c++ - Why is vsnprintf safe? -

i have looked @ question these pdfs' 1 , 2, page , pretty understand happens if printf(some_test_string). not understand why ensuring size of buffer vsnprintf becomes safe compared vsprintf?

what happens in these 2 cases ?

case 1

char buf[3]; vsprint(buf, "%s", args); 

case 2

char buf[3]; vsnprint(buf, sizeof buf, "%s", args); 

in case 1, if string you're formatting has length of 3 or greater, have buffer overrun, vsprintf might write memory past storage of buf array, undefined behavior, possibly causing havoc/security concerns/crashes/etc.

in case 2. vsnprintf knows how big buffer contain result is, , make sure not go past that(instead truncating result fit within buf ).