Category on NSDate to print timestamp in ISO-8601 format.

iso_8601_category.m

#import <Foundation/Foundation.h>

@interface NSDate (ISO8601)
- (NSString *)mdx_canonicalTimestamp;
@end

@implementation NSDate (ISO8601)

- (NSString *)mdx_canonicalTimestamp
{
    static NSISO8601DateFormatter* formatter;
    static dispatch_once_t onceToken;
    
    dispatch_once(&onceToken, ^{
        formatter = [[NSISO8601DateFormatter alloc] init];
        formatter.formatOptions = NSISO8601DateFormatWithInternetDateTime;
    });
    
    return [formatter stringFromDate:self];
}

@end

int main(int argc, char *argv[]) {
    @autoreleasepool {
        NSDate* now = [NSDate date];
        NSLog(@"%@", [now mdx_canonicalTimestamp]);
    }
}