Re: fscanf hangs

From:
 James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++,comp.lang.c,comp.os.ms-windows.programmer.tools.misc,comp.os.ms-windows.programmer.tools.mfc
Date:
Mon, 18 Jun 2007 08:36:37 -0000
Message-ID:
<1182155797.596257.311650@k79g2000hse.googlegroups.com>
On Jun 18, 3:19 am, PeterOut <MajorSetb...@excite.com> 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.


The code would be a lot easier to understand (and a lot safer)
if you'd use ifstream instead of fscanf. However...

ReadFile(char *csFileName)
{
        float fFloat1, fFloat2;
        long lLong1, lLong2, lNum, lLastX = iColumns-1, lLastY =iR=

ows-1;

        int iRead;
                FILE *fpInFile;

                if ((fpInFile= fopen(csFileName, "r")) == NULL) ret=

urn

ErrorOpeningFile(csFileName);

        do
        {
                                // It randomly hangs on the followinf
line
                iRead=fscanf(fpInFile, "%d%d%f%f%d", &lLong1, &lLong2, =

&fFloat1,

&fFloat2, &lNum);


As others have pointed out, you need %ld to be correct. If this
doesn't cause problems immediately, it's because by pure chance,
longs and ints have the same size on your implementation.

                if (iRead==0 || iRead==EOF) break;


And what is fscanf supposed to return in the case of:
    "1 2 3x 4.5 6"
?

Personally, I'd probably impose that each data set be on a
separate line, and do something like:

    std::string line ;
    int lineNo = 0 ;
    while ( std::getline( input, line ) ) {
        ++ lineNo ;
        std::istringstream s( line ) ;
        s >> long1 >> long2 >> float1 >> float2 >> num >> std::ws ;
        if ( ! s || s.get() != EOF ) {
            std::cerr << "Syntax error in line "
                      << lineNo
                      << ", ignoring it"
                      << std::endl ;
        } else {
            // ...
        }
    }

From your code, it's also not too clear where the lX and lY come

from, or how they evolve to handle your end conditions.
Normally, written correctly, using std::vector, you should be
able to automatically scale any arrays to the amount of data
read.

        } 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.


How would that change anything?

--
James Kanze (GABI Software, from CAI) email:james.kanze@gmail.com
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