程序代码：

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
void  wrt(int key[], int sz);
void  mergesort(int key[], int n);
void  merge(int a[], int b[], int c[], int m, int n);


void merge(int a[],int b[],int c[], int m,int n)
{
    int i=0,j=0,k=0;
    while(i<m && j<n)
        if(a[i] < b[i])
            c[k++]=a[i++];
        else
            c[k++]=b[j++];
        while (i<m)
            c[k++]=a[i++];
        while (j<n)
            c[k++] = b[j++];
}
void mergesort(int key[],int n)
{
    int j,k,m,*w;
    for(m = 1; m < n; m *= 2)
        ;
    if (n < m)
    {
        printf("ERROR:Array size not apower of 2 - bye!\n");
        exit(1);
    }
    w = calloc(n, sizeof(int));
    assert(w != NULL);
    for (k = 1; k < n; k *=2)
    {
        for(j = 0; j < n - k; j += 2*k)
            merge(key + j, key + j + k, w + j, k, k);

        for (j = 0; j < n; ++j)
            key[j] = w[j];
    }



    free(w);
}


void wrt(int key[], int sz)
{
    int  i;
    for (i = 0; i <sz; ++i)
        printf("%4d%s",key[i],((i < sz - 1) ? "" : "\n"));
}
int main(void)
{
    int sz,key[]={ 4, 3, 6, 67,5,8,7,9};
    sz=sizeof(key) / sizeof(int);
    printf("Before mergesort:\n");
    wrt(key,sz);
    mergesort(key,sz);
    printf("After mergesort:\n");
    wrt(key,sz);
    return 0;
}