C语言 使用qsort的排序结构

Question

我必须使用快速排序来按年龄等于或大于65岁的人口百分比对各州进行排序。我不知道如何在函数中使用它。

我似乎不能改变比较函数。我还必须创建一个新的文件，称为输出文件。我使用选择排序对文件进行排序。

struct state {
char state_name[150];
int population_2020;
int population_2010;
double ages_under_5;
double ages_under_18;
double ages_65_or_greater;
};
void sort_states(struct state list[], int n) 
{
int i, j, p;
struct state temp;
for (i = 0; i < n; i++) {
p = i;
for (j = i + 1; j < n; j++) {
if (list[p].ages_65_or_greater < list[j].ages_65_or_greater) {
p = j;
}
}
temp = list[p];
list[p] = list[i];
list[i] = temp;
}
}
int main()
{
char input_file_open[100]; /* initializing the variables */
char output_file_name[110];
printf("Enter the file name: n");
scanf("%s", input_file_open);
FILE *input_file = fopen(input_file_open, "r"); 
FILE *output_file;
struct state list[100];
int i, n = 0;
do {
fscanf(input_file, "%[^,], %d, %d, %lf, %lf, %lfn",
list[n].state_name, &list[n].population_2020,
&list[n].population_2010, &list[n].ages_under_5,
&list[n].ages_under_18, &list[n].ages_65_or_greater);
n++;
} while (!feof(input_file));
fclose(input_file);
for (i = 0; i < n; i++) {
qsort(input_file, n, sizeof(int), sort_states);
}
return 0;
}

Answer 1

你必须为你的结构定义一个比较函数:

int state_compare_by_age_65_or_gt(const void *s1, const void *s2)
{
const struct state *ss1 = s1;
const struct state *ss2 = s2;

if (ss1->ages_65_or_greater < ss2->ages_65_or_greater)
return -1;
else if (ss1->ages_65_or_greater > ss2->ages_65_or_greater)
return 1;
else
return 0;
}

和一个打印状态的函数(用于测试目的，但您也可以将其用于非测试目的):

void state_print(const struct state *st)
{
printf("%st%dt%dt%.2lft%.2lft%.2lf",
st->state_name,
st->population_2020,
st->population_2010,
st->ages_under_5,
st->ages_under_18,
st->ages_65_or_greater
);
}

现在你可以使用它与qsort():

int main(void)
{
struct state states[] = {
{"state1", 100, 200, 2.0, 3.0, 13.0},
{"state2", 100, 200, 2.0, 4.0, 10.0},
{"state3", 100, 200, 2.0, 5.0, 12.0},
{"state4", 100, 200, 2.0, 6.0, 11.0},
{"state5", 100, 200, 2.0, 7.0, 36.0},
{"state6", 100, 200, 10.0, 8.0, 140.0},
};
qsort(states, 6, sizeof(struct state), state_compare_by_age_65_or_gt);
for (int i = 0; i < 6; i++) {
state_print(&states[i]);
puts("");
}
}

输出:

state2  100 200 2.00    4.00    10.00
state4  100 200 2.00    6.00    11.00
state3  100 200 2.00    5.00    12.00
state1  100 200 2.00    3.00    13.00
state5  100 200 2.00    7.00    36.00
state6  100 200 10.00   8.00    140.00

Answer 2

或者，您可以使用结构指针数组来进行最佳排序。

1. 输入文件(借鉴以上答案)

state1, 111, 211, 2.0, 3.0, 13.0
state2, 222, 322, 2.0, 4.0, 10.0
state3, 333, 433, 2.0, 5.0, 12.0
state4, 444, 544, 2.0, 6.0, 11.0
state5, 555, 655, 2.0, 7.0, 36.0
state6, 666, 755, 10.0, 8.0, 140.0

2. qsort使用结构指针:

#include <stdio.h>
#include <stdlib.h>
#define str(x)          # x
#define xstr(x)         str(x)
#define MAX_NAME_LEN    127
typedef struct {
char name [MAX_NAME_LEN +1];
int pop_2020;
int pop_2010;
double age_lt5;     // less than 5
double age_lt18;
double age_gte65;    // greater or equal
} state_dtls;
int qsort_cmp (const void *p, const void *q) {
state_dtls *x = *(state_dtls **) p;
state_dtls *y = *(state_dtls **) q;
return (x->age_gte65 < y->age_gte65);
}
#define RECORD_STEP_SZ 2
int main() {
char in_file[MAX_NAME_LEN + 1]; /* intializing the variables */
char out_file[MAX_NAME_LEN + 1];
printf ("Enter Input file name: ");
scanf (" %" xstr(MAX_NAME_LEN) "s", in_file);
printf ("Enter Output file name: ");
scanf (" %" xstr(MAX_NAME_LEN) "s", out_file);
FILE *ipFile = fopen (in_file, "r");
if (!ipFile) {
perror ("Error Opening Input File"); return 1;
}
int rec_step = 0;
state_dtls** SPA = malloc (sizeof (state_dtls*) * RECORD_STEP_SZ * (++rec_step)); // state-details pointers array
if (!SPA) {
perror ("Error malloc SPA"); return 3;
}
int records = 0;
for (int ri = 0; 1; ++ri) {
state_dtls* sd = malloc (sizeof (state_dtls));
if (!sd) {
perror ("Error malloc state-dtls"); return 4;
}
if ((rec_step * RECORD_STEP_SZ) == ri) { // need more space for pointers
SPA = realloc (SPA, sizeof (state_dtls*) * RECORD_STEP_SZ * (++rec_step));
if (!SPA) {
perror ("Error malloc SPA2"); return 5;
}
}
if (6 != fscanf (ipFile, "%[^,], %d, %d, %lf, %lf, %lfn",
sd->name, &sd->pop_2020, &sd->pop_2010,
&sd->age_lt5, &sd->age_lt18, &sd->age_gte65)) {
printf ("Error reading record [%d]n", ri +1);
records = ri;
free (sd);
break; // break the loop // EOF
}
SPA[ri] = sd;
}
fclose (ipFile);
qsort (SPA, records, sizeof (state_dtls*), qsort_cmp);
// write to output file
FILE *opFile = fopen (out_file, "w");
if (!opFile) {
perror ("Error Opening output File"); return 2;
}
for (int ri = 0; ri < records; ++ri) {
fprintf (opFile, "%s, %d, %d, %lf, %lf, %lfn",
SPA[ri]->name, SPA[ri]->pop_2020, SPA[ri]->pop_2010,
SPA[ri]->age_lt5, SPA[ri]->age_lt18, SPA[ri]->age_gte65);
free (SPA[ri]); // free memory resources as well
}
free (SPA);
fclose (opFile);
return 0;
}

3. age_gte65参数降序输出文件:

state6, 666, 755, 10.000000, 8.000000, 140.000000
state5, 555, 655, 2.000000, 7.000000, 36.000000
state1, 111, 211, 2.000000, 3.000000, 13.000000
state3, 333, 433, 2.000000, 5.000000, 12.000000
state4, 444, 544, 2.000000, 6.000000, 11.000000
state2, 222, 322, 2.000000, 4.000000, 10.000000