remove weird chars from char array ESP32

Question

When I'm converting a string to a char array there are always some weird chars at the end. I have to do it manualy because the convertTochar function crashes my ESP.

  String sssid = module.getCssid(); //String is stored in the eeporm
  char cssid[sssid.length()];
  Serial.println(sssid.length()); //prints correct length of 6
  //convert do ssid
  for( int i = 0; i<sizeof(cssid);i++){
    cssid[i] = sssid[i];
  }
  Serial.println(cssid); //prints myssid⸮?⸮2⸮?
enter code here

If I'm printing the value directly fromm eeprom there are no wired characters. Also the max eeprom size for the string is 10 bytes...

Why are these characters at the end of string?

Answer 1

You forgot to add one more character to the array to place a \0 (0 value byte) in. This denotes the end of a string. If you forget this, the string will continue until it finds the first 0 byte, which will probably be after the original string copy. This can be dangerous, because it might be in memory that is not containing useful data, and those weird character can be many if there is not a 0 soon or at all.

Note that the 6 bytes you get are the bytes EXCLUDING this 0 byte, so you need to allocate 7 bytes to store a string of length 6.

Instead of the for loop you can use the strcpy function which copies a function including the 0 string.

See description:

Description

The C library function char *strcpy(char *dest, const char *src) copies the string pointed to, by src to dest.

Declaration

Following is the declaration for strcpy() function. char *strcpy(char *dest, const char *src)

Parameters

dest − This is the pointer to the destination array where the content is to be copied.

src − This is the string to be copied.

Return Value

This returns a pointer to the destination string dest.

Example

The following example shows the usage of strcpy() function.

#include <stdio.h>
#include <string.h>

int main () {
   char src[40];
   char dest[100];

   memset(dest, '\0', sizeof(dest));
   strcpy(src, "This is tutorialspoint.com");
   strcpy(dest, src);

   printf("Final copied string : %s\n", dest);

   return(0);
}