JNA : Exception_Access_Violation

Question

我使用JNA在libpotrace.dll中调用这个函数，这个函数是：

potrace_state_t *potrace_trace(const potrace_param_t *param,
const potrace_bitmap_t *bm);

库中的参数为：

typedef unsigned long potrace_word;

struct potrace_bitmap_s {
  int w, h;              /* width and height, in pixels */
  int dy;                /* words per scanline (not bytes) */
  potrace_word *map;     /* raw data, dy*h words */
};
typedef struct potrace_bitmap_s potrace_bitmap_t;

struct potrace_param_s {
  int turdsize;        /* area of largest path to be ignored */
  int turnpolicy;      /* resolves ambiguous turns in path decomposition */
  double alphamax;     /* corner threshold */
  int opticurve;       /* use curve optimization? */
  double opttolerance; /* curve optimization tolerance */
  potrace_progress_t progress; /* progress callback function */
};
typedef struct potrace_param_s potrace_param_t;

在我的java代码中，我有：

public class Potrace_bitmap_t extends Structure{
    public int w=36;
    public int h=2; /* width and height, in pixels */
    public int dy=2; /* words per scanline (not bytes) */   
    public long [] map =new long[dy*h];
}

public class potrace_param_t  extends Structure{    
    //public static class ByValue extends Nat implements Structure.ByValue { }

    public int turdsize=0;
    public int turnpolicy=0;
    public double alphamax=0;
    public int opticurve=0;
    public double opttolerance=0;   

}

potrace_param_t na=lib.potrace_param_default();/*This function returns a fresh set of tracing parameters, initialized to defaults.
Potrace_bitmap_t bm=new Potrace_bitmap_t();
bm.map[0]=1113215L;
bm.map[1]=4026531840L;
bm.map[2]=3276415L;
bm.map[3]=4026531840L;
Potrace_state_t pt=lib.potrace_trace(na, bm);

当我执行potrace_trace()时，出现以下错误：

An unexpected error has been detected by Java Runtime Environment:

 EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x6504fbee, pid=2728, tid=2436

 Java VM: Java HotSpot(TM) Client VM (1.6.0_03-b05 mixed mode, sharing)
 Problematic frame:
 C  [libpotrace.dll+0xfbee]

 An error report file with more information is saved as hs_err_pid2728.log

 If you would like to submit a bug report, please visit:
  http://java.sun.com/webapps/bugreport/crash.jsp

我不明白为什么。谢谢。

Answer 1

Potrace_bitmap_t的第四个字段应该是一个指针，而不是64位值的数组。您遗漏了potrace_param_t的最后一个字段。

Answer 2

但是在图书馆的文档里，我发现了这个

w = 36;
h = 12;
dy = 2;
map[22] = 0xfff0fc02; map[23] = 0x00000000;
map[20] = 0x7ff1fe02; map[21] = 0x00000000;
map[18] = 0x3ff3ff07; map[19] = 0x00000000;
map[16] = 0x1ff7ff87; map[17] = 0x00000000;
map[14] = 0x0ff7cf8f; map[15] = 0x80000000;
map[12] = 0x07f7878f; map[13] = 0x80000000;
map[10] = 0x03f7879f; map[11] = 0xc0000000;
map[8] = 0x01f7cf9f; map[9] = 0xc0000000;
map[6] = 0x00f7ffbf; map[7] = 0xe0000000;
map[4] = 0x0073ff3f; map[5] = 0xe0000000;
map[2] = 0x0031fe7f; map[3] = 0xf0000000;
map[0] = 0x0010fc7f; map[1] = 0xf0000000;