Question

I would like to read a file that has the sample number, values and status(1.1, 23,0). I used a Struct to hold that information. I will pass the function struct array and the file location.

#include <stdio.h>

struct Data_point
{
    long sampleNumber;
    double value;
    int status;
};


int filldata(struct Data_point *a, const char *filelocation)
{
    FILE *f;
    if((f=fopen(filelocation,"r"))==NULL)
    {
        printf("You cannot open");
    }
    fscanf(f, "%ld%lf%d", a.sampleNumber, a.value, a.status);
}



int main(void)
{
    struct Data_point data[10];
    filldata(data, "/home/alexchan/IntrotoC/rec11/dataPoints.txt");
    return 0;
}

But, I got an error saying, “request for member not a structure”…

Answer 1

One problem is that the filldata() is taking a pointer argument. So you use -> to address members not “.”. So a.sampleNumber should be a->sampleNumber for example.

Another issue is that filldata() is reading in a single struct, but you are passing it the pointer to the top of the array, which is synonymous with &(data[0]). So this function will just overwrite that first element if you call it repeatedly (which you didn’t). If you call it in a loop you will need to pass it in pointers to the individual array members:

for(int i = 0; i < 10; ++i){
filldata(&(data[i]), "/home/alexchan/IntrotoC/rec11/dataPoints.txt");
}

You could actually use data + i as the first arg instead of &(data[i]) but I like the latter as I find it more readable.