fclose and mem leack problem.

**apacz** · 09-18-2006

Hello.
I have such a code:

Code:

FILE *plik;
        if(argc > 1)
                plik = fopen(argv[1], "r");
        if(argc <= 1 || plik == NULL)
        {
                plik = stdin;
        }

and now, can i just do fclose(plik) or i have to check if plik == stdin, and if not, then fclose(plik). Would it be something wrong to do fclose(plik) when plik=stdin ?

And i have also a question about mem leak in my program. I used valgrind to investigate it:

==13011==
==13011== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
==13011== malloc/free: in use at exit: 4096 bytes in 1 blocks.
==13011== malloc/free: 806 allocs, 805 frees, 35664 bytes allocated.
==13011== For counts of detected errors, rerun with: -v
==13011== searching for pointers to 1 not-freed blocks.
==13011== checked 1353972 bytes.
==13011==
==13011== 4096 bytes in 1 blocks are still reachable in loss record 1 of 1
==13011== at 0x3C034183: malloc (in /usr/local/lib/valgrind/vgpreload_memcheck.so)
==13011== by 0x3C108DAD: __smakebuf (in /lib/libc.so.5)
==13011== by 0x3C108D1D: __swsetup (in /lib/libc.so.5)
==13011== by 0x3C0FE606: __vfprintf (in /lib/libc.so.5)
==13011==
==13011== LEAK SUMMARY:
==13011== definitely lost: 0 bytes in 0 blocks.
==13011== possibly lost: 0 bytes in 0 blocks.
==13011== still reachable: 4096 bytes in 1 blocks.
==13011== suppressed: 0 bytes in 0 blocks.

So it seems there isn't a pointer losing but still, there is one more alloc than free. I suspect that this one more alloc is made by program, because my main() declaration looks like:

Code:

int main(int argc, char *argv[])

but do I have to free it somewhere or am i wrong ?
Regards,
apacz.

**ssharish2005** · 09-18-2006

It doesn't make to me any sense this code

Code:

FILE *plik;
        if(argc > 1)
                plik = fopen(argv[1], "r");
        if(argc <= 1 || plik == NULL)
        {
                plik = stdin;   // <-- you are overwritting the pointer which is actually pointing to the file
        }

The second If condition will be exceuted making the Plik pointer to be overwritten by the stdin (even thought plik is not null, that is because of OR logical operator)

ssharish2005

**apacz** · 09-18-2006

My program should be run like this: ./a.out file_name
and now - if someone did just "./a.out" then he can input data from keyboard. But if argc > 1 (so he put file name) we try to open this file for read. If something failed (then plik == NULL) then program autmatically switch to stdin.
Regards,
apacz.

**Salem** · 09-18-2006

> and now, can i just do fclose(plik) or i have to check if plik == stdin
Probably falls into the "should be OK, but better to check" categories.

> malloc/free: in use at exit: 4096 bytes in 1 blocks.
I'm guessing this was a buffer allocated the first time you called vfprintf(), in which case there isn't much you can do about it. The pointer to that memory is probably held in some static variable which you don't have access to.

**ssharish2005** · 09-18-2006

Originally Posted by apacz

My program should be run like this: ./a.out file_name
and now - if someone did just "./a.out" then he can input data from keyboard. But if argc > 1 (so he put file name) we try to open this file for read. If something failed (then plik == NULL) then program autmatically switch to stdin.
Regards,
apacz.

if that was your requirnment, the program would look something as follow

Code:

#include<stdio.h>

int main(int argc, char **argv)
{
    FILE *Ptr;
    char FileName[20];
    
    if(argc > 1)
    {
        Ptr = fopen(argv[1],"r");
    fclose(Ptr);
    }
    if((argc == 1) || Ptr == NULL)
    {
        Ptr = stdin;
        
        printf("Enter the file name\n?");
        fgets(FileName,20,Ptr);
 
        printf("Filename : %s",FileName);
    }

    getchar();
    return 0;
}
/*my output

C:\Documents and Settings\harish\Desktop\programs>testStdinPtr.exe
Enter the file name
?test.txt
Filename : test.txt


C:\Documents and Settings\harish\Desktop\programs>
*/

ssharish2005

**apacz** · 09-18-2006

Well, my intension was to get a data from a file if it was gave while running program ("./a.out filename" situation) or to get a data from keyboard. So if there was no filename while running a program ("./a.out" situation) i set plik = stdin, and then later i just do fscanf(plik, "...", ...); But what about fclose() on such a pointer (as in my first question) ?
Regards,
apacz.

**ssharish2005** · 09-18-2006

well, it is just the same code. did u find the difference in your code and my code

ssharish2005

**apacz** · 09-18-2006

Ok, thx. So there is nothing bad in fclose(ptr) when ptr == stdin ? Do you know maybe something about my mem leak problem?
Regards,
apacz.

**ssharish2005** · 09-18-2006

ohhh, sorry it isn't a good idea of closing Ptr when it is pointing to stdin. which means u closing the standard input pointer, where it stops u in reading any more char from the keyboard

ssharish2005

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fclose and mem leack problem.