What advantages does modern Fortran have over modern C++?

Question

I'm trying to decide between Fortran and C++ for an application in scientific computing. It's not clear to me if Fortran still has advantages over other languages when it comes to performance. For example, I believe since Fortran enforces strict aliasing, better optimizations could be made by the compiler when compared to C before C99. I'm unsure of how C++ fits in here.

Any guidance?

Solution 1

I took a look at some of the stuff in the latest Fortran standards, and frankly I'm impressed. A lot of what I hated about the language 20 years ago is gone now. No more line numbers and special columns (may they burn in hell).

Fortran has been heavily used in engineering circles for 50 years now. That gives you two advantages if you work in those circles. First off, these folks care a lot about optimization. That means Fortran compilers tend to have the best optimizers around. The language itself is a lot more optimizable than Cish languages too, thanks to its lack of aliasing.

The second advantage is that Fortran's library support for number crunching simply cannot be beat. The best code is nearly always going to be the well-debugged code you don't have to write.

If your application doesn't fall under scientific, engineering, or number crunching in general, then neither of the above will be a big deal for you, so you may be better off looking elsewhere.

Solution 2

The other major issue is the learning curve which is very huge for C++ and exceptionally small for Fortran (90 and later). Fortran is like MATLAB with operations like ...

• B'DB is matmul( matmul(transpose(B), D), B )
• L2 norm of a vector is norm2(x)
• SVD of a matrix using LAPACK is call gesvd(A,S,u,vt)

Fortran also has pointers, dynamic memory, user defined data types etc.

It is well supported by major vendors (Intel/Sun/IBM/Cray/PGI/NAG etc.), open source (gfortan/g95) communities and developers of numerical library/APIs such as PETSc, MPI etc.

Heck the new standard (Fortran 2008) even has co-arrays for doing parallel programming without the need for MPI/OpenMP and some Fortran compilers already support it (g95 and Cray).

Basically it has all the good qualities required for numerical computing, is easier than MATLAB, is standardized, free, scalable (with MPI/OpenMP and co-arrays), produces blazing fast/parallel code.

For numerics nothing beats Fortran but unfortunately for anything else everything beats Fortan. So if you are a scientist with a safe job and only do numerical/HPC computing then stick with Fortran otherwise learn and use C++ as it is widely used for non numerical software.

Solution 3

Fortran allows whole array operations and also operations on array sections. There are C++ classes for arrays, but I don't think you can refer to a slice such as x(:,2:,1:N3:2) as easily as in Fortran. This lets one express some algorithms pretty concisely.

The convenience of Fortran's array operations extends to arrays of derived types. Suppose you have a an array of dates:

type date
integer :: month,day,year
end type date

type(date) :: x(1000)

Then x refers to the array of dates, x%month refers to the array of months, and pack(x,x%month==1) refers to all dates in January. How many other programming languages offer this convenience?

Some of the earlier comments about Fortran -- "old and disgusting" -- are biased and should be discounted accordingly. Let me argue the opposite. In my opinion the free format of Fortran 90 looks better than the syntax of C and C++, with the curly braces and semicolons. Leaving them out or incorrectly putting them in can cause errors in C and C++ that have no counterpart in Fortran.

Solution 4

Fortran has been highly optimized for mathematical (especially matrix) like operations.

C++ has been highly optimized for object usage.

Which is more important to you.

As noted below C++ has an optimized matrix library.
But Fortran's whole purpose is optimization of mathematical processes (especially matrix operations). The fact that these optimizations are built into the foundation of the language (rather than a library) and have about a two decade head start on research over C++ I doubt (but don't know for a fact) that in this area Fortran is going to win hands down.

Solution 5

Advantages of fortran95 and above over c++(2003):

1. As previously(by user4562) mentioned short learning curve(my first language was C and i still can't master it , similar is true for C++)
2. (My personal opinion) Easy for code transition from Octave(for that matter Matlab)similar syntax,same modularity[I use Octave to prototype a program and rewrite in fortran95 for speed],though u can directly use octave code in C++.
3. dynamic memory allocation is quite straight forward.(f77 didn't have this at all!)
4. libraries support (u can do this in c++ as well , but its natural to use fortran)
5. Co-array support for parallel computing (pity only cray supports them as of feb 2011 gfortran work has started as of gfortran4.6 but still a long way to go)

in short if your program or application is purely scientific computation use fortran 95 and above if calculating a few numbers is just part of the story use C++ (or whatever u feel is better)

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