Question

help with file opening /closing

Asked by: avizit

I have two functions A and B ,

A(){
     ....
     B();
     .....
}


B(){
   write some date to logfile.txt;

}

-------------------------
function B is called from function A, now in B i need to write some data to a file , say logfile.txt
now for some reason , I am not allowed to open the logfile  in either the main function or function A.  So I have these following options

1. open/close  the file in B()   in which case I will end up opening/closing the file each time B() is called

2. create the File* fp as a static variable  , so i can open it once and then each time check if its null like this
B(){
  static FILE *fp = NULL;
  if( !fp){  
    fp = fopen(....) ;
 }
 do stuff with fp ;
 .....

}


In this case , I would not know when to close the file .

------------------------

Do you guys have any other way ?

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Asked On
2005-04-08 at 00:31:12ID21381224
Tags

file

,

close

,

fopen

,

open

Topic

C Programming Language

Participating Experts
3
Points
300
Comments
8

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Answers

 

by: sunnycoderPosted on 2005-04-08 at 01:09:54ID: 13734031

Hi avizit,

Way 2 is the way to go.
Other options would be to use global variables which is not a good idea ...
It would be interesting to know of contraints which would not allow you to open the file in A()

Cheers!
sunnycoder

 

by: avizitPosted on 2005-04-08 at 01:24:12ID: 13734094

>>It would be interesting to know of contraints which would not allow you to open the file in A()

the reason is ,
The call to B() in A() , is not a normal function call as in I don't insert call it explicitly. But I am modifying the interemediate code of the compiled program and inserting a call instruction [ which is a call to B() ]

the process is something like this

A() is in file fileA.c , and B() is in fileB.c
intially in A() there is no call to B() ,

while compiling fileA.c , the compiler inserts a call to B().
and later I link both the compiled object files.  B() is basically a logging function , which I may decide to change to do nothing , so i want everything to do with file pointers to be done in B() itself, otherwise there will be filepointer related junk on A() which may be totally unnecessary.


Hope I confused you enough :)

-------
am leaving this question open for a few days , to see if ppl have other techniques .

Thanks,
abhijit

 

by: sunnycoderPosted on 2005-04-08 at 02:32:55ID: 13734403

I got your point ... unless you could modify main, there would not be much sense in opening and closing in A either. ... your way 2 looks appealing to me

 

by: PaulCaswellPosted on 2005-04-08 at 03:12:22ID: 13734577

You have the right method but, to close the file, use 'atexit'.

You have several options:

1. Make the file handle a global to the 'B' module or use some system-specific method of discovering the file handle from the file name.

2. Add a perameter to 'B' that indicates that it should close the file.

Paul

 

by: NovaDenizenPosted on 2005-04-08 at 08:27:41ID: 13737256

Use a kind of instance pattern.

static FILE *logfileptr = NULL;
FILE *getLogFilePtr() {
    if (logfileptr == NULL) {
        logfileptr = fopen("logfilename", "wa");
    }
    return logfileptr;
}

Then, in B, just call getLogFilePtr() to get the pointer.  This way can be used in multiple B-like functions.

 

by: avizitPosted on 2005-04-10 at 07:51:21ID: 13747410

oops i meant to accept nova denizen .. .. sorry ..

 

by: sunnycoderPosted on 2005-04-10 at 21:26:54ID: 13750330

avizit,

Would you like me to reopen the question for you?

 

by: avizitPosted on 2005-04-10 at 21:54:51ID: 13750412

if no one objects i guess it doesn't really matter . i have awarded points as per what I wanted .
if anyone objects i am willing to undo my mistake .. but I hope its fine.

20120131-EE-VQP-002

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