Are C# Local Variables Truly Uninitialized Before Explicit Assignment?

Are C# variables really uninitialized?

The C# specification stipulates that variables must be explicitly initialized before use. However, a common assumption is that runtime constraints prevent "unassigned" values ​​from existing. Specifically, reference types are considered to default to null rather than retaining residual values ​​from previous calls.

Truth: Qualified "is"

While some variables, such as array elements and fields, are automatically assigned default values, the situation is different for local variables. The compiler requires that local variables be "explicitly assigned" before they can be used. Although it's not explicitly stated in the question, the implication is whether these local variables are initially assigned in the same way as non-local variables.

The answer is yes. While the runtime technically allows local variables to be left in an uninitialized state, in practice this never happens. To ensure a predictable and reliable environment, local variables are aggressively zeroed.

Influence

Although the runtime prevents observation of uninitialized local variables, the prohibition against using unassigned local variables still exists. This is not to prevent exposure of uninitialized values, but to prevent errors that may arise from using them. By forcing explicit assignment, the compiler effectively eliminates the possibility of such errors.

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