I am not a fan of the CRT, and don't use it in my libraries. However,
if you are programming in Windows, then Msvcrt.dll is present on your machine. It's not an "external" thing that the user has to buy and install, it's simply
there waiting to be used.
IMHO rolling your own is justified only if it improves your stuff: Can you reduce code size with an own routine? No, because a call to an existing function costs 6 bytes. Which leaves exactly one reason to reinvent the wheel:
speed