Convert multi-line if statment to single line with map

Question

Note: c++98

I am a little new to C++ and I want to clean my code up. I have an if statment that checks the data type in an array, and if it matches then it is to execute the corresponding statement.

I want to convert this multi-line if statment to a single line that checks if any of these types exist in the map, and if they do execute it.

My code:

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
            }

and would like to convert it similar to something like:

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
}

Why do you want to use a `map`? You can use a `vector`: https://stackoverflow.com/q/571394/3684343 — mch, Jun 10 '20 at 08:32

score 1 · Accepted Answer · answered Jun 10 '20 at 13:43

I suppose the real challenge is to have a map<> that compares the keys case-insensitively.

You do that by using a comparison predicate:

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

You declare the map to use that predicate:

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

Some tests: 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";
    }
}

Prints

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

Flipping Key/Value

Dictionaries have a key field for lookup in all languages/libraries. So, to lookup in reverse you end up doing a linear search (just look at each element).

In Boost you can have your cake and eat it by defining a Multi Index Container.

Multi Index

This can facilitate lookup by multiple indices, including composite keys. (Search my answers for more real-life examples)

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";
        }
    }
}

Prints

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

Bimaps

Boost Bimap is a specialization of that for maps. It has fewer options, and notably adds operator[] style interface back.

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

Sadly the constructor doesn't support initializaer lists, but we can use the iterator interface, and then we use the right view of the bimap to do lookups by name:

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";
    }
}

Prints

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

darune · Answer 2 · 2020-06-10T09:09:14.443

I think you switched around the key and id in your example, judging by your description.

However, you can do what you want fairly easily by introducing a custom compare for the map. An easy way is to create a lambda function first:

auto compare = [](const std::string& a, const std::string& b) {return boost::iequals(a, b); };

std::map < std::string, int, decltype(compare)> mymap = { {"INT", 1},{"BIGINT", 2 }};//and so on

Then you can do:

if (mymap.count(sqlBufferTypes[i][j])) {//in c++20 can use "contains" instead of "count"
  //do stuff
}

If all you want do is check and dont need the ID later, then you should use a std::set instead of map.

c++98 NOTE

In c++98 you cannot use a lambda, however you can still make the compare predicate with a regular struct:

struct compare : public std::binary_function<string, string, bool>
{
    bool operator()(const string& a, const string& b) const
    {
        return boost::iequals(a,b);
    }
};

Convert multi-line if statment to single line with map

2 Answers2

Flipping Key/Value

Multi Index

Bimaps