c++ - 防止循环内外的代码重复

Question

我在重写循环时遇到问题:

else if( "d" == option || "debug" == option )
{
    debug(debug::always) << "commandline::set_internal_option::setting debug options: "
                         << value << ".\n";
    string::size_type index = 0;
    do
    {
        const string::size_type previous_index = index+1;
        index=value.find( ',', index );
        const string item = value.substr(previous_index, index);
        debug::type item_enum;
        if( !map_value(lib::debug_map, item, item_enum) )
            throw lib::commandline_error( "Unknown debug type: " + item, argument_number );

        debug(debug::always) << "commandline::set_internal_option::enabling " << item
                             << " debug output.\n";
        debug(debug::always) << "\n-->s_level=" << debug::s_level << "\n";
        debug::s_level = static_cast<debug::type>(debug::s_level ^ item_enum);
        debug(debug::always) << "\n-->s_level=" << debug::s_level << "\n";
    } while( index != string::npos );
}

value 类似于 string("commandline,parser") 问题是在第一次运行时，我需要 substr(previous_index, index) ，但在每次后续迭代中，我都需要 substr(previous_index+1, index) 来跳过逗号。是否有一些我忽略的简单方法，或者我是否必须在初始迭代的循环外重复调用 find？

Answer 1

由于您的目标是防止代码重复:

std::vector<std::string> v;
boost::split(v, value, [](char c) { c == ','; });

如果你想创建自己的拆分函数，你可以这样做:

template<typename PredicateT>
std::vector<std::string> Split(const std::string & in, PredicateT p)
{
    std::vector<std::string> v;
    auto b = in.begin();
    auto e = b;
    do {
        e = std::find_if(b, in.end(), p);
        v.emplace_back(b,e);
        b = e + 1;        
    } while (e != in.end());

    return v;
}