A sequence of calls to strtok split str into tokens.
A token is a character sequence separated by a single character
delimiter that is part of the string set.
On the first call str is a non-NULL string pointer whose
first character is used as the starting location to scan for
The strtok function begins searching the string str
for the first delimiter character that is part of set. This
end of the token is automatically replaced by a null-character
by the function, and the beginning of the token is returned by
the function. The end location is a saved pointer for subsequent
In subsequent calls, when str is a NULL pointer, the
strtok function searches from the saved pointer and uses
therefore position right after the end of last token as the new
starting location for scanning. The token delimiters pointed to by
set may be different from call to call.