A strlen detail that is easily overlooked

Today, I saw a problem with the length of an array in csdn. I felt pretty good. I just summarized it and recorded it.

Char test [] = {0x01,0x02,0x03 };

Int A = strlen (test );

Int B = sizeof (test );

The A value is an uncertain value, because strlen determines that the string ends when the pointer goes to the address with the value '\ 000, '\ 000' indicates 0x00 in hexadecimal notation. The value B is 3, and sizeof is the memory occupied by the returned variables.
If chartest [] = {0x01,0x00,0x03}; then a = 1 because 0x00 is the string Terminator. B is still 3.

If chartest [20] = {0x01,0x02,0x03}; then a = 3 is initialized as 0x00 for the last 17 values. B is 20.

If chartest [20] = {0x01,0x00,0x03}; then a = 1. B = 20. The principle is as follows.