haader/exif.h

#include <stdint.h>
#include <iostream>

// unsigned rational number: p/q
struct urational_t {
    urational_t();
    urational_t(uint32_t p, uint32_t q);

    uint32_t p; // numerator
    uint32_t q; // denominator
};

// signed rational number: p/q
struct srational_t {
    srational_t();
    srational_t(int32_t p, int32_t q);

    int32_t p; // numerator
    int32_t q; // denominator
};

struct ExifTags {
    ExifTags();

    static bool read_from_jpeg(std::istream &stream, ExifTags &output);

    // Returns true => output reference is set to exposure time or shutter speed in seconds.
    // Returns false => do not set output because there is no valid value.
    bool get_exposure_time(double &output);

    bool ifd0_parsed_ok;
    bool exififd_parsed_ok;
    uint16_t exififd_offset;
    urational_t exposure_time;
    srational_t shutter_speed_value;
};