Convert multi-line if statment to single line with map - c++

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
}

Answer 1

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

Answer 2

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);
}
};