字符串数组排序 C

Question

我一直试图让这个程序按列索引对二维字符串数组进行排序。

我这样初始化这个二维数组：

char *str[ROWS][COLS] = {{"Russia", "Boxing", "Mens", "Gold"},
                         {"America", "Cycling", "Mens", "Gold"}, 
                         {"New Zealand", "Swimming", "Womens", "Silver"},   
                         {"India", "Badminton", "Mens", "Bronze"}};

如果我想按第一列（国家名称）对这个数组进行排序，那么它看起来像这样：

char *str[ROWS][COLS] = {{"America", "Cycling", "Mens", "Gold"}, 
                         {"India", "Badminton", "Mens", "Bronze"}};
                         {"New Zealand", "Swimming", "Womens", "Silver"},   
                         {"Russia", "Boxing", "Mens", "Gold"}};

这是我到目前为止所做的，几乎是正确的，除了排序方法。我在实施时遇到了麻烦。

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

#define ROWS 4
#define COLS 4

void print_array(char *str[][COLS]);
void sort_array(char *str[][COLS], int nrows, int col);

int
main(void) {
    char *str[ROWS][COLS] = {{"Russia", "Boxing", "Mens", "Gold"},
                             {"America", "Cycling", "Mens", "Gold"}, 
                             {"New Zealand", "Swimming", "Womens", "Silver"}, 
                             {"India", "Badminton", "Mens", "Bronze"}};
    int col;

    /* array before sorting */
    printf("Before: \n");
    print_array(str);

    /*choosing column index to sort by*/
    printf("\nChoose which column index you wish to sort by: ");
    if (scanf("%d", &col) != 1) {
        printf("Invalid input\n");
        exit(EXIT_FAILURE);
    }

    sort_array(str, ROWS, col);

    /* array after sorting */
    printf("\nAfter: \n");
    print_array(str);

return 0;
}

void
print_array(char *str[][COLS]) {
    int i, j;

    for (i = 0; i < ROWS; i++) {
        for (j = 0; j < COLS; j++) {
            printf("%s  ", str[i][j]);
        }
        printf("\n");
    }
}

/*function used for sorting the array */
void
sort_array(char *str[][COLS], int nrows, int col) {
    int i, j;
    char *temp;

    for (i = 0; i < nrows; i++) {
        for (j = i; j < nrows; j++) {
            if(strcmp(str[i][col], str[j][col]) > 0) {
                temp = str[i][col];
                str[i][col] = str[j][col];
                str[j][col] = temp;
            }
        }
    }   
}

我遇到的问题是我的排序算法不是交换行，而是交换该列中的字符串。我也尝试使用insertion sort 算法，但我不确定如何使用二维字符串数组来实现它。

任何帮助将不胜感激:)

Answer 1

从 C11 开始，您可以按如下方式进行：

int compare_col(const void *a, const void *b, void *ctx) {
    int col = *(int*)ctx;
    return strcmp(((char**)a)[col], ((char**)b)[col]);
}

/*function used for sorting the array */
void sort_array(char *str[][COLS], int nrows, int col) {
    qsort_s(str, nrows, sizeof(char*)*COLS, compare_col, &col);
}

Answer 2

使用qsort，您需要一个比较器函数，将指针作为参数，指向要排序的两个元素。在这种情况下，要排序的元素是二维数组中的一整行。如果您需要改变排序列，您还需要使变量保持全局（否则您需要为每列创建不同的比较器）。

static int sort_column = 0;

static int compare_rows(const void *a, const void *b) {
    return strcmp(((const char **)a)[sort_column], ((const char **)b)[sort_column]);
}

然后您只需调用 qsort 并将您的数组和比较器函数作为参数：

qsort(str, ROWS, sizeof(*str), (compare_rows));

Answer 3

遍历行。比较两行的列，i 和 i + 1。根据需要遍历列并交换两行。重复直到没有交换为止。

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

#define ROWS 4
#define COLS 4

void print_array(char *str[][COLS]);
void sort_array(char *str[][COLS], int nrows, int ncols, int col);

int
main(void) {
    char *str[ROWS][COLS] = {{"Russia", "Boxing", "Mens", "Gold"},
                             {"America", "Cycling", "Mens", "Gold"},
                             {"New Zealand", "Swimming", "Womens", "Silver"},
                             {"India", "Badminton", "Mens", "Bronze"}};
    int col;
    int result = 0;
    int clean = 0;
    /* array before sorting */
    printf("Before: \n");
    print_array(str);

    /*choosing column index to sort by*/
    do {
        printf("\nChoose which column index you wish to sort by 0 to %d: ", COLS - 1);
        if ( ( result = scanf("%d", &col)) != 1) {
            printf("Invalid input\n");
            if ( result == EOF) {
                fprintf ( stderr, "problem getting input\n");
                exit(EXIT_FAILURE);
            }
            //clean input stream
            while ( ( clean = getchar ()) != '\n' && clean != EOF) {}
        }
    } while ( result != 1 || col < 0 || col >= COLS);

    sort_array(str, ROWS, COLS, col);

    /* array after sorting */
    printf("\nAfter: \n");
    print_array(str);
    return 0;
}

void
print_array(char *str[][COLS]) {
    int i, j;

    for (i = 0; i < ROWS; i++) {
        for (j = 0; j < COLS; j++) {
            printf("%s  ", str[i][j]);
        }
        printf("\n");
    }
}

/*function used for sorting the array */
void
sort_array(char *str[][COLS], int nrows, int ncols, int col) {
    int i = 0, j = 0, swap = 0;
    char *temp;

    do {
        swap = 0;
        for ( i = 0; i < nrows - 1; i++) {//iterate through rows
            if ( strcmp( str[i][col], str[i + 1][col]) > 0) {//compare col for row i and i+1
                for ( j = 0; j < ncols; j++) {//iterate through cols and swap rows
                    temp = str[i][j];
                    str[i][j] = str[i + 1][j];
                    str[i + 1][j] = temp;
                }
                swap = 1;
            }
        }
    } while ( swap);//loop until no swaps
}