CmdLineParser.cpp

#include <string>
#include <iostream>
#include <unordered_map>

class CmdLineParser {
public:
    CmdLineParser(int args, char** argv) {
        try {
            for(size_t i = 1; i < args; ++i) {
                enum class State {
                    kKEY, kVAL, kEQUAL, kOTHER
                };

                auto state = State::kOTHER;

                const char* line = argv[i];
                size_t curse = 0;
                size_t begin = 0;

                std::string k, v;

                bool shutdown = false;

                while(!shutdown) {
                    switch (state) {
                        case State::kKEY:
                            if (std::isalpha(line[curse]) || std::isdigit(line[curse])) {
                                ++curse;
                                continue;
                            }

                            switch (line[curse]) {
                                case '=':
                                    state = State::kEQUAL;
                                    k = std::string(line + begin, line + curse);
                                    while(!k.empty() and (k.back() == ' ' or k.back() == '\t'))
                                        k.pop_back();
                                    ++curse;
                                    begin = curse + 1;
                                    continue;
                                case ' ':
                                case '\t':
                                    ++curse;
                                    continue;
                            }

                            throw std::logic_error("CmdLineParser: Syntax error(syntax: .^*k{empty}^*={empty}^v.^*)");
                        case State::kEQUAL:
                            if (line[curse] > 32 and line[curse] <= 126) {
                                state = State::kVAL;
                                begin = curse;
                                continue;
                            }
                            ++curse;
                            break;
                        case State::kVAL:
                            if (line[curse] > 32 and line[curse] <= 126)
                                ++curse;
                            else {
                                v = std::string(line + begin, line + curse);
                                shutdown = true;
                            }
                            break;
                        case State::kOTHER:

                            if (std::isalpha(line[curse])) {
                                state = State::kKEY;
                                begin = curse;
                                continue;
                            }

                            // Default
                            ++curse;
                            break;
                    }
                }

                if (k.empty() or v.empty())
                    throw std::logic_error("CmdLineParser: Syntax error(syntax: .^*k{empty}^*={empty}^v.^*)");

                std::cout << "[CmdLineParser] Key: " << k << '=' << v << std::endl;

                m_kv[k] = v;
            }
        } catch (const std::logic_error& err) {
            std::cerr << err.what() << std::endl;
        }
    }

    std::string Get(const std::string& k) const {
        auto res = m_kv.find(k);
        return m_kv.cend() == res ? std::string{} : (res->second);
    }

    const std::unordered_map<std::string, std::string>& Get() {
        return m_kv;
    }
private:
    std::unordered_map<std::string, std::string> m_kv;
};

int main(int args, char** argv) {
    CmdLineParser parser(args, argv);
    for (auto&& p : parser.Get())
        std::cout << p.first << ' ' << p.second << std::endl;
    std::cout << parser.Get("hello");
}