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C++ Map Library - operator[] Function
Description
The C++ function std::map::operator[] if key k matches an element in the container, then method returns a reference to the element.
Declaration
Following is the declaration for std::map::operator[] function form std::map header.
C++98
mapped_type& operator[] (const key_type& k);
C++11
mapped_type& operator[] (const key_type& k);
Parameters
k − Key of the element whose mapped value is accessed.
Return value
Returns a reference to the element associated with key k.
Exceptions
This member doesn't throw exception.
Time complexity
Logarithmic i.e. O(lon n)
Example
The following example shows the usage of std::map::operator[] 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 << "Map contains following elements" << endl; cout << "m['a'] = " << m['a'] << endl; cout << "m['b'] = " << m['b'] << endl; cout << "m['c'] = " << m['c'] << endl; cout << "m['d'] = " << m['d'] << endl; cout << "m['e'] = " << m['e'] << endl; return 0; }
Let us compile and run the above program, this will produce the following result −
Map contains following elements m['a'] = 1 m['b'] = 2 m['c'] = 3 m['d'] = 4 m['e'] = 5
map.htm
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