How to memset char array with null terminating character?

Question

What is the correct and safest way to memset the whole character array with the null terminating character? I can list a few usages:

...
char* buffer = new char [ARRAY_LENGTH];

//Option 1:             memset( buffer, '\0', sizeof(buffer) );
//Option 2 before edit: memset( buffer, '\0', sizeof(char*) * ARRAY_LENGTH );
//Option 2 after edit:  memset( buffer, '\0', sizeof(char) * ARRAY_LENGTH );
//Option 3:             memset( buffer, '\0', ARRAY_LENGTH );
...

• Does any of these have significant advantage over other(s)?
  
• What kind of issues can I face with with usages 1, 2 or 3?
  
• What is the best way to handle this request?

Answer 1

Options one and two are just wrong. The first one uses the size of a pointer instead of the size of the array, so it probably won't write to the whole array. The second uses sizeof(char*) instead of sizeof(char) so it will write past the end of the array. Option 3 is okay. You could also use this

memset( buffer, '\0', sizeof(char)*ARRAY_LENGTH );

but sizeof(char) is guaranteed to be 1.