Question

I wrote this basic function :

int save_files(PCHAR fileName)
 {
     errno_t         err;
     FILE*           pFile    =    NULL;

do
{
    if (!fileName)
    {
        printf("Input is NULL \n");
        break;
    }


    err = fopen_s( &pFile, fileName, "r");
    if(0 != err)
    {
        printf("The file %s was not opened for reading\n", fileName);
    }
    else
    {
       printf("The file %s was opened for reading \n", fileName);
    }

    /*getting the fileSize */
    fileSize    =   dbg_getFileSize(pFile);
    printf("############# FILE SIZE IS :  %d #############\n" );
 }

this is the function get file size :

UINT32 dbg_getFileSize(FILE *file)
 {
        UINT32  size = 0 ;

         if (file == NULL)
            {

            return -1;
             }

         fseek(file , 0L , SEEK_END);
         size = ftell(file);
         fseek(file, 0L, SEEK_SET);/*set it to the head!!! */

         return size;

     }

I open the same path all the time , and get different size every time
I tried opening it with “r” and “rb” , but still getting the same different numbers..

Answer 1

You get different file sizes because the following line:

printf("############# FILE SIZE IS :  %d #############\n" );

doesn’t actually specify the variable you’re trying to print. Hence it’s probably getting whatever rubbish is on the stack when you call it (I say probably, but anything could happen given that you’ve invoked the dreaded “undefined behaviour” ^(a)).

You might want to try this instead:

printf("############# FILE SIZE IS :  %d #############\n", fileSize );

---

^(a) From C99 7.19.6.1 The fprintf function, unchanged in C11 7.20.6.1, the equivalent section:

The fprintf function writes output to the stream pointed to by stream, under control
of the string pointed to by format that specifies how subsequent arguments are
converted for output. If there are insufficient arguments for the format, the behavior is
undefined. If the format is exhausted while arguments remain, the excess arguments are
evaluated (as always) but are otherwise ignored. The fprintf function returns when
the end of the format string is encountered.