c++ - 使用 boost program_options 处理帮助消息，删除默认值或重新格式化帮助消息

Question

我正在写一个涉及boost::program_options的C++程序，在这里我遇到了一些问题。这里给出了我的一些代码。

int main(int argc, char* argv[]) {
    options_description desc("useage: filterfq", options_description::m_default_line_length * 2, options_description::m_default_line_length);

    options_description generic("Gerneric options", options_description::m_default_line_length * 2, options_description::m_default_line_length);
    generic.add_options()
        ("help,h", "produce help message")
    ;

    options_description param("Parameters", options_description::m_default_line_length * 2, options_description::m_default_line_length);
    param.add_options()
        ("checkQualitySystem,c", bool_switch(), "only check quality system of the fastq file")
        ("baseNrate,N", value<float>() -> default_value(0.05), "maximum rate of \'N\' base allowed along a read")
        ("averageQuality,Q", value<float>() -> default_value(0), "minimum average quality allowed along a read")
        ("perBaseQuality,q", value<int>() -> default_value(5), "minimum quality per base allowed along a read")
        ("lowQualityRate,r", value<float>() -> default_value(0.5), "maximum low quality rate along a read")
        ("rawQualitySystem,s", value<int>(), "specify quality system of raw fastq\n0: Sanger\n1: Solexa\n2: Illumina 1.3+\n3: Illumina 1.5+\n4: Illumina 1.8+")
        ("preferSpecifiedRawQualitySystem,p", bool_switch(), "indicate that user prefers the given quality system to process")
    ;

    options_description input("Input", options_description::m_default_line_length * 2, options_description::m_default_line_length);
    input.add_options()
        ("rawFastq,f", value< vector<path> >() -> required() -> multitoken(), "raw fastq file(s) that need cleaned, required")
    ;

    options_description output("Output", options_description::m_default_line_length * 2, options_description::m_default_line_length);
    output.add_options()
        ("cleanQualitySystem,S", value<int>() -> default_value(4), "specify quality system of cleaned fastq, the same as rawQualitySystem")
        ("outDir,O", value<path>() -> default_value(current_path()), "specify output directory, not used if cleanFastq is specified")
        ("outBasename,o", value<string>(), "specify the basename for output file(s), required if outDir is specified")
        ("cleanFastq,F", value< vector<path> >() -> multitoken(), "cleaned fastq file name(s), not used if outDir or outBasename is specified")
        ("droppedFastq,D", value< vector<path> >() -> multitoken(), "fastq file(s) containing reads that are filtered out")
    ;

    desc.add(generic).add(param).add(input).add(output);

    variables_map vm;
    store(command_line_parser(argc, argv).options(desc).run(), vm);
    if (vm.count("help")) {
        cout << desc << "\n";
        return 0;
    }
    ...
}

这里没有给出#include using 命名空间部分。当我键入命令以查看帮助消息时，它向我显示了以下内容

useage: filterfq:

Gerneric options:
  -h [ --help ]         produce help message

Parameters:
  -c [ --checkQualitySystem ]               only check quality system of the fastq file
  -N [ --baseNrate ] arg (=0.0500000007)    maximum rate of 'N' base allowed along a read
  -Q [ --averageQuality ] arg (=0)          minimum average quality allowed along a read
  -q [ --perBaseQuality ] arg (=5)          minimum quality per base allowed along a read
  -r [ --lowQualityRate ] arg (=0.5)        maximum low quality rate along a read
  -s [ --rawQualitySystem ] arg             specify quality system of raw fastq
                                            0: Sanger
                                            1: Solexa
                                            2: Illumina 1.3+
                                            3: Illumina 1.5+
                                            4: Illumina 1.8+
  -p [ --preferSpecifiedRawQualitySystem ]  indicate that user prefers the given quality system to process

Input:
  -f [ --rawFastq ] arg raw fastq file(s) that need cleaned, required

Output:
  -S [ --cleanQualitySystem ] arg (=4)             specify quality system of cleaned fastq, the same as rawQualitySystem
  -O [ --outDir ] arg (="/home/tanbowen/filterfq") specify output directory, not used if cleanFastq is specified
  -o [ --outBasename ] arg                         specify the basename for output file(s), required if outDir is specified
  -F [ --cleanFastq ] arg                          cleaned fastq file name(s), not used if outDir or outBasename is specified
  -D [ --droppedFastq ] arg                        fastq file(s) containing reads that are filtered out

帮助信息看起来有点难看，尤其是“0.0500000007”，我想改进一下。但是我在谷歌上搜索了很长时间，我找不到解决方案。所以我在这里请求帮助解决以下问题:

1. 有什么方法可以重新格式化帮助信息吗？
2. 如果 1 不可能，如何去掉“arg”部分和默认值？
3. 有什么方法可以对齐右侧的描述吗？

一个额外的问题:我怎样才能阻止下面的命令被执行

filter -f <some file> -f <some file>

即，不允许多次指定相同的选项？

非常感谢!!

Answer 1

1. 是的，见下文(展示了收集和显示格式化选项的一般形式)

2. 查看options_description 的构造函数。它允许您指定列宽。

这是自定义选项值的(真实)示例。在我的例子中，我想收集一个以字节为单位的缓冲区大小，但也希望能够解析 4K 或 1M 之类的东西。

struct bytesize_option
{
    bytesize_option(std::size_t val = 0) : _size(val) {}

    std::size_t value() const { return _size; }
    void set(std::size_t val) { _size = val; }

private:
    std::size_t _size;
};

std::ostream& operator<<(std::ostream& os, bytesize_option const& hs);
std::istream& operator>>(std::istream& is, bytesize_option& hs);

namespace {
    static constexpr auto G = std::size_t(1024 * 1024 * 1024);
    static constexpr auto M = std::size_t(1024 * 1024);
    static constexpr auto K = std::size_t(1024);
}

std::ostream& operator<<(std::ostream& os, bytesize_option const& hs)
{
    auto v = hs.value();
    if (v % G == 0) { return os << (v / G) << 'G'; }
    if (v % M == 0) { return os << (v / M) << 'M'; }
    if (v % K == 0) { return os << (v / K) << 'K'; }
    return os << v;
}

std::istream& operator>>(std::istream& is, bytesize_option& hs)
{
    std::string s;
    is >> s;
    static const std::regex re(R"regex((\d+)([GMKgmk]){0,1})regex");
    std::smatch match;
    auto matched = std::regex_match(s, match, re);
    if(!matched) {
        throw po::validation_error(po::validation_error::invalid_option_value);
    }
    if (match[2].matched)
    {
        switch (match[2].str().at(0))
        {
            case 'G':
            case 'g':
                hs.set(std::stoul(match[1].str()) * G);
                break;
            case 'M':
            case 'm':
                hs.set(std::stoul(match[1].str()) * M);
                break;
            case 'K':
            case 'k':
                hs.set(std::stoul(match[1].str()) * K);
                break;
        }
    }
    else {
        hs.set(std::stoul(match[1].str()));
    }
    return is;
}

你会像这样使用它:

    return boost::shared_ptr<po::option_description> {
        new po::option_description("server.max-header-size,x",
                                   po::value(&_max_hdr_size)
                                   ->default_value(_max_hdr_size),
                                   "The maximum size (in bytes) of a HTTP header "
                                   "that the server will accept")
    };

在这种情况下，定义了 _max_hdr_size:

bytesize_option _max_hdr_size;