Fortran programming style

Shenren_CN · January 25, 2011, 21:33

Hi,

I'm new to writing CFD code in Fortran. I saw two different styles in writing code in Fortran lately and have been wondering what's the pros and cons of both.

One of them uses global variables substantially, and when a subroutine is called, there's normally no parameters pass; the other uses local variables, and every time a subroutine is called, a long list of parameters are passed, which is giving me trouble in easily keeping track of the variables being passed and used.

Intuitively, I think the 1st approach is better, apparently more readable. I wonder what's your opinion on this, and any suggestion on which style I should adopt when I write my code.

Cheers,
SX

DoHander · January 25, 2011, 21:38

If you want to be able to parallelize your code at a later time, you will avoid the use of global variables.

(personal opinion of course)

Do

Shenren_CN · January 26, 2011, 05:24

Quote:

Originally Posted by DoHander

If you want to be able to parallelize your code at a later time, you will avoid the use of global variables.

(personal opinion of course)

Do

Thanks DoHander,
Could you please elaborate a little bit on this? Since I don't know anything about parallelization yet, why would global variables cause trouble for doing that?

Regards,
SX

ztdep · January 31, 2011, 09:53

for large cfd procedure, do not use global variable heaviley.
feel free to use class, and subroutine to exchange infromation.
look like a black box to other people

Rami · February 1, 2011, 10:08

Hello Shenren Xu,

Another reason to avoid global variables is they make code debugging difficult, as when some variable changes, it is difficult to trace where it was changed.

Rami

hadian · February 3, 2011, 00:00

though passing variables to a subroutine by its argument is more recommended by programmers ( and i like it more), but the code run faster when you use global variables. In C family languages the pointer targeting the first member of a array in passed to a function, but if FORTRAN other information is passed and this can slow down the code. Moreover, the memory of the system should be considered too. when you use local variables, you will use extra memory for those variables when the sub-program is running.

Mich · February 4, 2011, 07:57

Arrays and variables which don't change in "main loop", it is possible to make global. For example, grid nodes.

January 25, 2011, 21:33	Fortran programming style	#1
Shenren_CN Member Shenren Xu Join Date: Jan 2011 Location: London, U.K. Posts: 67 Rep Power: 15	Hi, I'm new to writing CFD code in Fortran. I saw two different styles in writing code in Fortran lately and have been wondering what's the pros and cons of both. One of them uses global variables substantially, and when a subroutine is called, there's normally no parameters pass; the other uses local variables, and every time a subroutine is called, a long list of parameters are passed, which is giving me trouble in easily keeping track of the variables being passed and used. Intuitively, I think the 1st approach is better, apparently more readable. I wonder what's your opinion on this, and any suggestion on which style I should adopt when I write my code. Cheers, SX

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January 25, 2011, 21:38		#2
DoHander Senior Member Join Date: Nov 2009 Posts: 411 Rep Power: 20	If you want to be able to parallelize your code at a later time, you will avoid the use of global variables. (personal opinion of course) Do

January 31, 2011, 09:53		#4
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	for large cfd procedure, do not use global variable heaviley. feel free to use class, and subroutine to exchange infromation. look like a black box to other people

February 1, 2011, 10:08		#5
Rami Senior Member Rami Ben-Zvi Join Date: Mar 2009 Posts: 155 Rep Power: 17	Hello Shenren Xu, Another reason to avoid global variables is they make code debugging difficult, as when some variable changes, it is difficult to trace where it was changed. Rami

February 3, 2011, 00:00		#6
hadian Member Mohammad Reza Hadian Join Date: Mar 2009 Location: Yazd, Iran Posts: 52 Rep Power: 17	though passing variables to a subroutine by its argument is more recommended by programmers ( and i like it more), but the code run faster when you use global variables. In C family languages the pointer targeting the first member of a array in passed to a function, but if FORTRAN other information is passed and this can slow down the code. Moreover, the memory of the system should be considered too. when you use local variables, you will use extra memory for those variables when the sub-program is running.

February 4, 2011, 07:57		#7
Mich New Member lpk Join Date: Apr 2009 Posts: 2 Rep Power: 0	Arrays and variables which don't change in "main loop", it is possible to make global. For example, grid nodes.