buffer overflow - How do programs keep track of variable sizes?

[ad_1]

I am asking specifically for programs written in languages like javascript (node.js), python. What I wanna know is how do they defend against buffer overflows? I think almost all of their functions (that has something to do with memory) has statements like:

func copy(dst, src)
 if src.size > dst.size
 print "Can't copy"

What I wanna know is, how do these languages do src.size how do they keep track of the size?

[ad_2]

لینک منبع