What are Variable-Length Arrays (VLAs) in C and C , and why are they disallowed in global scope?

Variable-Length Arrays (VLA) in C and C

Variable-length arrays (VLAs) are arrays whose size is not known at compile time but can be determined at runtime. This allows programmers to create arrays with sizes that are based on user input or dynamic conditions.

In C99 and later, VLAs can be declared in local scopes, but they cannot be declared in global scopes. This is because global variables must have a fixed size known at compile time.

In your example, the VLA array is declared in the local scope of the main function. Since the size of the array is not known at compile time, it is determined at runtime based on the value of the size variable.

However, the global variable global_array cannot be declared as a VLA because its size is not determined at compile time. The const modifier does not create a compile-time value in C99, but it does in C . Therefore, in C99, global_array is treated as a VLA, while in C , it is not.

VLAs are not allowed in global scope because it is difficult to manage their memory and ensure that the allocated memory is released properly. Additionally, if a VLA is passed to a function, the function must know the size of the array. This can be problematic if the function is used in multiple projects with different array sizes.

In conclusion, your reasoning about VLAs in C and C is correct. The behavior you described is accurate, and VLAs are not allowed in global scope to ensure memory management and proper code functionality.

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