ISO C90 forbids variable length array
c, variable-length-array
Solution
`const`-qualifying a variable doesn't make it a compile-time constant (see C99 6.6 §6 for the defintion of an integer constant expression), and before the introduction of variable-length arrays with C99, array sizes needed to be compile-time constants.
It's rather obvious that `const`-qualify a variable doesn't make it a compile-time constant, in particular in case of function parameters which won't be initialized until the function is called.
I see the following solutions to your problem:
- compile your code as C99 via `-std=c99` or `-std=gnu99`
- allocate your buffer via `malloc()`
- use `alloca()` if available, which is the closest you can come to variable-length arrays with C90
- choose a maximum buffer size which is always used and fail if the given `limit` argument overflows
As a side note, even though C99 allows variable-length arrays, it's still illegal to use the value of an integer variable with static storage duration as size for an array with static storage duration, regardless of `const`-qualification: While there's nothing which prevents this in principle if the integer variable is initialized in the same translation unit, you'd have to special-case variables with visible defintion from those whose definition resides in a different translation unit and would either have to disallow tentative defintions or require multiple compilation passes as the initialization value of a tentatively defined variable isn't known until the whole translation unit has been parsed.
Problem
I'm dynamically calculating the size of an array. Something like: ``` void foo(size_t limit) { char buffer[limit * 14 + 1]; } ``` But just GCC compiler says: ``` error: ISO C90 forbids variable length array ‘buffer’ ``` searching on SO I found this answer: C99 §6.7.5.2: If the size is an expression that is not an integer constant expression... ...each time it is evaluated it shall have a value greater than zero. So, I did the re-declaration of size limit type variable to: ``` void foo(const size_t limit) ``` But it continues to give warning for me. Is this a GCC bug?