Quick file to read the floating point magnitude column from a strangely formatted fits file

Makefile

all: read_fits

read_fits: read_fits.c
	gcc $< -o $@ -lcfitsio -Wall -Wextra

read_fits.c

#include <stdio.h>
#include <fitsio.h>
#include <assert.h>

void fits_error(int status) {
    if (status) {
        fits_report_error(stderr, status);
        exit(status);
    }
}


int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <fitsfile>\n", argv[0]);
        return 1;
    }

    const char *infile = argv[1];
    int status = 0;
    fitsfile *fptr;

    fits_open_file(&fptr, infile, READONLY, &status);
    fits_error(status);

    int hdutype = 0;
    fits_movabs_hdu(fptr, 2, &hdutype, &status);
    fits_error(status);
    
    assert(hdutype == ASCII_TBL);

    int colnum = 0;
    fits_get_colnum(fptr, CASEINSEN, "Jmag", &colnum, &status);
    fits_error(status);

    printf("Found Jmag column at index %d\n", colnum);

    long nrows = 0;
    fits_get_num_rows(fptr, &nrows, &status);
    fits_error(status);

    printf("%ld rows\n", nrows);

    int typecode = 0;
    long repeat = 0;
    long width = 0;
    fits_get_coltype(fptr, colnum, &typecode, &repeat, &width, &status);
    fits_error(status);
    printf("Data type %d, repeat %ld, width %ld\n", typecode, repeat, width);

    float *data = malloc(nrows * sizeof(float));
    fits_read_col(fptr, typecode, colnum, 1, 1, nrows, 0, data, 0, &status);
    fits_error(status);

    /* Print the first 5 elements */
    int i = 0;
    for (i = 0; i < 5; i++) {
        printf("Element %d, value %f\n", i, data[i]);
    }

    free(data);
    fits_close_file(fptr, &status);
    fits_error(status);

    return 0;
}