Channel 9 Forums - Tech Off - C Standard Library string.h question involving strtok()

Tech Off - C Standard Library string.h question involving strtok()

Shining Arcanine — Sat, 08 Mar 2008 03:20:07 GMT

I know that strtok() is not thread safe, so I am wondering, does it return a memory location to which it keeps a static pointer or does it keep no pointer to the memory location it returns?

I guess what I am really asking is, will I be generating garbage if I do not explicitly free the pointer it returns?

Typically, I would think that answer would be yes, but since strtok() is not threadsafe, that might not be the case.

Tech Off - C Standard Library string.h question involving strtok()

JChung2006 — Sat, 08 Mar 2008 03:54:18 GMT

You shouldn't be freeing the pointer strtok returns at all.

Tech Off - C Standard Library string.h question involving strtok()

TimP — Sat, 08 Mar 2008 03:56:07 GMT

strtok uses a static pointer to keep track of where it is, that's why it's not thread safe. I took a look at the source code (strtok is only a handful of lines long, /glibc-2.7/string/strtok.c in the tarball) and it seems to only manipulate pointers pointing to your original string, so there's no need to free anything it returns. Just free the buffer the string was in at the end if it was dynamically allocated.

Tech Off - C Standard Library string.h question involving strtok()

Axel Rietschin — Sat, 08 Mar 2008 13:56:20 GMT

strtok_s() stores the context pointer on your side.