← Patterns
Check existence of a key
123456789101112 | #include <map>
#include <string>
int main()
{
std::map<std::string, int> m = {{"a", 1}, {"b", 2}, {"c", 3}};
if (m.count("b"))
{
// We know "b" is in m
}
} |
This pattern is licensed under the CC0 Public Domain Dedication.
Requires
c++11
or newer.
Intent
Check if a particular key is in an associative container.
Description
On line 6, we create a std::map as an example
associative container and initialize it with key-value pairs.
On line 8, we count the number of occurrences of the key "b" in m
by using the member function count.
If "b" is in m, count will return 1; otherwise it will return
0.
Note: in C++14, an instance of the searched key will not be created if the container’s comparator is transparent and supports the appropriate comparison without conversions.
