b(std::cin), e;

    std::vector<std::vector<int> > vectors;

    if (qi::phrase_parse(b, e, +qi::int_ % qi::eol >> qi::eoi, qi::blank, vectors))
    {
        std::cerr << "Parse failed at '" << std::string(b,e) << "'\n";
        return 255;
    }

    // check all rows have equal amount of elements:
    const auto number_of_elements = vectors.front().size();
    for (auto& v : vectors)
        if (v.size() != number_of_elements)
            std::cerr << "Unexpected number of elements: " << v.size() << " (expected: " << number_of_elements << ")\n";

    // print the data for verification
    std::cout 
        << karma::format(karma::right_align(8)[karma::auto_] % ',' % '\n', vectors)
        << std::endl;

    return 0;
}

^{karma 位不是必需的(它们只是为了演示而输出整个内容)。}

更新

要构建更主动的错误检查，您可以:

int num_elements = 0;
bool ok = qi::phrase_parse(b, e, 
        (+qi::int_) [ phx::ref(num_elements) = phx::size(qi::_1) ]
     >> *(qi::eol >> qi::repeat(phx::ref(num_elements)) [ qi::int_ ])
     >> *qi::eol, 
     qi::blank, vectors);

它使用 qi::repeat 期望后续行中有 num_elements 个元素。您可以将其存储到一维数组中:

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/support_istream_iterator.hpp>
#include <boost/spirit/include/karma.hpp>

namespace qi     = boost::spirit::qi;
namespace phx    = boost::phoenix;
namespace karma  = boost::spirit::karma;

int main()
{
    std::cin.unsetf(std::ios::skipws);
    boost::spirit::istream_iterator b(std::cin), e;

    //std::vector<std::vector<int> > vectors;
    std::vector<int> vectors;

    int num_elements = 0;
    bool ok = qi::phrase_parse(b, e, 
            (+qi::int_) [ phx::ref(num_elements) = phx::size(qi::_1) ]
         >> *(qi::eol >> qi::repeat(phx::ref(num_elements)) [ qi::int_ ])
         >> *qi::eol, 
         qi::blank, vectors);

    std::cout << "Detected num_elements: " << num_elements << "\n";

    if (!ok)
    {
        std::cerr << "Parse failed at '" << std::string(b,e) << "'\n";
        return 255;
    }

    if (b!=e)
        std::cout << "Trailing unparsed: '" << std::string(b,e) << "'\n";

    // print the data for verification
    std::cout 
        << karma::format_delimited(karma::columns(num_elements)[+karma::int_], ' ', vectors)
        << std::endl;

    return 0;
}

^{请注意使用 karma::columns(num_elements) 将输出拆分为每行正确的列数。}