The syntax of strlen() function is
Note#1 : strlen(“”) differs from strlen(NULL)n=strlen(“”) , “” is a string containing null character.so,it returns the size as 0.n=strlen(NULL) gives undefined behavior because null is a constant and its not a string.
Note#2 : What happens to String Length if String is not terminated with null?UndefinedBehavior. printf will interpret “%s” as a standard C string. This means that the code that is generated will simply keep reading characters until it finds a null terminator (\0). This may eventually cross a memory boundary and cause an error or it may produce no output or crash or so on.