c++ - 使用 map 将多行 if 语句转换为单行

Question

注:c++98

我对 C++ 有点陌生，我想清理我的代码。我有一个 if 语句检查数组中的数据类型，如果匹配，则执行相应的语句。

我想将此多行 if 语句转换为单行，以检查 map 中是否存在任何这些类型，以及它们是否执行它。

我的代码:

if (boost::iequals(sqlBufferTypes[i][j], "INTEGER")                 ||
                boost::iequals(sqlBufferTypes[i][j], "INT")         ||
                boost::iequals(sqlBufferTypes[i][j], "BIGINT")      ||
                boost::iequals(sqlBufferTypes[i][j], "uint8_t")     ||
                boost::iequals(sqlBufferTypes[i][j], "uint16_t")    ||
                boost::iequals(sqlBufferTypes[i][j], "LONG"))
            {
                // do stuff
            }

并希望将其转换为类似于:

map<int, string> dataTypes;

dataTypes[1,"INT"];
dataTypes[2,"BIGINT"];
dataTypes[3,"uint8_t"];
dataTypes[4,"uint16_t"];
dataTypes[5,"LONG"];

if (boost::iequals(dataTypes.begin(), dataTypes.end())
{
    // do stuff
}

Answer 1

我想 真实 挑战是拥有一个map<>不区分大小写地比较键。

您可以通过使用比较谓词来做到这一点:

struct ci_less {
    bool operator()(std::string_view a, std::string_view b) const {
        return boost::lexicographical_compare(a, b, boost::is_iless{});
    }
};

您声明 map 以使用该谓词:

std::map<std::string, int, ci_less> const dataTypes {
    { "INT",      1 },
    { "BIGINT",   2 },
    { "uint8_t",  3 },
    { "uint16_t", 4 },
    { "LONG",     5 },
};

Note that it is now const, and I flipped the key/value pairs. See below

一些测试: Live On Coliru

// your sqlBufferTypes[i][j] e.g.:
for (std::string const key : { "uint32_t", "long", "lONg" }) {
    if (auto match = dataTypes.find(key); match != dataTypes.end()) {
        std::cout << std::quoted(key) << " maps to " << match->second;

        // more readable repeats lookup:
        std::cout << " or the same: " << dataTypes.at(key) << "\n"; // throws unless found
    } else {
        std::cout << std::quoted(key) << " not found\n";
    }
}

打印

"uint32_t" not found
"long" maps to 5 or the same: 5
"lONg" maps to 5 or the same: 5

翻转键/值

字典有一个用于在所有语言/库中查找的关键字段。因此，要反向查找，您最终会进行线性搜索(只需查看每个元素)。

在助推你 可以通过定义一个多索引容器来吃你的蛋糕。

多指标

这有助于通过多个索引(包括复合键)进行查找。 (搜索我的答案以获取更多真实示例)

Live On Coliru

#include <boost/algorithm/string.hpp> // for is_iless et al.
#include <string_view>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <iostream> // for std::cout
#include <iomanip> // for std::quoted
#include <boost/locale.hpp>

namespace bmi = boost::multi_index;

struct ci_less {
    bool operator()(std::string_view a, std::string_view b) const {
        return boost::lexicographical_compare(a, b, boost::is_iless{});
    }
};

struct DbType {
    std::string_view name;
    int type_id;

    friend std::ostream& operator<<(std::ostream& os, DbType const& t) {
        return os << "DbType{" << std::quoted(t.name) << ", " << t.type_id << "}";
    }
};

using Map = bmi::multi_index_container<
    DbType,
    bmi::indexed_by<
        bmi::ordered_unique<
            bmi::tag<struct by_id>,
            bmi::member<DbType, int, &DbType::type_id> >,
        bmi::ordered_unique<
            bmi::tag<struct by_name>,
            bmi::member<DbType, std::string_view, &DbType::name>, ci_less>
    >
>;

int main() {

    Map dataTypes {
        { "INT",      1 },
        { "BIGINT",   2 },
        { "uint8_t",  3 },
        { "uint16_t", 4 },
        { "LONG",     5 },
    };

    auto& idx = dataTypes.get<by_name>();

    // your sqlBufferTypes[i][j] e.g.:
    for (std::string_view const key : { "uint32_t", "long", "lONg" }) {
        if (auto match = idx.find(key); match != idx.end()) {
            std::cout << std::quoted(key) << " -> " << *match << std::endl;
        } else {
            std::cout << std::quoted(key) << " not found\n";
        }
    }
}

打印

"uint32_t" not found
"long" -> DbType{"LONG", 5}
"lONg" -> DbType{"LONG", 5}

双图

Boost Bimap 是 map 的专门化。它的选项更少，尤其是增加了 operator[]风格界面回来了。

using Map = boost::bimap<
    int,
    boost::bimaps::set_of<std::string_view, ci_less>>;

遗憾的是构造函数不支持初始化列表，但我们可以使用迭代器接口(interface)，然后我们使用 right按名称进行查找的 bimap View :

Live On Coliru

static const Map::relation s_mappings[] = {
    { 1, "INT" },
    { 2, "BIGINT" },
    { 3, "uint8_t" },
    { 4, "uint16_t" },
    { 5, "LONG" },
};

Map const dataTypes { std::begin(s_mappings), std::end(s_mappings) };

// your sqlBufferTypes[i][j] e.g.:
auto& vw = dataTypes.right;
for (std::string_view const key : { "uint32_t", "long", "lONg" }) {
    if (auto match = vw.find(key); match != vw.end()) {
        std::cout << std::quoted(key) << " -> " << match->second << "\n";
    } else {
        std::cout << std::quoted(key) << " not found\n";
    }
}

打印

"uint32_t" not found
"long" -> 5
"lONg" -> 5