Variable initialization in C++

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It will be automatically initialized if

  • it’s a class/struct instance in which the default constructor initializes all primitive types; like MyClass instance;
  • you use array initializer syntax, e.g. int a[10] = {} (all zeroed) or int a[10] = {1,2}; (all zeroed except the first two items: a[0] == 1 and a[1] == 2)
  • same applies to non-aggregate classes/structs, e.g. MyClass instance = {}; (more information on this can be found here)
  • it’s a global/extern variable
  • the variable is defined static (no matter if inside a function or in global/namespace scope) – thanks Jerry

Never trust on a variable of a plain type (int, long, …) being automatically initialized! It might happen in languages like C#, but not in C & C++.

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