c++ string "%02d:%02d:%02d:%06ld", timenow->tm_hour, timenow->tm_min, timenow->tm_sec, time.tv_usec

This is a C string that uses format specifiers to construct a message that includes the current time. The format specifiers are:

- `%d`: integer decimal format
- `%ld`: long integer decimal format

The message format is:

`"\x02d:\x02d:\x02d:\x06ld"`

- `\x02`: represents the ASCII control character STX (start of text), which is equivalent to character 2.
- `\x06`: represents the ASCII control character ACK (acknowledge), which is equivalent to character 6.

When the string is printed, the format specifiers will be replaced with the corresponding values provided as arguments. `timenow->tm_hour`, `timenow->tm_min`, and `timenow->tm_sec` are integers representing the current hour, minute, and second, respectively. `time.tv_usec` is a long integer representing the current microsecond.

For example, if the current time is 01:23:45.678910, the string would be printed as:

`"\x021:\x023:\x024:\x06678910"`