Sort arrays with pointers using quicksort

问题

I'm trying to sort the values in the array "tab" using quicksort, but it isn't working. the main function just set names and salaries for each tab[n]

typedef struct employee Employee;

struct employee{
  char name[81];
  float salary;
};

Employee *tab[10];

void sort(Employee **tab, int begin, int end){
  int p = tab[(begin + end) / 2] , i = end, j = begin;  
  /*p is the pivot*/
  do{
    while(tab[i]->salary < p && i < end) i++; 
    while(tab[j]->salary > p && j > begin) j--; 

    if(i <= j){
      int tmp = tab[i]->salary;
      tab[i]->salary = tab[j]->salary;
      tab[j]->salary = tmp;
      i++; j--;
    }
  }while(i <= j);

  if(begin < j) sort(tab, begin, j);
  if(end > i) sort(tab, i, end);
}

回答1:

Changes noted in comments. This is a descending order sort (as asked in a follow up question).

#include <stdio.h>

typedef struct employee{
    char name[81];
    float salary;
}Employee;

void sort(Employee **tab, int begin, int end){
    float p = tab[(begin + end) / 2]->salary; /* float needed for compare == */
    int i = begin, j = end;
    Employee *tmp;                          /* microsoft is c89 */

    while(i <= j){                      /* using while */
        while(tab[i]->salary > p) i++;  /* >, <= pivot stops scan */
        while(tab[j]->salary < p) j--;  /* <, >= pivot stops scan */
        if(i > j)                       /* using break */
            break;
        tmp = tab[i];
        tab[i] = tab[j];
        tab[j] = tmp;
        i++; j--;
    }

    if(begin < j) sort(tab, begin, j);
    if(end > i) sort(tab, i, end);
}

int main(int argc, char**argv)
{
    Employee tab[] = {{"john", 525.}, {"jack", 520.},
                      {"mary", 537.}, {"jane", 523.},
                      {"joan", 548.}, {"sam",  524.},
                      {"lisa", 527.}, {"ann",  541.},
                      {"tom",  521.}, {"ted",  531.}};
    Employee *ptr[sizeof(tab)/sizeof(tab[0])];
    int i;
    /* create array of pointers */
    for(i = 0; i < (sizeof(tab)/sizeof(tab[0])); i++)
        ptr[i] = &tab[i];
    sort(ptr, 0, sizeof(ptr)/sizeof(ptr[0])-1);
    for(i = 0; i < (sizeof(ptr)/sizeof(ptr[0])); i++)
        printf("%5s %6.2f\n", ptr[i]->name, ptr[i]->salary);
    return 0;
}

来源：https://stackoverflow.com/questions/57750049/sort-arrays-with-pointers-using-quicksort

标签

pointers

quicksort