Containers (Modern C++)

By default, use vector as the default sequential container in C++. This is the equivalent of List<T> in other languages.

vector<string> v;
v.push_back( "Geddy Lee" );

Use map (not unordered_map) as the default associative container. Use set, multimap, multiset for degenerate & multi cases.

map<string, string> phone_book;
// ...
phone_book["Alex Lifeson"] = "+1 (416) 555-1212";

When performance optimization is needed, consider using:

1. the array type when embedding is important - for example, as a class member.

2. unordered associative containers (unordered_map, et al.): Lower per-element overhead (major) and constant-time lookup (potentially major, sometimes minor). Harder to use correctly and efficiently, because of inconveniences and sharp edges.

3. sorted vector. (See: Algorithms.)

Don’t use C arrays. (For older APIs, use f( vec.data(), vec.size() ); .)

For another article about containers, see STL Containers.

Container Sizes

The following tables show the container sizes, in bytes, for x86 and x64 platforms. (For these purposes, 32-bit ARM is equivalent to x86.) These tables cover release mode, because debug mode contains checking machinery that consumes space and time. The separate columns are for Visual C++ 2008 SP1, where _SECURE_SCL defaulted to 1, and for Visual C++ 2008 SP1 with _SECURE_SCL manually set to 0 for maximum speed. Visual C++ in Visual Studio 2010, Visual C++ in Visual Studio 2012, and Visual C++ in Visual Studio 2013 default _SECURE_SCL to 0 (now known as _ITERATOR_DEBUG_LEVEL).

x86 Container Sizes (Bytes)	VC9 SP1	VC9 SP1 SCL=0	VC10	VC11
vector<int>	24	16	16	12
array<int, 5>	20	20	20	20
deque<int>	32	32	24	20
forward_list<int>	N/A	N/A	8	4
list<int>	28	12	12	8
priority_queue<int>	28	20	20	16
queue<int>	32	32	24	20
stack<int>	32	32	24	20
pair<int, int>	8	8	8	8
tuple<int, int, int>	16	16	16	12
map<int, int>	32	12	16	8
multimap<int, int>	32	12	16	8
set<int>	32	12	16	8
multiset<int>	32	12	16	8
hash_map<int, int>	72	44	44	32
hash_multimap<int, int>	72	44	44	32
hash_set<int>	72	44	44	32
hash_multiset<int>	72	44	44	32
unordered_map<int, int>	72	44	44	32
unordered_multimap<int, int>	72	44	44	32
unordered_set<int>	72	44	44	32
unordered_multiset<int>	72	44	44	32
string	28	28	28	24
wstring	28	28	28	24

x64 Container Sizes (Bytes)	VC9 SP1	VC9 SP1 SCL=0	VC10	VC11
vector<int>	48	32	32	24
array<int, 5>	20	20	20	20
deque<int>	64	64	48	40
forward_list<int>	N/A	N/A	16	8
list<int>	56	24	24	16
priority_queue<int>	56	40	40	32
queue<int>	64	64	48	40
stack<int>	64	64	48	40
pair<int, int>	8	8	8	8
tuple<int, int, int>	16	16	16	12
map<int, int>	64	24	32	16
multimap<int, int>	64	24	32	16
set<int>	64	24	32	16
multiset<int>	64	24	32	16
hash_map<int, int>	144	88	88	64
hash_multimap<int, int>	144	88	88	64
hash_set<int>	144	88	88	64
hash_multiset<int>	144	88	88	64
unordered_map<int, int>	144	88	88	64
unordered_multimap<int, int>	144	88	88	64
unordered_set<int>	144	88	88	64
unordered_multiset<int>	144	88	88	64
string	40	40	40	32
wstring	40	40	40	32

See Also

Other Resources

Welcome Back to C++ (Modern C++)

C++ Language Reference

C++ Standard Library Reference