The implementation shall not modify output in any way (e.g., by appending arbitrary newlines) apart from behavior expected from a standard printf-like function (e.g., replacing format specifiers).
Warning
Some implementations use size limited buffer for temporarily storing the log message.
Parameters
format
Pointer to a null-terminated byte string specifying how to interpret the data
...
Arguments specifying data to print
Returns
The number of characters printed (like printf), or a negative value on encoding/printing error.