How Does `array[100] = {0}` Initialize Arrays in C and C ?

Diving into Array Initialization: How does array[100] = {0} work its Wonders?

In the realm of programming, arrays play a vital role in organizing data. One intriguing aspect of arrays is the ability to assign a uniform value to all their elements using the notation array[size] = {value}. To unravel the mystery behind this seemingly effortless initialization, let us delve into the world of compilers.

Behind the Scenes: Compiler's Magic

When a compiler encounters an array declaration like char array[100] = {0}, it doesn't perform any sorcery to fill the array with zeros. Instead, it relies on well-defined rules outlined in programming language specifications.

In C, as stated in section 6.7.8.21 of its specification, any uninitialized elements in the array are automatically initialized to zero for arithmetic types. Additionally, pointers are set to NULL. This process is recursively applied to any nested arrays or structures within the main array.

In C , the behavior is slightly different. Section 8.5.1.7 of the C specification explains that the compiler performs aggregate-initialization on any uninitialized elements. Aggregate-initialization essentially means assigning the default values for the specific data type to those elements.

An Empty Embrace: Alternative Initialization Syntax

In C , there exists an alternative way to initialize arrays using an empty initializer list, denoted by array[size] = {}. When this is used, the compiler takes charge and aggregate-initializes all elements of the array.

Witnessing the Code Transformation

For those curious about the actual code generated by the compiler for such initializations, you can refer to a question on Stack Exchange titled "Strange assembly from array 0-initialization."

In summary, the compiler's ability to initialize arrays consistently stems from well-defined rules in programming language specifications. It achieves this without any mysterious tricks, ensuring reliable and predictable behavior for developers working with arrays.

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