NSCalendar *calendar = [NSCalendar currentCalendar];
NSRange range =
[calendar rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit
forDate:[NSDate date]];
NSUInteger numberOfDaysInMonth =
range.length;
NSDate *datetime = [NSDate
dateWithTimeIntervalSince1970:csmcurrentTime-(86400*numberOfDaysInMonth *
data_current_index)];
NSDateFormatter *dateformat = [[[NSDateFormatter
alloc] init] autorelease];
[dateformat setDateFormat:@"yyyy年MM月"];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *comps = nil;
comps = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:mydate];
NSDateComponents *adcomps = [[NSDateComponents alloc] init];
[adcomps setYear:0];
[adcomps setMonth:-1];
[adcomps setDay:0];
NSDate *newdate = [calendar dateByAddingComponents:adcomps toDate:mydate options:0];