Streaming Security for the C Standard Library on OS X

Question

Is there a definitive list of features that are thread safe in the Mac OS X implementation in the C standard library?

There is a good answer here regarding glibc and f*() functions, but I have not found such a resource regarding OS X Is there such a thing?

For example, strptime() and strftime() thread safe? printf() ? These are the ones that may have internal buffers that I would not want to mess up. :)

Answer 1

The Single Unix specification provides a fairly short list of functions that may be unsafe (except that functions in the Legacy Feature Group may be unsafe even though they are not listed). The list includes strtok() , which Dave mentions in his answer, but does not include strptime() , not strftime() , not printf() .

https://stackoverflow.com/questions/664433/ ... claims that in response to a question that is pretty similar to this, OS X supports the above aspect of the specification, so I think this is probably the best list to use. (You will probably also be interested in the rest of this question, and in another answer to it, by the way.)

Answer 2

Any function that seems to have some magical ability to remember will most likely not be thread safe. Any function that returns a pointer that you do not expect free() is very often not thread safe.

Many of the functions you really need to worry about returning char* or struct foo* . Although this is not an ideal rule, it often points to a function that has some kind of static storage and is not thread safe.

strtok() is a simple example of is, and it succeeded in strtok_r() , which is thread safe. For many unsafe functions, there is function_r() (r for reentrant).