Difference between unsigned char * and char *

The program defines the unsigned char * length. No, I want to ask why it should be defined as an unsigned char *. What is the difference between the unsigned char * and the data type defined by char? Generally, unsigned char * points to what data type, and char * points to what data type?

Unsigned char * is a data type pointing to unsigned char.
Char * is a data type pointing to the char type. All common characters can be seen that char * points to the string, while unsigned char * points to the hex.
In fact, there is no difference between them. Because no visible characters are negative.

 

There are actually differences, such as unsigned char test [] = {0xff}; printf ("% 02x", test [0]);

Char test [] = {0xff}; printf ("% 02x", test [0]); results are different. Differences between the unsigned number and the signed number