I'm new in stl c++, someone can explain [](int x)?

Question

is_partitioned(vect.begin(), vect.end(), [](int x)
    { return x%2==0;})? cout << "Vector is partitioned": cout << "Vector is not partitioned";
    cout << e

ndl;

I'm unable to understand this code due to [](int x). please help

Answer 1

The [](int x) is actually just a part of the unnamed lambda function object:

// Return true if x is divisible by 2, false otherwise
[] (int x) { return x%2 == 0; } // lambda that acts as a predicate

• [] denotes a capture list

• (int x) is a parameter list

• {...} part is the body

Where the later two are just like in regular functions.

You supply this function (function object) as a predicate to the algorithm is_partitioned, so to have a custom predicate. Note, that the is_partitioned, in this case, has the following form:

is_partitioned(first, last, predicate); // Where the predicate is the lambda

For more information, refer to the documentation.