Reading a binary file with fread

Question

I am trying to read a bin with fread ? . The binary file I am reading has 1 million sets of data. However I am only getting 600+ and the data read is either 0 or -1.#QNAN0 . Am I using fread the right way?

struct Data {
    float time;
    float signal1;
    float signal2;
    float signal3;
};

long i;
static struct Data data[1000]; //(Solve by using static)

long openfile() {

  FILE *fp;
  char* filename = "Test_0012.bin";

  fp = fopen(filename, "rb");
  if (fp == NULL){
      printf("Could not open file %s",filename);
      return 1;
  }

  while(!feof(fp)){
    fread(&data, sizeof(data),1,fp);

    printf("%d\t", i);
    printf("%f\t", data[i].time);
    printf("%f\t", data[i].signal1);
    printf("%f\t", data[i].signal2);
    printf("%f\n", data[i].signal3);

    i++;
  }
  fclose(fp);
  return i;
}

Answer 1

You probably want something like this:

int i = 0;
do
{
  fread(&data[i], sizeof(struct Data), 1, fp);
} while (!feof(fp));

You want to read n times the size of struct Data , rather than once the whole array.

BTW you also need to check if there are no more than 1000 (which equals sizeof(data)/sizeof(data[0]) entries, and you need to check if the value returned by fread is the same as the number of elements you asked to read (1 in this case), otherwise a read error has occurred.

But there could also be a problem with the binary file itself, depending on how it has been generated. It would be helpful to see that code.