[nonameiguess]

Much different from Python, though. As long as you compile your C program against the same version of libc you're running against, the program will still work, no matter how old the code. You just can't run a program that was compiled against an incompatible libc. A Python 2 interpreter can't run Python 3 code, and vice versa, no matter what, because the actual language changed.

[kazinator]

You can't always easily compile an old C program against the new C libraries you are running. Even if you can compile it, changes in libraries can break programs. E.g. say in the ancient library, memcpy with null pointer parameters worked, if the size was zero. The new library checks it and aborts. There are all sorts of issues like this.

Every time libraries and compilers advance, you're effectively porting all the existing code. You have to fix any build breakage, and re-validate everything.

Moreover, Python is a C program. Just get the old Python 2 C code and compile it against "the same version of libc you're running" and it will work, right? Where is the problem?

[josefx]

Why recompile it when the existing binary still works with the current runtime? At least on Linux the old version of memcpy will still be included in the runtime library to avoid this kind of issue.

[fnord123]

The point is that the code needs the runtime.