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C++ Map Library - at() Function
Description
The C++ function std::map::at() returns a reference to the mapped value associated with key k.
Declaration
Following is the declaration for std::map::at() function form std::map header.
C++11
mapped_type& at (const key_type& k); const mapped_type& at (const key_type& k) const;
Parameters
k − Key value whose mapped value is accessed.
Return value
If object is constant qualified then method returns constant reference to mapped value otherwise returns non-constant reference.
Exceptions
If key is not present then method returns out_of_range exception.
Time complexity
Logarithmic i.e. log(n).
Example
The following example shows the usage of std::map::at() function.
#include <iostream> #include <map> using namespace std; int main(void) { /* Initializer_list constructor */ map<char, int> m = { {'a', 1}, {'b', 2}, {'c', 3}, {'d', 4}, {'e', 5}, }; cout << "Value of key m['a'] = " << m.at('a') << endl; try { m.at('z'); } catch(const out_of_range &e) { cerr << "Exception at " << e.what() << endl; } return 0; }
Let us compile and run the above program, this will produce the following result −
Value of key m['a'] = 1 Exception at map::at
map.htm
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