void Huffmancoding(Huffmantree &HT,Huffmancode &HC,int n)
{
    int s1, s2,f,c;
    Huffmantree p;
    int m,i,start;
    char *cd;
    if (n<=1)
        printf("ERROR");
    m=2*n-1;
    HT=(Huffmantree)malloc((m+1)*sizeof(Htnode));
    for (p=HT,i=1;i<=n;++i,++p)
    {
        fflush(stdin);
        printf ("请按顺序输入字符信息及对应权重：\n");
        scanf ("%c",&(*(HT+i)).letter);
        scanf ("%d",&(*(HT+i)).weight);
        (*(HT+i)).parent=0;
        (*(HT+i)).lchild=0;
        (*(HT+i)).rchild=0;
    }
    for (;i<=m;++i,++p)
    {
        (*(HT+i)).weight=0;
        (*(HT+i)).parent=0;
        (*(HT+i)).lchild=0;
        (*(HT+i)).rchild=0;
    }
    for (i=n+1;i<=m;++i)
    {
        Select(HT,i-1,s1,s2);
        HT[s1].parent=i;
        HT[s2].parent=i;
        HT[i].lchild=s1;
        HT[i].rchild=s2;
        HT[i].weight=HT[s1].weight+HT[s2].weight;
    }
    HC=(Huffmancode)malloc((n+1)*sizeof(char *));
    cd=(char*)malloc(n*sizeof(char));
    cd[n-1]='\0';
    for(i=1;i<=n;++i)
    {
        start=n-1;
        for (c=i,f=HT[c].parent;f!=0;c=f,f=HT[f].parent)
        {
            if(HT[f].lchild==c)
                cd[--start]='0';
            else
                cd[--start]='1';
            HC[i]=(char*)malloc((n-start)*sizeof(char));
        }
        strcpy(HC[i],cd);
    }   
}

调试了，但是程序中途会中断，推测是这个函数出了问题

经调试，是这个循环出了错，不懂在哪里
for (c=i,f=HT[c].parent;f!=0;c=f,f=HT[f].parent)
         {
             if(HT[f].lchild==c)
                 cd[--start]='0';
             else
                 cd[--start]='1';
             HC[i]=(char*)malloc((n-start)*sizeof(char));
         }