C-浮点异常（核心已转储）

Question

This function is supposed to, pixel by pixel, blur the image by turning the color of each pixel on the mean of the colors around it in a 2n+1 "radius".

(The part where it skips to the next pixel is already implemented, don't worry).

I successfully compiled this code:

void
blur_pixels(image *img, pixel *p, size_t i, size_t j)
{
  //i = current height of pixel, j = current width of pixel
  int side = 2*blurRate+1;
  int total = 0;
  int leftRight = i-blurRate;
  int upDown = j-blurRate;
  int tmpHr = 0, tmpHg = 0, tmpHb = 0;

  for(; upDown < j+blurRate; upDown++) {
    if(upDown >= 0 && upDown < img->height) {
      for(; leftRight < i+blurRate; leftRight++) {
        if(leftRight >= 0 && leftRight < img->width) {
          tmpHr += (p+leftRight)->r;
          tmpHg += (p+leftRight)->g;
          tmpHb += (p+leftRight)->b;
          total++;
        }
      }
    }
  }
  p->r=tmpHr/total;
  p->g=tmpHg/total;
  p->b=tmpHb/total;
}

But when I run the code I get the following exception:

Floating point exception

Does anyone know why?

Answer 1

Code is preforming division by 0 with p->r=tmpHr/total;

total is likely zero because compiler warnings are not turned on showing the mixed signed/unsigned math of the for() loop. Turn on all compiler warnings.

The compare upDown < j+blurRate and other code is done using unsigned math, likely not as OP expects and the inner total++; never happens. If upDown < 0 , then upDown in upDown < j+blurRate becomes a large unsigned value. Then compare is false.

size_t j  // an unsigned type
...
int upDown = j-blurRate;
...
for(; upDown < j+blurRate; upDown++) {  // not firing

One solution would be to use only int variables. A more robust solution would use unsigned math, yet more of the higher level code would be needed for a good answer.

Something like:

blur_pixels(image *img, pixel *p, size_t i, size_t j) {
  //i = current height of pixel, j = current width of pixel
  size_t side = 2u*blurRate+1;
  size_t total = 0;
  size_t leftRight = (i > blurRate) ? i-blurRate : 0;
  size_t upDown = (j > blurRate) ? j-blurRate : 0;
  int tmpHr = 0, tmpHg = 0, tmpHb = 0;

  for(; upDown < j+blurRate; upDown++) {
    if (upDown < img->height) {
      // I suspect leftRight needs to be set here each iteration
      size_t leftRight = (i > blurRate) ? i-blurRate : 0;
      for(; leftRight < i+blurRate; leftRight++) {
        if (leftRight < img->width) {
          tmpHr += (p+leftRight)->r;
          tmpHg += (p+leftRight)->g;
          tmpHb += (p+leftRight)->b;
          total++;
        }
      }
    }
  }
  if (total) {
    p->r = tmpHr/total;
    p->g = tmpHg/total;
    p->b = tmpHb/total;
  } else {
    p->r = p->g = p->b = 0;
  }
}