How to use function pointer

1 //This is a quicksort algorithm write by xiuxia,it's like C++ STL
  2 //But can be used in C
  3 #include <stdio.h>
  4 #include <stdlib.h>
  5 #include <string.h>
  6 //int cmp(int *a, int *b);
  7 typedef struct
  8 {
  9     int x;
 10     int y;
 11 }pointer;
 12
 13 int numcmp(char *s1,char *s2);
 14 void qsort_1(void *v[], int left,int right,int (*comp)(void *,void *))
 15 {
 16     int i,last;
 17     void swap(void *v[],int,int); //
 18     if(left>=right)
 19         return ;
 20     swap(v,left,(left+right)/2); //why swap ??
 21     last=left;
 22     for(i=left+1;i<=right;i++)
 23     {
 24         if( (*comp)( v[i], v[left] )<0 )
 25                     {
 26                         swap(v,++last,i);
 27                     }
 28     }
 29     swap(v,left,last);
 30     qsort_1(v,left,last-1,comp);
 31     qsort_1(v,last+1,right,comp);
 32 }
 33
 34 void swap(void *v[],int i,int j)
 35 {
 36     void *temp;
 37     temp=v[i];
 38     v[i]=v[j];
 39     v[j]=temp;
 40 }
 41
 42 int numcmp(char *s1,char *s2)
 43 {
 44     double v1,v2;
 45     v1=atof(s1);
 46     v2=atof(s2);
 47     if(v1<v2)
 46     v2=atof(s2);
 47     if(v1<v2)
 48         return -1;
 49     else if(v1>v2)
 50         return 1;
 51     else
 52         return 0;
 53 }
 54
 55 int cmp_2(pointer *a, pointer *b)
 56 {
 57     int aa=a->x;
 58     int bb=b->x;
 59     if(aa<bb)
 60         return -1;
 61     else if(aa>bb)
 62         return 1;
 63     else
 64         return 0;
 65 }
 66 int cmp(int *a, int *b)
 67 {
 68     int aa= (int)*a;
 69     int bb=(int)*b;
 70     if(aa<bb)
 71         return -1;
 72     else if(aa>bb)
 73         return 1;
 74     else
 75         return 0;
 76 }
 77
 78
 79 int main()
 80 {
 81     //int A[10]={5,8,23,12,0,3,5};
 82     int *A[10];
 83     pointer *B[5];
 84     int i;
 85     int n=7;
 86     for (i=0;i<10;i++)
 87         A[i]=(int *)malloc(4);
 88     *A[0]=9;
 89     *A[1]=8;
 90     *A[2]=23;
 91     *A[3]=12;
 92     for(i=0;i<4;i++)
 91     *A[3]=12;
 92     for(i=0;i<4;i++)
 93     {
 94         printf("%d\n",*A[i]);
 95     }
 96
 97     qsort_1((void **)&A,0,4-1,(int (*)(void *,void *))cmp);
 98     for(i=0;i<4;i++)
 99     {
100         printf("%d\n",*A[i]);
101     }
102
103     //about B
104
105     for (i=0;i<5;i++)
106         B[i]=(pointer *)malloc(sizeof(pointer));
107
108     B[0]->x=7;
109     B[0]->y=9;
110
111     B[1]->x=0;
112     B[1]->y=6;
113
114     B[2]->x=4;
115     B[2]->y=2;
116
117     B[3]->x=3;
118     B[3]->y=5;
119     qsort_1((void **)B,0,3,(int (*)(void *, void *))cmp_2 );
120     printf("-------------------------------------\n");
121             for(i=0;i<3;i++)
122             {
123                printf("%d %d\n",B[i]->x,B[i]->y);
124             }
125     printf("-------------------------------------\n");
126     char *lineptr[4];
127
128     lineptr[0]=(char *)malloc(sizeof(char)*10);
129     strcpy(lineptr[0],"zhang");
130     lineptr[1]=(char *)malloc(sizeof(char)*10);
131     strcpy(lineptr[1],"xiu");
132     lineptr[2]=(char *)malloc(sizeof(char)*10);
133     strcpy(lineptr[2],"xia");
134
135     lineptr[3]=(char *)malloc(sizeof(char)*10);
136     strcpy(lineptr[3],"love");
137
136     strcpy(lineptr[3],"love");
137
138     lineptr[4]=(char *)malloc(sizeof(char)*10);
139     strcpy(lineptr[4],"life");
140
141     qsort_1((void **)lineptr,0,4,(int (*)(void *, void *))strcmp);
142
143     for(i=0;i<5;i++)
144         printf("%s\n",lineptr[i]);
145     return 0;
146 }

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