C++ initialize map of pairs

Question

I want to statically initialize a map<string, pair<some_enum, string> >. Let's say a map from employee id to job title (enum) + name.

I would love for it to look like this:

map<string, pair<some_enum, string> > = {
  { "1234a", { BOSS, "Alice" }},
  { "5678b", { SLAVE, "Bob" }},
  { "1111b", { IT_GUY, "Cathy" }},
};

What is the best way to do this in C++?

The best way is how you have it. I also like how you have it sorted by job title. — chris, Aug 22 '14 at 18:07
[Works for me](http://ideone.com/Jzvi1f). What seem to be the problem? — Igor Tandetnik, Aug 22 '14 at 18:08
This should work if you use a compiler compatible with C++11 standard. — Sergey Kalinichenko, Aug 22 '14 at 18:10

cubuspl42 · Answer 1 · 2014-08-22T18:16:43.150

7

The best way in C++11:

std::map<string, pair<some_enum, std::string>> my_map = {
  { "1234a", { BOSS, "Alice" }},
  { "5678b", { SLAVE, "Bob" }},
  { "1111b", { IT_GUY, "Cathy" }},
};

It's that easy.

It's not possible at all in standard C++03 without using external libraries like boost.

edited Aug 22 '14 at 18:16

answered Aug 22 '14 at 18:11

cubuspl42

7,833
4
41
65

1

C++03 isn't *too* bad. Something like `boost::whatever_map_list_of("1234a", std::make_pair(BOSS, "Alice"))("5678b", …)` – chris Aug 22 '14 at 18:13
Hmm, I was thinking about standard C++. I'll let other talk about boost, because I don't have much experience with it. – cubuspl42 Aug 22 '14 at 18:15

cdhowie · Accepted Answer · 2014-08-22T18:21:08.397

7

In C++11, what you have works fine (assuming you add an identifier name to the variable declaration).

In versions prior, one approach would be to have a free function that builds the map:

typedef std::map<std::string, std::pair<some_enum, std::string> > map_type;

static map_type create_map()
{
    map_type map;

    map["1234a"] = std::make_pair(BOSS, "Alice");
    map["5678b"] = std::make_pair(SLAVE, "Bob");
    map["1111b"] = std::make_pair(IT_GUY, "Cathy");

    return map;
}

map_type foo = create_map();

Or you can make use of Boost.Assign:

std::map<std::string, std::pair<some_enum, std::string> > foo =
    boost::assign::map_list_of("1234a", std::make_pair(BOSS, "Alice"))
                              ("5678b", std::make_pair(SLAVE, "Bob"))
                              ("1111b", std::make_pair(IT_GUY, "Cathy"));

edited Aug 22 '14 at 18:21

answered Aug 22 '14 at 18:14

cdhowie

158,093
24
286
300

(missing brackets after make_pair) – Piotr Skotnicki Aug 22 '14 at 18:17
2

@PiotrS. They are not required; the compiler will infer the template type arguments. (That's the whole reason for `std::make_pair` -- if you were going to specify the template type arguments yourself you could just use the `std::pair` constructor directly.) – cdhowie Aug 22 '14 at 18:17
1

I meant () brackets, not <> – Piotr Skotnicki Aug 22 '14 at 18:20
@PiotrS. Ah, you meant parens. Good catch, I will fix that. – cdhowie Aug 22 '14 at 18:21
2

If there's one thing I've learned from SO, it's to never say brackets and expect people to know which kind you're talking about. – chris Aug 22 '14 at 18:22

C++ initialize map of pairs

2 Answers2