fscanf won't work for long files

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  1. #1
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    fscanf won't work for long files

    Hello I'm having problems using fscanf. I'm using it to read data from a file into an array and for short files it works fine i.e. with about 12 bits of data but now I have a file with say 200 bits of data and this just causes the program to crash does anyone know what I'm doing wrong please. I've included a copy of the program below followed by the data from one of the long files I'm trying to read.

    Code:
    #include <stdio.h>
    #include <math.h>
    
    char file[10];
    
    FILE *data;
    
    int main ()
    
    
    {
            {
                do
                {
                printf ("Type in the name of the data file: ");
                scanf ("%s", &file);
    
                //Open file
    
                data = fopen(file, "r");
    
                if (data == NULL)
                printf("\n ERROR - Cannot open the designated file \n") ;
    
                }
                while (data==NULL);
    
            }
    
        int count;
        int count1;
        float a[count];
    
        count=0;
    
                while(!feof(data)) {
                fscanf(data,"%f", &a[count]);
                count++;}
    
            // Test to print values from file
            for(count1=0; count1<count-1; count1++)
            printf("Is = %f\n", a[count1]);
    }
    File

    0
    0.381
    0.584
    0.813
    0.991
    1.067
    1.219
    1.448
    1.651
    1.677
    1.372
    0.965
    0.711
    0.508
    0.457
    0.508
    0.483
    0.127
    -0.482
    -0.965
    -1.295
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    -13.513
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    -13.386
    -13.259
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  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
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    The edge of the known universe
    Posts
    32,855
    > float a[count];
    This does NOT create an array which magically expands as you increase the value of count.

    All that you're getting is an array whose size is based on the uninitialised value of count (at the point you declare the array).

    Investigate the use of malloc and possibly realloc to create space you can extend at run-time.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    Kernel hacker
    Join Date
    Jul 2007
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    Farncombe, Surrey, England
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    Or, if you don't really care about saving every single byte possible, guess on a huge number that your file won't exceed - say 10000 - and create an array of that size. Just make sure that you do fail gracefully if the file happens to be bigger.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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