Can GCC Declare Array Sizes with Non-Constant Variables?

Declaring Array Size with Non-Constant Variable: A GCC Extension

Despite the general understanding that array size declarations in C require constant integer values, it has been observed that certain code, such as:

<code class="cpp">int ArraySize = 5;
int MyArray[ArraySize];</code>

compiles successfully in some environments. This exception arises from a GCC extension.

As per the C guidelines, the array bound should be a constant expression. The explanation from The C Programming Language by Bjarne Stroustrup also reinforces this notion. However, GCC allows the use of non-constant variables for array size declarations as an extension to the standard.

For those prioritizing portability, it is recommended to use the '-pedantic' option to receive a warning for such extensions. Alternatively, '-std=c 98' can be employed to treat it as an error and ensure adherence to the standard.

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