找不到strtok_s（）的文档

Question

What exactly is each argument passed to it, what does it return?

How exactly is it better than the regular strtok ?

Please give me the most simplified and basic explanation possible.

Answer 1

This is detailed in Appendix K (bounds checking interfaces) of the ISO C11 standard. This optional part of the standard provides "safer" ^(a) versions of already existing functionality provided in the core part of the standard.

The prototype is:

char *strtok_s (
    char * restrict        s1,
    rsize_t * restrict     s1max,
    const char * restrict  s2,
    char ** restrict       ptr);

The runtime constraints that are checked as part of the safety features are:

• The pointers s1max , s2 , and ptr must all be non-null.
• If s1 is a null pointer, then *ptr must not be.
• The value of *s1max must be less than or equal to RSIZE_MAX .
• The end of the token found must occur within the first *s1max characters of s1 for the first call
• The end of the token found must occur within the first *s1max characters of where searching resumes on subsequent calls.

The safety aspect is that, if any of those constraints are violated, no indirection occurs on s1 or s2 and no value is stored via ptr .

Other than those extra checks, it pretty much works identically to the standard strtok function, returning tokens from s1 separated by groups of delimiters found in s2 . I think the use of ptr makes it thread-safe since it using a non-static state provided by the user ^(b) .

---

^(a) Quoted because most parts of the standard are already safe if you know how to use them properly :-)

---

^(b) The one thing that's still missing is the ability to have empty tokens such as:

field1||||field5

Because strtok_s (and the original) treat |||| as a single separator, we have to find other ways to do this </rant> :-)