How Does C Handle Static Initialization Order Fiasco in a Scenario with Circular Dependencies?

The Perplexity of Static Initialization Order Fiasco

In the realm of C , the "static initialization order fiasco" (SIOF) can introduce intricate complexities into code comprehension. The following code example illustrates this phenomenon:

// file1.cpp
extern int y;
int x = y + 1;

// file2.cpp
extern int x;
int y = x + 1;

Query:

Does this code snippet exhibit the following characteristics?

1. During compilation of file1.cpp, y is left uninitialized and no storage is allocated for it.
2. In file1.cpp, storage is allocated for x, but it is not initialized.
3. During compilation of file2.cpp, storage is allocated for y but without initialization.
4. If file2.o is initialized before file1.o during linking, what happens to x? Does it receive a default value of 0 or remain uninitialized?

Response:

The C standard (3.6.2 "Initialization of non-local objects") provides insight into the initialization steps:

1. Step 1: x and y are initialized to zero before any other initialization occurs.
2. Step 2: The standard does not specify whether x or y receives dynamic initialization first. However, the other variable will receive a value of 1 due to the zero initialization.
3. Step 3: Dynamic initialization occurs for the remaining variable, resulting in a value of 2.

Therefore, the answer to query 4 is that x receives a default value of 0 during initialization.

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