Are thread_local Variables Implicitly Static in Block Scope?

Are Variables Declared with thread_local Automatically Static?

The following code segments appear identical at a glance:

<code class="cpp">void f() {
    thread_local vector<int> V;
    // ...
}

void f() {
    static thread_local vector<int> V;
    // ...
}</code>

However, the C Standard reveals a subtle difference. When defining a thread_local variable with block scope, the static storage class specifier is implied if not explicitly stated. This means that the first code segment is equivalent to the second.

Despite their similar definitions, static and thread_local variables differ significantly. Variables with static storage duration are associated with the entire program, while thread_local variables are associated with individual threads. Each thread has its own distinct object or reference associated with the thread_local variable.

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