Why doUninitialized Local Variables in C Produce Undefined Behavior?

What is the Fate of Uninitialized Variables?

Consider the following code:

int main()
{
    int a;
    cout << a;
    return 0;
}

You might expect this code to output a garbage value, but instead, it outputs zero. This is because, while uninitialized local variables in C are technically indeterminate, their actual behavior becomes undefined if the value is used before being initialized.

However, global, thread-local, and static variables are all initialized to zero by default. Therefore, only local variables can introduce this undefined behavior.

To avoid potential issues, it is generally recommended to explicitly initialize all variables, especially global ones. However, there are rare exceptions where initializing global variables based on runtime values may be necessary, such as in embedded systems.

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