Consider the following
int x;This is default-initialization. This defines the variable with a garbage value (not zero). If we print its contents, it will be whatever value is sitting at that memory address. Who knows!
When you don’t initialize a variable, C++ populates it with whatever contents that memory address holds. These are called garbage values.
This form of initialization is inherited from C back when computers were slow and gas was 50 cents a gallon.
Don’t confuse this with value-initialization
This is different than int myArray[10] {}; This performs value-initialization. The 10 elements are initialized with zero.
No garbage values.
This works on other types:
int x {}; // Initializes to 0
std::string name; // name is "" (class types self-initialize)Undefined behaviour
Some compilers produce an error for uninitialized variables. For example in this program, GCC produces this warning → 8 | int x; // Allocation without initialization
#include <iostream>
int main() {
int x; // Defined only
// Let's read it
std::cout << "The value of x is: " << x << '\n';
}When I run it, I receive this random result
The value of x is: 32758
Ultimately…
Since we’re professionals, avoid undefined behaviour at all costs.
Always initialize your built-in types.