Read binary file to integer range of -32767 to 32767

Question

I need to make a program to read a binary file into the range of -32767 to 32767. So far, the script below read the binary file into the range of -128 to 127.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  FILE *fp = NULL;
  signed char shint[2000] = "";
  int i = 0;
  size_t  bytes = 0;

  if ((fp = fopen("raw_data.ht3", "rb")) == NULL) {
    printf ("could not open file\n");
    return 0;
  }
  if ((bytes = fread(&shint, 1, 2000, fp)) > 0 ) {  //bytes more than 0
    for (i = 0; i < bytes; i++) {
      printf ("%d\n", shint[i]);
    }
  }
  fclose(fp);
  return 0;
}

More info about the binary file, my lecturer said the binary file should be read into 4 bytes data (I'm not sure my wording is right here). The data is very big so I stop the data reading till 2000 data. Though in the future I need to read all of them.

The final data representation

This is how I want to plot at the end of the day. I will call our matlab or scilab after getting the desired data.

Thanks!

Answer 1

Use 4 bytes representation for your input data, ie replace

signed char shint[2000] = "";

with

long int shint[2000] = "";

and

 if ((bytes = fread(&shint, 1, 2000, fp)) > 0 ) {  //bytes more than 0

with

 if ((bytes = fread(&shint, 4, 2000, fp)) > 0 ) {  //bytes more than 0

and

printf ("%d\n", shint[i]);

with

printf ("%ld\n", shint[i]);

---

Note:

By the name of your variable ( shint , ie short int ) and by the range -32768 to +32767 it seems that your instructor wanted 2 bytes for numbers, not 4 .
In that case use short int (or simply short ) in your declaration and 2 as the second parameter of fread() function.

Answer 2

I don't have your data to test on (and I didn't tested out my answer) but it should be something like this:

First of all signed char shint[2000] = ""; is holding 2000 signed chars (which are indeed signed 8 bit values have a look here - this is a very handy resource when handling data types sizes) , so you need some value to hold signed 32 bit (4 byte) values, which depends on your machine architecture, assuming it is 32 bit integer ( it is not difficult to find out ) you could hold you values in int shint[2000] = "";

next thing you need to pay attention to is the function fread here is some friendly documentation , the second parameter to this function (which is 1 in your code) should be the number of bytes represents a single value from the data you want to read from, so in your situation should be 4 (bytes). the other parameters should be OK.

edit: to make sure you are reading 4 bytes you can use indeed the answer given by MarianD and store long values.

Answer 3

As i understand you want easy access to chars and signed 16 bits ints.

#define SIZE 2000

union
{
    char shint_c[SIZE * 2];
    short shint[SIZE];
}su;

and then in your if

fread(&su, 2, SIZE, fp)

and in the loop to print shorts

printf ("%hd\n", su.shint[i]);

or 8 bits ints

printf ("%hhd\n", su.shint_c[i]);