c - 将双精度数组转换为无符号短整型

Question

  Prob = *((unsigned short*)(Prob));
  Prob = (unsigned short)(Prob);

这对我不起作用。如何正确转换？

Answer 1

您面临的最大问题是那些超过 USHRT_MAX 的双精度值。其次，您需要解决舍入问题。解决这两个问题并在.5处设置舍入的简单方法可能如下所示，其中函数array_dbl2short返回成功转换为unsigned short的双精度值的数量：

size_t array_dbl2short (unsigned short *usa, double *da, size_t n)
{
    if (!usa || !da || !n) return 0;
    register size_t i, ncnvt = 0;
    for (i = 0; i < n; i++) {
        if (da[i] < 0 || (unsigned long long)(da[i] + 0.5) > USHRT_MAX)
            fprintf (stderr, "error: %lf outside range for conversion.n",
                    da[i]);
        else
            usa[ncnvt++] = (unsigned short)(da[i] + 0.5);
    }
    return ncnvt;
}

其使用的一个简短示例是：

#include <stdio.h>
#include <limits.h>
size_t array_dbl2short (unsigned short *usa, double *da, size_t n);
int main (void) {
    double arr[] = { 1.49, 1.5, 65535.49, 65535.5, -1.9, 25671.8 };
    size_t i, n, nelem = sizeof arr/sizeof *arr;
    unsigned short usarr[nelem];
    if ((n = array_dbl2short (usarr, arr, nelem))) {
        printf ("n unsigned short array:nn");
        for (i = 0; i < n; i++)
            printf ("  usarr[%zu] : %hun", i, usarr[i]);
    }
    return 0;
}
size_t array_dbl2short (unsigned short *usa, double *da, size_t n)
{
    if (!usa || !da || !n) return 0;
    register size_t i, ncnvt = 0;
    for (i = 0; i < n; i++) {
        if (da[i] < 0 || (unsigned long long)(da[i] + 0.5) > USHRT_MAX)
            fprintf (stderr, "error: %lf outside range for conversion.n",
                    da[i]);
        else
            usa[ncnvt++] = (unsigned short)(da[i] + 0.5);
    }
    return ncnvt;
}

（注意：double值的实部必须能够表示为转换验证正常运行的unsigned long long）

示例使用/输出

$ ./bin/dbl2ushort
error: 65535.500000 outside range for conversion.
error: -1.900000 outside range for conversion.
 unsigned short array:
  usarr[0] : 1
  usarr[1] : 2
  usarr[2] : 65535
  usarr[3] : 25672

此解决方案无法解决所有可能的舍入和转换问题。您也可以在math.h中使用该功能（例如 modf、round等）来预制实部和舍入。如果您有其他问题，请告诉我。

Answer 2

您需要显式转换每个值：

unsigned short * doubleToUShort(double * Prob_double, size_t N) {
  unsigned short * Prob = malloc(sizeof(unsigned short) * N);
  size_t i = 0;
  for (i = 0; i < N; i++) {
     Prob[i] = Prob_double[i];
  }
  return Prob;
}

这将趋向于零。如果要舍入到最接近的值，可以使用#include <math.h>并将该循环更改为

for (i = 0; i < N; i++) {
  Prob[i] = round(Prob_double[i]);
}