Checking if any particular element exists or not in the C ++ STL vector

Question

I wanted to check if an element exists in a specific vector location, say i, before accessing it like v [i]. Could you tell me how can I do this?

Thanks.

Answer 1

if (0 <= i  &&  i < v.size()) {
  // OK
  std::cout << v[i]; // Example
} else {
  // Wrong
}

Answer 2

An element is guaranteed to exist in every position i, where i >= 0and i < v.size(), since vectors are adjacent sequences of elements and “holes”, it is impossible.

Answer 3

v.size().

Answer 4

, , , , .

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Answer 5

I understand that you have std::vectorprealocated in a specific dimension, say n, and you want to find out if an element in index i( i < n) was initialized or just highlighted .

Like @Thomas Matthews, you can use a second data structure, a simple bool[n]one in which kyou store in the index trueif the element with the index kin yours vectorexists falseotherwise.

      0 1 2 3 4 5
v = [ *   *   * * ]

             0     1      2     3     4     5
exists = [ true, false, true, false, true, true ]