NSString表示的时间转为time_t

 1 time_t convertTimeStamp(NSString *stringTime)
 2 {
 3     time_t createdAt;
 4     struct tm created;
 5     time_t now;
 6     time(&now);
 7     
 8     if (stringTime) {
 9         if (strptime([stringTime UTF8String], "%a %b %d %H:%M:%S %z %Y", &created) == NULL) {
10             strptime([stringTime UTF8String], "%a, %d %b %Y %H:%M:%S %z", &created);
11         }
12         createdAt = mktime(&created);
13     }
14     return createdAt;
15 }