This class template implements a value‐semantic container type holding an ordered sequence of key‐value pairs having unique keys that provide a mapping from keys (of the template parameter type, KEY) to their associated values (of another template parameter type, VALUE).

Synopsis

Declared in <bslstl_map.h>

template<
    class KEY,
    class VALUE,
    class COMPARATOR = std::less<KEY>,
    class ALLOCATOR = allocator<pair<KEY const, VALUE>>>
class map;

Description

This class: * supports a complete set of value‐semantic operations

  • except for BDEX serialization * is exception‐neutral * is alias‐safe * is const thread‐safe For terminology see {`bsldoc_glossary`}.

Types

Name

Description

value_compare

This nested class defines a mechanism for comparing two objects of value_type by adapting an object of (template parameter) type COMPARATOR, which compares two objects of (template parameter) type KEY . Note that this class exactly matches its definition in the C++11 standard [map.overview]; otherwise, we would have implemented it as a separate component‐local class.

Type Aliases

Name

Description

allocator_type

Alias for the allocator type ALLOCATOR.

const_iterator

Constant bidirectional iterator over map elements.

const_pointer

Alias for the const pointer type supplied by the allocator traits.

const_reference

Alias for a constant reference to a map element.

const_reverse_iterator

Reverse iterator type for traversing the map in reverse order.

difference_type

Signed integer type measuring iterator distance.

iterator

Bidirectional iterator over map elements.

key_compare

Alias for the key‐comparison functor type COMPARATOR.

key_type

Alias for the key type KEY.

mapped_type

Alias for the mapped value type VALUE.

pointer

Alias for the pointer type supplied by the allocator traits.

reference

Alias for a modifiable reference to a map element.

reverse_iterator

Reverse iterator over map elements.

size_type

Alias for the size type supplied by the allocator traits.

value_type

Alias for the map element type pair<const KEY, VALUE>.

Member Functions

Name

Description

map [constructor]

Constructors

~map [destructor]

Destroy this object.

operator=

Assignment operators

at

at overloads

begin

begin overloads

cbegin

Return an iterator providing non‐modifiable access to the first value_type object in the ordered sequence of value_type objects maintained by this map, or the cend iterator if this map is empty.

cend

Return an iterator providing non‐modifiable access to the past‐the‐end element in the ordered sequence of value_type objects maintained by this map.

clear

Remove all entries from this map. Note that the map is empty after this call, but allocated memory may be retained for future use.

contains

Return true if this map contains an element whose key is equivalent to the specified key.

count

count overloads

crbegin

Return a reverse iterator providing non‐modifiable access to the last value_type object in the ordered sequence of value_type objects maintained by this map, or crend if this map is empty.

crend

Return a reverse iterator providing non‐modifiable access to the prior‐to‐the‐beginning element in the ordered sequence of value_type objects maintained by this map.

emplace

Insert into this map a newly‐created value_type object, constructed by forwarding get_allocator() (if required) and the specified (variable number of) args to the corresponding constructor of value_type, if a key equivalent to such a value does not already exist in this map; otherwise, this method has no effect (other than possibly creating a temporary value_type object). Return a pair whose first member is an iterator referring to the (possibly newly created and inserted) object in this map whose key is equivalent to that of an object constructed from args, and whose second member is true if a new value was inserted, and false if an equivalent key was already present. This method requires that the (template parameter) types KEY and VALUE both be emplace‐constructible from args (see {Requirements on KEY and VALUE}).

emplace_hint

Insert into this map a newly‐created value_type object, constructed by forwarding get_allocator() (if required) and the specified (variable number of) args to the corresponding constructor of value_type (in amortized constant time if the specified hint is a valid immediate successor to the value_type object constructed from args), if a key equivalent to such a value does not already exist in this map; otherwise, this method has no effect (other than possibly creating a temporary value_type object). Return an iterator referring to the (possibly newly created and inserted) object in this map whose key is equivalent to that of an object constructed from args. If hint is not a valid immediate successor to the value_type object implied by args, this operation has O[log(N)] complexity where N is the size of this map. This method requires that the (template parameter) types KEY and VALUE both be emplace‐constructible from args (see {Requirements on KEY and VALUE}). The behavior is undefined unless hint is an iterator in the range [begin() .. end()] (both endpoints included).

empty

Return true if this map contains no elements, and false otherwise.

end

end overloads

equal_range

equal_range overloads

erase

erase overloads

find

find overloads

get_allocator

Return (a copy of) the allocator used for memory allocation by this map.

insert

insert overloads

insert_or_assign

insert_or_assign overloads

insert_range

Insert into this map the value of each value_type object in the specified range if the key equivalent of that object is not already contained in this map. The (template parameter) type RANGE must meet the requirements the C++20 standard [ranges]providing access to values of a type convertible to value_type, and value_type must be emplace‐constructible from *i into this map, where i is a dereferenceable iterator obtained from range (see {Requirements on KEY and VALUE}). The behavior is undefined if range overlaps this map.

key_comp

Return the key‐comparison functor (or function pointer) used by this map; if a comparator was supplied at construction, return its value; otherwise, return a default constructed key_compare object. Note that this comparator compares objects of type KEY, which is the key part of the value_type objects contained in this map.

lower_bound

lower_bound overloads

max_size

Return a theoretical upper bound on the largest number of elements that this map could possibly hold. Note that there is no guarantee that the map can successfully grow to the returned size, or even close to that size without running out of resources.

operator[]

Subscript operators

rbegin

rbegin overloads

rend

rend overloads

size

Return the number of elements in this map.

swap

Exchange the value and comparator of this object with those of the specified other object; also exchange the allocator of this object with that of other if the (template parameter) type ALLOCATOR has the propagate_on_container_swap trait, and do not modify either allocator otherwise. This method provides the no‐throw exception‐safety guarantee if and only if the (template parameter) type COMPARATOR provides a no‐throw swap operation, and provides the basic exception‐safety guarantee otherwise; if an exception is thrown, both objects are left in valid but unspecified states. This operation has O[1] complexity if either this object was created with the same allocator as other or ALLOCATOR has the propagate_on_container_swap trait; otherwise, it has O[n + m] complexity, where n and m are the number of elements in this object and other, respectively. Note that this method's support for swapping objects created with different allocators when ALLOCATOR does not have the propagate_on_container_swap trait is a departure from the C++ Standard.

try_emplace

try_emplace overloads

upper_bound

upper_bound overloads

value_comp

Return a functor for comparing two value_type objects by comparing their respective keys using key_comp(). Note that this comparator compares objects of type value_type (i.e., bsl::pair<const KEY, VALUE>).

Specializations

Name

Description

map<TimeInterval, Node*>

This class template implements a value‐semantic container type holding an ordered sequence of key‐value pairs having unique keys that provide a mapping from keys (of the template parameter type, KEY) to their associated values (of another template parameter type, VALUE).

map<int, pair<shared_ptr<Statistics>, shared_ptr<Collector<OsLinux>>>>

This class template implements a value‐semantic container type holding an ordered sequence of key‐value pairs having unique keys that provide a mapping from keys (of the template parameter type, KEY) to their associated values (of another template parameter type, VALUE).

Deduction Guides

Name

Description

map<KEY, VALUE>

Deduce the template parameters KEY and VALUE from the value_type of the initializer_list supplied to the constructor of map. This deduction guide does not participate unless the supplied allocator is convertible to bsl::allocator<bsl::pair<const KEY, VALUE>>.

map<KEY, VALUE>

Deduce the template parameters KEY and VALUE from the value_type of the iterators supplied to the constructor of map. This deduction guide does not participate unless the supplied allocator is convertible to bsl::allocator<bsl::pair<const KEY, VALUE>>.

map<KEY, VALUE, COMPARATOR>

Deduce the template parameters KEY and VALUE from the value_type of the initializer_list supplied to the constructor of map. Deduce the template parameter COMPARATOR from the other parameters passed to the constructor. This deduction guide does not participate unless the supplied allocator is convertible to bsl::allocator<bsl::pair<const KEY, VALUE>>.

map<KEY, VALUE, COMPARATOR>

Deduce the template parameters KEY and VALUE from the value_type of the iterators supplied to the constructor of map. Deduce the template parameter COMPARATOR from the other parameter passed to the constructor. This deduction guide does not participate unless the supplied allocator is convertible to bsl::allocator<bsl::pair<const KEY, VALUE>>.

map<KEY, VALUE, COMPARATOR, ALLOCATOR>

Deduce the template parameters KEY and VALUE from the value_type of the initializer_list supplied to the constructor of map. Deduce the template parameters COMPARATOR and ALLOCATOR from the other parameters passed to the constructor. This deduction guide does not participate unless the supplied allocator meets the requirements of a standard allocator.

map<KEY, VALUE, COMPARATOR, ALLOCATOR>

Deduce the template parameters KEY and VALUE from the value_type of the iterators supplied to the constructor of map. Deduce the template parameters COMPARATOR and ALLOCATOR from the other parameters passed to the constructor. This deduction guide does not participate unless the supplied allocator meets the requirements of a standard allocator.

map<KEY, VALUE, std::less<KEY>, ALLOCATOR>

Deduce the template parameters KEY and VALUE from the value_type of the initializer_list supplied to the constructor of map. Deduce the template parameter ALLOCATOR from the other parameter passed to the constructor. This deduction guide does not participate unless the supplied allocator meets the requirements of a standard allocator.

map<KEY, VALUE, std::less<KEY>, ALLOCATOR>

Deduce the template parameters KEY and VALUE from the value_type of the iterators supplied to the constructor of map. This deduction guide does not participate unless the supplied allocator meets the requirements of a standard allocator.

Non-Member Functions

Name

Description

erase_if

Erase all the elements in the specified map m that satisfy the specified predicate predicate. Return the number of elements erased.

operator<=>

Perform a lexicographic three‐way comparison of the specified lhs and the specified rhs maps by using the comparison operators of bsl::pair<const KEY, VALUE> on each element; return the result of that comparison.

operator==

Return true if the specified lhs and rhs objects have the same value, and false otherwise. Two map objects lhs and rhs have the same value if they have the same number of key‐value pairs, and each element in the ordered sequence of key‐value pairs of lhs has the same value as the corresponding element in the ordered sequence of key‐value pairs of rhs. This method requires that the (template parameter) types KEY and VALUE both be equality‐comparable (see {Requirements on KEY and VALUE}).

swap

Exchange the value and comparator of the specified a object with those of the specified b object; also exchange the allocator of a with that of b if the (template parameter) type ALLOCATOR has the propagate_on_container_swap trait, and do not modify either allocator otherwise. This function provides the no‐throw exception‐safety guarantee if and only if the (template parameter) type COMPARATOR provides a no‐throw swap operation, and provides the basic exception‐safety guarantee otherwise; if an exception is thrown, both objects are left in valid but unspecified states. This operation has O[1] complexity if either a was created with the same allocator as b or ALLOCATOR has the propagate_on_container_swap trait; otherwise, it has O[n + m] complexity, where n and m are the number of elements in a and b, respectively. Note that this function's support for swapping objects created with different allocators when ALLOCATOR does not have the propagate_on_container_swap trait is a departure from the C++ Standard.

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