What Happens When You Define a Zero-Sized Array in C/C ?

Impact of Defining a 0-Size Array in C/C

When defining an array in C/C , the size of the array must be specified. Curiosity often arises about the behavior of defining an array with a size of zero, as is the case with int array[0].

In the provided code example, GCC does not raise any errors or warnings when compiling. This raises the question of whether zero-length arrays are optimized out during compilation.

According to the ISO 9899:2011 (C99) standard, an array cannot have a size of zero. The standard explicitly states that if the size of an array is a constant expression, it must have a value greater than zero. This rule applies to both plain arrays and variable length arrays (VLAs).

Despite the language standard, some compilers may allow the definition of zero-size arrays for legacy compatibility or specific purposes. However, it is not guaranteed that the behavior of zero-size arrays will be consistent across different compilers, and attempting to access a zero-size array is likely to result in undefined behavior.

As such, it is recommended to avoid defining zero-size arrays and to handle cases where the array size may be zero by other means, such as conditionally allocating memory.

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