Question

I know that I’m not supposed to do this in C90, and it’s a rather basic stuff.

char name[strlen(s)];

ArrayLength.c:11: warning: ISO C90 forbids variable length array ‘name’

Did they want me to specifically use malloc? I’m just curios here about the logic behind it.

Answer 1

It’s forbidden because C90 doesn’t support variable-length arrays (VLAs). It’s really as simple as that.

Your options are:

• Declare a fixed-length array that can cope with the maximum string length you want to work with.
• Dynamically-allocate the array (using malloc).
• Work with a compiler that offers VLAs a non-standard language extension, e.g. GCC. (I don’t recommend this, because it means you’ll end up writing non-portable code.)
• Use C99 instead, where VLAs are supported. Note that VLAs are allocated on the stack, which can cause all sorts of issues if you run out of stack space (unlike with malloc, there’s no concept of being able to check that the allocation was successful).

[Note: If you’re allocating an array in order to make a copy of s, you’ll need to use strlen(s)+1 as the size (remember the null terminator).]