如何使用gmtime和asctime删除警告C4996

Question

I have level 4 warning in my C++ project I want to solve it the warning is

Warning 1 warning C4996: 'gmtime': This function or variable may be unsafe. Consider using gmtime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

Warning 2 warning C4996: 'asctime': This function or variable may be unsafe. Consider using asctime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

code C++

time_t ltime;
time(&ltime);
tm* gmt = gmtime(&ltime);

char* asctime_remove_nl = asctime(gmt);

Answer 1

Below functions return pointers to static objects that may be overwritten by other subsequent calls(K&R Book). Hence they are not considered to be safe and due to this VS compiler would give the warning/error. It can be removed by adding the MACRO in the project(.proj file)(CRT_SECURE_NO_WARNINGS).

gmtime()
asctime()

However, we can write the small utility functions which would make the copy of these static strings.

// This would return the copy of time/date in std::string object to caller
std::string get_gmtime_asctime() {
 time_t ltime;
 time(&ltime);
 struct tm* gt = ::gmtime(&ltime);
 char* tmp = ::asctime(gt);
 std::string output(tmp);
 return output;
}

int main() {
    std::string out = get_gmtime_asctime();
    std::cout<<out<<std::endl;

}