The difference between localtime and Localtime_r

Turn from: http://blog.csdn.net/maocl1983/article/details/6221810#include <cstdlib>#include<iostream>#include<time.h>#include<stdio.h>using namespacestd;intMainintargcChar*argv[]) {time_t Tnow=Time (NULL); time_t tEnd= Tnow +1800; //Note the difference between the following two lines    structtm* PTM = localtime (&Tnow); structtm* ptmend = localtime (&tEnd); Charsztmp[ -] = {0}; Strftime (Sztmp, -,"%h:%m:%s", PTM); Charszend[ -] = {0}; Strftime (Szend, -,"%h:%m:%s", Ptmend); printf ("%s/n", sztmp); printf ("%s/n", Szend); System ("PAUSE"); returnexit_success;} The final result is: +: -: the  +: -: theInconsistent with the original idea. Check the localtime documentation to find this passage: this structure isStatically allocated and shared by the functions Gmtime and localtime. Each time either one of these functions isCalled the content of ThisStructure isoverwritten. That means you can only use the localtime () function once at a time, or it will be rewritten! The localtime () function need not be reentrant. A function that isNot required to be reentrant isNot required to is thread-safe. So localtime () is not reentrant. At the same time LIBC provides a reentrant version of the function Localtime_r (); unlike localtime (), the reentrant version isNot required toSetTzname. Modify Program: #include<cstdlib>#include<iostream>#include<time.h>#include<stdio.h>using namespacestd;intMainintargcChar*argv[]) {time_t Tnow=Time (NULL); time_t tEnd= Tnow +1800; //Modify the program here//struct tm* ptm = localtime (&tnow); //struct tm* ptmend = localtime (&tend);    structTM PTM = {0 }; structTM Ptmend = {0 }; Localtime_r (&tnow, &PTM); Localtime_r (&tend, &ptmend); Charsztmp[ -] = {0}; Strftime (Sztmp, -,"%h:%m:%s",&PTM); Charszend[ -] = {0}; Strftime (Szend, -,"%h:%m:%s",&ptmend); printf ("%s/n", sztmp); printf ("%s/n", Szend); System ("PAUSE"); returnexit_success;} The final result is:Ten: in: .  Ten: -: .  

The difference between localtime and Localtime_r