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Returns a reference to the mapped value of the element identified with key k.
If k does not match the key of any element in the container, the function throws an out_of_range exception.
If the map object is const-qualified, the function returns a reference to const mapped_type. Otherwise, it returns a reference to mapped_type.
Member type mapped_type is the type to the mapped values in the container (see map member types). In map this is an alias of its second template parameter (T).
Possible output:
The mapped value that is accessed may be modified by the caller. Concurrently accessing or modifying other elements is safe.
It throws out_of_range if k is not the key of an element in the map.
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
map
- map::~map
- map::map
member functions
-
map::atC++11
- map::begin
-
map::cbeginC++11
-
map::cendC++11
- map::clear
- map::count
-
map::crbeginC++11
-
map::crendC++11
-
map::emplaceC++11
-
map::emplace_hintC++11
- map::empty
- map::end
- map::equal_range
- map::erase
- map::find
- map::get_allocator
- map::insert
- map::key_comp
- map::lower_bound
- map::max_size
- map::operator[]
- map::operator=
- map::rbegin
- map::rend
- map::size
- map::swap
- map::upper_bound
- map::value_comp
-
non-member overloads
public member function
<map>
std::map::at
mapped_type& at (const key_type& k);const mapped_type& at (const key_type& k) const;
Access element
If k does not match the key of any element in the container, the function throws an out_of_range exception.
Parameters
- k
- Key value of the element whose mapped value is accessed.
Member type key_type is the type of the keys for the elements in the container, defined in map as an alias of its first template parameter (Key).
Return value
A reference to the mapped value of the element with a key value equivalent to k.If the map object is const-qualified, the function returns a reference to const mapped_type. Otherwise, it returns a reference to mapped_type.
Member type mapped_type is the type to the mapped values in the container (see map member types). In map this is an alias of its second template parameter (T).
Example
|
|
Possible output:
alpha: 10 beta: 20 gamma: 30 |
Complexity
Logarithmic in size.Iterator validity
No changes.Data races
The container is accessed (neither the const nor the non-const versions modify the container).The mapped value that is accessed may be modified by the caller. Concurrently accessing or modifying other elements is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.It throws out_of_range if k is not the key of an element in the map.
See also
- map::operator[]
- Access element (public member function)
- map::find
- Get iterator to element (public member function)
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Spotted an error? contact us