Re: fscanf hangs

 James Kanze <>
Mon, 18 Jun 2007 08:36:37 -0000
On Jun 18, 3:19 am, 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.

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=


        int iRead;
                FILE *fpInFile;

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



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


&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

        } 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)
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