查看NSCharacterSet的字符集

NSCharacterSet *charset = NSCharacterSet.URLQueryAllowedCharacterSet;
NSMutableArray *array = [NSMutableArray array];
for (int plane = 0; plane <= 16; plane++) {
    if ([charset hasMemberInPlane:plane]) {
        UTF32Char c;
        for (c = plane << 16; c < (plane+1) << 16; c++) {
            if ([charset longCharacterIsMember:c]) {
                UTF32Char c1 = OSSwapHostToLittleInt32(c); // To make it byte-order safe
                NSString *s = [[NSString alloc] initWithBytes:&c1 length:4 encoding:NSUTF32LittleEndianStringEncoding];
                [array addObject:s];
            }
        }
    }
}
NSLog(@"%@", [array componentsJoinedByString:@""]);

NSCharacterSet (NSURLUtilities) 的字符集内容

URLUserAllowedCharacterSet  
!$&'()*+,-.0123456789;=ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~

URLPasswordAllowedCharacterSet
!$&'()*+,-.0123456789;=ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~

URLHostAllowedCharacterSet
!$&'()*+,-.0123456789:;=ABCDEFGHIJKLMNOPQRSTUVWXYZ[]_abcdefghijklmnopqrstuvwxyz~

URLPathAllowedCharacterSet
!$&'()*+,-./0123456789:=@ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~

URLQueryAllowedCharacterSet
!$&'()*+,-./0123456789:;=?@ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~

URLFragmentAllowedCharacterSet
!$&'()*+,-./0123456789:;=?@ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~

Note: 上述的字符集中和网上其他博客提供的出入相当大，实际使用中被网上几乎所有的博客给坑了，特此记录下