localtime vs localtime_s and appropriate input arguments

Question

time_t rawtime;
struct tm * timeinfo;
time ( &rawtime );
timeinfo = localtime ( &rawtime );

This returns: warning C4996: \'localtime\': Thi

Answer 1

localtime_s is just a microsoft implementation of the localtime functon, you can safely keep using locatime becaue it's C++ ISO compliant and ony microsoft marked it as "deprecated". The localtime function itself isn't deprecated at all in the C++ world.

The localtime_s reference says that these parameters should be passed to it:

_tm 
Pointer to the time structure to be filled in.
 time 
Pointer to the stored time.

Answer 2

localtime returns a pointer to a statically allocated struct tm.

With localtime_s, you pass in a pointer to a struct tm, and localtime_s writes its result data into that, so your code would change from:

struct tm *timeinfo;
timeinfo = localtime(&rawtime);

to something like:

struct tm timeinfo;
localtime_s(&timeinfo, &rawtime);

This way, it's writing to your buffer instead of having a buffer of its own.

Answer 3

As Lightness Races in Orbit pointed out, localtime is not thread safe as well as several other time function. I wanted to know more about the subject and I found a relevant blog post with a thoughrough explanation about that.

The quote below explains why localtimeis not thread-safe:

[...] localtime returns a pointer to a static buffer (std::tm*). Another thread can call the function and the static buffer could be overwritten before the first thread has finished reading the content of the struct std::tm*.