`alloca` is a simple addition to the stack pointer, so a single instruction, presuming it isn't folded into the normal bump of the stack pointer to allocate the fixed size local variables. There isn't really much cost to doing a dynamic stack allocation rather than a fixed one. Variable length arrays (VLAs) allow the same thing but can be slightly more portable.
Normal C caveats do apply here though: alloca is POSIX, not C (but is widely implemented outside of POSIX systems). VLAs are an optional standard feature. Neither is required to actually use the stack for storage.
Not sure if there are any platforms supported by curl which would prevent it's use of VLAs or alloca.
Normal C caveats do apply here though: alloca is POSIX, not C (but is widely implemented outside of POSIX systems). VLAs are an optional standard feature. Neither is required to actually use the stack for storage.
Not sure if there are any platforms supported by curl which would prevent it's use of VLAs or alloca.