печать форматированного вывода (print formatted output)
Возвращаемое значение (Return value)
Upon successful completion, the dprintf(), fprintf(), and
printf() functions shall return the number of bytes transmitted.
Upon successful completion, the sprintf() function shall return
the number of bytes written to s, excluding the terminating null
byte.
Upon successful completion, the snprintf() function shall return
the number of bytes that would be written to s had n been
sufficiently large excluding the terminating null byte.
If an output error was encountered, these functions shall return
a negative value and set errno to indicate the error.
If the value of n is zero on a call to snprintf(), nothing shall
be written, the number of bytes that would have been written had
n been sufficiently large excluding the terminating null shall be
returned, and s may be a null pointer.
