How are Static and Global Variables Initialized in C and C ?

Initialization of Static and Global Variables in C and C

In C and C , static and global variables are crucial components of the initialization process prior to the main function. Understanding their behavior is essential for proper program execution.

Phase of Initialization

In C , static and global objects, defined at namespace scope, undergo three initialization phases:

• Zero initialization: All variables are initialized to zero.
• Static initialization: Variables with static initialization (typically using a constant value) are initialized.
• Dynamic initialization: Variables requiring code execution for initialization are handled.

Memory Allocation and Storage

During compilation, the compiler allocates space for static initialization variables in the .data segment of the executable. This segment is loaded into memory at program startup, enabling static initialization values like 5 and 4 to be readily available.

Zero Initialization

Variables without explicit initialization in C (e.g., global_int2, static_int2) are initialized to zero during zero initialization, which occurs before static initialization.

Execution of Initialization

For variables like global_int1 that have an explicit initializer (in this case, 5), the compiler stores the value in the .data segment to be assigned during initialization. Additionally, variables requiring code execution for initialization (dynamic initialization) are handled after static initialization.

Modern Implementations

While the concept of segments is still applicable, modern operating systems and compilers manage memory using more sophisticated techniques. Nonetheless, the principles outlined above remain valid in general.

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