vsnprintf will try size of 5
n is: 68
 double size from to 10
vsnprintf will try size of 10
n is: 68
 double size from to 20
vsnprintf will try size of 20
n is: 68
 double size from to 40
vsnprintf will try size of 40
n is: 68
 double size from to 80
vsnprintf will try size of 80
n is: 68
vsnprintf successful print with size = 80 and return n= 68 the value=[a really long string is coming here and we want to see what happens!]
vsnprintf will try size of 5
n is: 68
 double size from to 10
vsnprintf will try size of 10
n is: 6
vsnprintf successful print with size = 10 and return n= 6 the value=[(null)]