does eeprom_write_block function of avr.eeprom.h writes a NULL terminated string or we have to manually null terminate it

Question

http://www.nongnu.org/avr-libc/user-manual/group__avr__eeprom.html

I am trying to figure out that if we use eeprom_write_block function or eeprom_update_block function do we need to manually null terminate it?

I came across this tutorial on avr-freaks where in one comment it is said that you have to read the strings and null terminate them but there is no word about writing. Couldnt get anything the avr-libc manual as well.

UPDATE

I have reserved some parts of eeprom using EEMEM and they are strings. I am not sure how long the string would be except that it would be smaller than a max value. Now When I would read the string back from the eeprom I would just be reading the maximum number of bytes as again I would have no idea of the size of the string. If the eeprom has a null value at the end of the string when writing to it, the read string will have that null at the correct place.

Situation

I am saving mobile numbers of users as:

uint8_t EEMEM users[numberOfUsers][maxChar4Number];

Now when I get a number parsed and then save it to eeprom

#define eepu(message, EEADDR, BLKSIZE) eeprom_update_block((const void *)message, (void *)EEADDR, BLKSIZE);

eepu(user, users[0], strlen(user)); //strlen(user) will be less than the maxChar4Number

This will write the number to eeprom. When I read the i would be reading maxChar4Number bytes and a number could have been shorter than that length.

Answer 1

If you write a block which happens to be null-terminated, then reading it back should be fine. I do that when I want to save a filename in EEPROM. Just declare a suitable length (allowing room for the null terminator) and write the entire block to EEPROM.

Answer 2

Since one normally does not know how long a character string is, we need a way to convey this information. One technique used to avoid confusion is to add a NULL character (which is a zero) to the end of the string. Another is to explicitly state how long the string is.

In the case of the function eeprom_write_block() talked about here, we see that we are formally passing not only a pointer to the string but also the size of the string.