what is the mistake in this program? [closed]

问题

This is my code for finding the convolution of two signals but my output is becoming zero everytime can anyone explain the mistake in my code? I tried compling it but I'm unable to findout what is the problem my whole code is correct thanks in advance

#include<stdio.h>
#include<stdlib.h>
#define array_len(x) (sizeof(x)/sizeof(double))
void convolution(double *signal, int nt, double *wind, int r, double *rm)
{
    int i,j;
    printf("%u\n", sizeof(wind));
    int l = (nt+r-1);
    for(i=r;i<=l;i++)
    {
        wind[i]=0;
    }
        for(i=nt;i<=l;i++)
        {
            signal[i]=0;
        }
        printf("signal\n");
        for(i=0; i<=l; i++)
        {
            printf("%lf\n",signal[i]);
        }
        for(i=0;i<=l;i++)
        {
            rm[i]=0;
            for(j=0;j<=i;j++)
            {
                rm[i] = (rm[i]+(signal[j]*wind[i-j]) );
            }   
        }
}



void main()
{
    double a[] = {1,2,3,4};
    int i;
    int la = array_len(a);
    printf("\nc1\t%ld",la);
    double b[] = {1,1,1,1} ;
    int lb = array_len(b);
    printf("\nc2\t%ld\n",lb);
    double r[la+lb-1];
    int lr = array_len(r);
    printf("\nc3\t%ld\n",lr);

    printf("entering convolution\n");
    convolution(a,la,b,lb,r);

    for(i=0;i<(lr);i++)
    {
        printf("rm[%d]=%lf\n",i,r[i]);
    }
}

回答1:

You try this!

void convolution(double *signal, int nt, double *wind, int r, double *rm)
{
    int i,j;
    printf("%u\n", sizeof(wind));  // Why you do this? this just returns the size of the pointer only
    int l = (nt+r-1);
    double one[l];
    double two[l];
    for(i=0;i<l;i++)
    {
        if (i < nt)
            one[i] = signal[i];
        else
            one[i] = 0;
        if (i < r)
            two[i] = wind[i];
        else
            two[i] = 0;
    }
    printf("signal\n");
    for(i=0; i<l; i++)
        printf("%lf\n",one[i]);
    for(i=0;i<l;i++)
    {
        rm[i]=0;
        for(j=0;j<=i;j++)
        {
            rm[i] = (rm[i]+(one[j]*two[i-j]) );
        }   
    }
}

回答2:

May be not a answer to why you see 0 as answer but,

for(i=r;i<=l;i++)
{
    wind[i]=0;
}

for(i=nt;i<=l;i++)
{
    signal[i]=0;
}

length variable 'l' is (nb+r-1) i.e. 7, while array passed to convolution function, ´b´ and 'a' has only 4 elements and memory is assigned only to accommodate only 4 elements. So with your code you are crossing array boundary for wind and signal. I wonder why is it not crashing.

来源：https://stackoverflow.com/questions/16770078/what-is-the-mistake-in-this-program

标签

convolution