Assign Text File Input to Array of Doubles

Question

So I'm reading values from a file delimited by a comma and assigning it to a 1D array of doubles. Here is the method I'm using to accomplish this:

double* readFile(char *fileName)
{
FILE *fp = fopen(fileName, "r");
char *token;
int i = 0;
int j = 0;

double *retval = (double *)malloc(5000 * sizeof(double));
if(fp != NULL)
{
    char line[10];
    while(fgets(line, sizeof line, fp) != NULL)
    {   
        //printf("Parsed line: %s\n", line);
        token = strtok(line, ",");           
        while(token != NULL)
        {
            printf("token: %s\n", token); 
            *retval = atof(token);
            printf("value: %d\n",*retval); 
            retval++; 
            token=strtok(NULL,",");
        }
    }
    fclose(fp);
} else {
    perror(fileName);
}

for(j = 0; j < i; j++)
{
    retval--; 
}

return retval;    
}

The problem I'm getting is that after I assign the atof() of the tokenized value, which is correct, the value that is saved in the pointer is absolutely incorrect. For instance, I have a textfile which is just all zeros, and whats being saved in the array is crazy values like -1587604999 in every single position.

Anyone see the problem?

D Krueger · Accepted Answer · 2014-12-04 01:37:47Z

1

You're using the %d format specifier for a double. You should try %f.

answered Dec 4, 2014 at 1:37

D Krueger

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Comments

Dinesh · Accepted Answer · 2014-12-04 01:38:29Z

1

retval has advanced and is now pointing to the next usable location.

You want to save the original malloc value and return that.

There might be other issues too, for example how does the caller know where the values end? Also, what if you get more than 5000 values? Also, free memory on error. But I assume this is merely your test code and you will eventually address these things.

answered Dec 4, 2014 at 1:38

Dinesh

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6 Comments

Scott James Walter Over a year ago

It is some test code, but these are important things to consider none the less. The caller will advance through the location in memory the same way I am right now in this method. That should work, correct?

Dinesh Over a year ago

Not with retval advanced the way it is being done currently. What you want to return to caller is the head of the array not the tail.

Scott James Walter Over a year ago

I just added something that should fix that, is there a more clever way or will this be sufficient?

Dinesh Over a year ago

You could towards the top end of code (1) double* array_head = retval; after the alloc, and at bottom (2) return array_head; You will not need the for loop

Dinesh Over a year ago

And I am also mildly curious if my answer actually helped fix your problem :)

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