c - 根据结构体内部的元素对结构体指针数组进行排序

Question

我在这里想做的是根据 Struct 内部的字符串对指向 Structs 的指针数组进行排序。我认为只交换数组内部的指针而不是交换整个 struct 会很容易。所有的Element都是动态分配的。我的代码是用德语编写的，因此我将只用英语编写我不懂的部分。预先感谢您，感谢您的帮助。

typedef struct Vehicle {
    char *manufacturer;
    char *serialnumber;
    int weight;
};
void SortByID(struct fahrzeug** data, int Anzahl){ 
    struct Vehicle *temp= (struct Vehicle*)malloc( sizeof(struct Vehicle) );
    int i =0 ;// I think i've written something wrong here ( strcmp)
    while ( i < Anzahl && strcmp(data[i]->serialnumber, data[i+1]->serialnumber) < 0) 
    {
         temp = data[i+1];
         data[i+1] = data[i];
         data[i]=temp ;
         i++;
    }  
    free(temp);
    temp=NULL;
}
int main(){
    int count =0 ;
    struct Vehicle **array = NULL ;
    array=(struct Vehicle**)malloc(  5 * sizeof(struct Vehicle*)  );
    for(int i=0;i<5 ;i++){
       array[i] = (struct Vehicle*)malloc( sizeof(struct Vehicle) ) ;
       count++;
    }
    SortByID (  &array, count ) ; // is this right ?
    return 0; 
}

我也尝试使用 qsort 函数对其进行排序，但没有成功

int compare(const void *a, const void *b) {
  struct Vehicle * const *one = a;
  struct Vehicle * const *two = b;

  return strcmp((*one)->serialnumber, (*two)->serialnumber);
}
void SortByID(struct Vehicle** data, int Anzahl){
   qsort( data, Anzahl, sizeof(struct Vehicle*) ,compare );
}

Answer 1

这是一个使用qsort()的工作示例。它可以按序列号和制造商排序。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct Vehicle {
    char *manufacturer;
    char *serialnumber;
    int weight;
};

int cmp_serialnumber(const void *p1, const void *p2)
{
    const struct Vehicle *v1 = *(struct Vehicle * const *)p1;
    const struct Vehicle *v2 = *(struct Vehicle * const *)p2;

    return strcmp(v1->serialnumber, v2->serialnumber);

/*
    // Alternatively You could write this function as this less readable one liner
    return strcmp((*(struct Vehicle * const *)p1)->serialnumber,
                    (*(struct Vehicle * const *)p2)->serialnumber);
*/
}

int cmp_manufacturer(const void *p1, const void *p2)
{
    const struct Vehicle *v1 = *(struct Vehicle * const *)p1;
    const struct Vehicle *v2 = *(struct Vehicle * const *)p2;

    return strcmp(v1->manufacturer, v2->manufacturer);
}

void print_vehicles(struct Vehicle **vehicles, int n) {
    for (int i=0; i<n; i++) {
        printf("%s, %s, %d\n", vehicles[i]->serialnumber,
                vehicles[i]->manufacturer, vehicles[i]->weight);
    }
}


#define N_VEHICLES  5
char *manufacturers[] = {"McLaren", "Ferrari", "Renault", "Mercedes", "Alfa Romeo"};
char *serialnumbers[] = {"SN500", "SN4", "SN8", "SN2", "SN1"};


int main(){
    struct Vehicle **vehicles = NULL;

    vehicles = (struct Vehicle**)malloc(N_VEHICLES * sizeof(struct Vehicle *));

    for(int i=0; i<N_VEHICLES; i++) {
        vehicles[i] = (struct Vehicle *)malloc(sizeof(struct Vehicle));
        vehicles[i]->manufacturer = manufacturers[i];
        vehicles[i]->serialnumber = serialnumbers[i];
        vehicles[i]->weight = 1000;
    }

    printf("Before\n");
    print_vehicles(vehicles, N_VEHICLES);
    printf("\n");

    // sort by serial number
    qsort(vehicles, N_VEHICLES, sizeof(struct Vehicle *), cmp_serialnumber);
    printf("Sorted by serial number\n");
    print_vehicles(vehicles, N_VEHICLES);
    printf("\n");

    // sort by manufacturer
    qsort(vehicles, N_VEHICLES, sizeof(struct Vehicle *), cmp_manufacturer);
    printf("Sorted by manufacturer\n");
    print_vehicles(vehicles, N_VEHICLES);

    return 0;
}