JNA and ZBar(library for bar code reader)

Question

I'm creating Java Interface with JNA for ZBar(library for bar code reader).

In JNA, structures in C are needed to declare. For example::

// In C
typedef struct {
    char* id;
    char* name;
    int age;
    char* sectionId
} EMPLOYEE;

to

// In Java with JNA
public static class Employee extends Structure {  // com.sun.jna.Structure
    String id;
    String name;
    int age;
    String sectionId;
}

But in ZBar, structures have no members. For example::

// zbar-0.10/include/zbar.h
// line:1009-1011
struct zbar_image_scanner_s;
/** opaque image scanner object. */
typedef struct zbar_image_scanner_s zbar_image_scanner_t;

That doesn't declare size or members of the structures.

How can I write interfaces for these structures in JNA?

Answer 1

the struct zbar_image_scanner_s is declared in img_scanner.c as:

/* image scanner state */ struct zbar_image_scanner_s { zbar_scanner_t scn; / associated linear intensity scanner */ zbar_decoder_t dcode; / associated symbol decoder */

ifdef ENABLE_QRCODE

qr_reader *qr;              /* QR Code 2D reader */

endif

const void *userdata;       /* application data */
/* user result callback */
zbar_image_data_handler_t *handler;

unsigned long time;         /* scan start time */
zbar_image_t *img;          /* currently scanning image *root* */
int dx, dy, du, umin, v;    /* current scan direction */
zbar_symbol_set_t *syms;    /* previous decode results */
/* recycled symbols in 4^n size buckets */
recycle_bucket_t recycle[RECYCLE_BUCKETS];

int enable_cache;           /* current result cache state */
zbar_symbol_t *cache;       /* inter-image result cache entries */

/* configuration settings */
unsigned config;            /* config flags */
int configs[NUM_SCN_CFGS];  /* int valued configurations */

ifndef NO_STATS

int stat_syms_new;
int stat_iscn_syms_inuse, stat_iscn_syms_recycle;
int stat_img_syms_inuse, stat_img_syms_recycle;
int stat_sym_new;
int stat_sym_recycle[RECYCLE_BUCKETS];

endif

};

not knowing what your setup (ie: ENABLE_QRCODE, NO_STATS, etc) for compilation is; I will leave the c to jna structure conversion to you, but the mapping rules as desccribe in https://jna.dev.java.net/javadoc/overview-summary.html should apply to it.