Have you used any of the C++ interpreters (not compilers)?

Question

I am curious if anyone have used UnderC, Cint, Cling, Ch, or any other C++ interpreter and could share their experience.

Answer 1

NOTE: what follows is rather CINT specific, but given that its probably the most widely used C++ interpreter it may be valid for them all.

As a graduate student in particle physics who's used CINT extensively, I should warn you away. While it does "work", it is in the process of being phased out, and those who spend more than a year in particle physics typically learn to avoid it for a few reasons:

1. Because of its roots as a C interpretor, it fails to interpret some of the most critical components of C++. Templates, for example, don't always work, so you'll be discouraged from using things which make C++ so flexible and usable.

2. It is slower (by at least a factor of 5) than minimally optimized C++.

3. Debugging messages are much more cryptic than those produced by g++.

4. Scoping is inconsistent with compiled C++: it's quite common to see code of the form

   if (energy > 30) { 
       float correction = 2.4;
   }
   else {
       float correction = 6.3;
   }
   
   somevalue += correction; 
   

   whereas any working C++ compiler would complain that correcton has gone out of scope, CINT allows this. The result is that CINT code isn't really C++, just something that looks like it.

In short, CINT has none of the advantages of C++, and all the disadvantages plus some.

The fact that CINT is still used at all is likely more of a historical accident owing to its inclusion in the ROOT framework. Back when it was written (20 years ago), there was a real need for an interpreted language for interactive plotting / fitting. Now there are many packages which fill that role, many which have hundreds of active developers.

None of these are written in C++. Why? Quite simply, C++ is not meant to be interpreted. Static typing, for example, buys you great gains in optimization during compilation, but mostly serves to clutter and over-constrain your code if the computer is only allowed to see it at runtime. If you have the luxury of being able to use an interpreted language, learn Python or Ruby, the time it takes you to learn will be less than that you loose stumbling over CINT, even if you already know C++.

In my experience, the older researchers who work with ROOT (the package you must install to run CINT) end up compiling the ROOT libraries into normal C++ executables to avoid CINT. Those in the younger generation either follow this lead or use Python for scripting.

Incidentally, ROOT (and thus CINT) takes roughly half an hour to compile on a fairly modern computer, and will occasionally fail with newer versions of gcc. It's a package that served an important purpose many years ago, but now it's clearly showing it's age. Looking into the source code, you'll find hundreds of deprecated c-style casts, huge holes in type-safety, and heavy use of global variables.

If you're going to write C++, write C++ as it's meant to be written. If you absolutely must have a C++ interpretor, CINT is probably a good bet.