Re: fscanf hangs

From:

PeterOut <MajorSetback@excite.com>

Newsgroups:

comp.lang.c++,comp.lang.c

Date:

Mon, 25 Jun 2007 19:15:44 -0700

Message-ID:

<1182824144.784244.18500@k79g2000hse.googlegroups.com>

On Jun 23, 2:50 pm, Johan Bengtsson <qwerty...@hotmail.com> wrote:

PeterOut wrote:

I am using MS Visual C++ 6.0 on Windows XP 5.1 (SP2).

I am not sure if this is a C, C++ or MS issue but fscanf has been
randomly hanging on me. I make the call hundreds, if not thousands,
of times but it hangs in different places with the same data. The
offending code follows.

ReadFile(char *csFileName)
{
   float fFloat1, fFloat2;
   long lLong1, lLong2, lNum, lLastX = iColumns-1, lLastY =iRows-1;
   int iRead;
                FILE *fpInFile;

                if ((fpInFile= fopen(csFileName, "r")) == NULL) return
ErrorOpeningFile(csFileName);

   do
   {
                                // It randomly hangs on the followinf
line
           iRead=fscanf(fpInFile, "%d%d%f%f%d", &lLong1, &lLong2, &fFloat1,
&fFloat2, &lNum);
           if (iRead==0 || iRead==EOF) break;
   } while (lX < lLastX || lY < lLastY);
}

I am wondering if I should just do binary reading so as to have more
control over what is going on.

Many thanks in advance for any assistance,
Peter.

Hmmm, I was thinking that it might be a consequence of corrupt memory
(like buffer overruns, changing memory after free() (or equivalent) or
some other similar problem).
Test if you have access to a function called AfxCheckMemory(). (It is
available in later versions of their compiler, don't know if it is in
that version however).
If it is available try placing

ASSERT(AfxCheckMemory());

immediately before the call to fscanf(). If it breaks you have
previously overwritten some memory somewhere in your program where that
should not happen...- Hide quoted text -

- Show quoted text -

Hi Johan,

That looks likfe a handy function. Thanks for bringing it to my
attention. I put it in and it didn't flag anything. I have decided
to give up on fscanf and add the following code instead.

ERROR_NUMBER FReadLine(FILE *fpInputFile, char *csBuffer)
{
     int i;

     if ((csBuffer[0] = fgetc( fpInputFile )) == EOF) return
ERROR_READING_FILE;
     i = (csBuffer[0] == '\n')? 0 : 1;
     while ((csBuffer[i] = fgetc( fpInputFile )) != '\n')
     {
         if (csBuffer[i++] == EOF) return ERROR_READING_FILE;
     }
     csBuffer[i] = '\0';

     return ERROR_NONE;
}

if ((fpFile = fopen(csFileName, "r")) == NULL)
{
         // Error handling
}
{
    float fMean;
    long lX, lY, lLastX = fppPlane->iColumns-1, lLastY = fppPlane-

iRows-1;

char csBuffer[32];

    do
    {
        if ((enErrorNumber=FReadLine(fpFile, csBuffer))!=ERROR_NONE) break;
        lX=atoi(strtok(csBuffer, "\t"));
        lY=atoi(strtok(NULL, "\t"));
        fMean=(float)atof(strtok(NULL, "\t"));
    } while (lX < lLastX || lY < lLastY);
}
fclose(fpFile);

So far no problem.

Thanks again for your help,
Peter.