函数泛型Lecture09.pdfbubble_sort.ccount_matches.ccount_matches_soln.clive_session.cprint_array.cprint_array_soln.c

memset

Bubble Sort

// This is a generic function to swap two variables of the same type.
void swap(void *a, void *b, int elem_size_bytes) {
    char temp[elem_size_bytes];
    memcpy(temp, a, elem_size_bytes);
    memcpy(a, b, elem_size_bytes);
    memcpy(b, temp, elem_size_bytes);
}
// This is a standard comparison function for integers.
int int_cmpfn(void *a, void *b) {
    return *(int *)a - *(int *)b;
}
// This is a standard comparison function for strings.
int str_cmpfn(void *a, void *b) {
    char *str1 = *(char **)a;
    char *str2 = *(char **)b;
    return strcmp(str1, str2);
}
/* This is a generic bubble sort function to sort an array of any type.
 * It accepts a comparison function as a parameter to properly compare elements. */
void bubble_sort(void *arr, int n, int elem_size_bytes, int (*cmpfn)(void *a, void *b)) {
    while (true) {
        bool swapped = false;
        for (int i = 1; i < n; i++) {
            void *p_prev_elem = (char *)arr + (i - 1) * elem_size_bytes;
            void *p_curr_elem = (char *)arr + i * elem_size_bytes;
            if (cmpfn(p_prev_elem, p_curr_elem) > 0) {
                swapped = true;
                swap(p_prev_elem, p_curr_elem, elem_size_bytes);
            }
        }
        if (!swapped) {
            return;
        }
    }
}
void test_sort() {
    int nums[] = {4, 2, 12, -5, 56, 14};
    int nums_count = sizeof(nums) / sizeof(nums[0]);
    bubble_sort(nums, nums_count, sizeof(nums[0]), int_cmpfn);
    for (int i = 0; i < nums_count; i++) {
        printf("%d  ", nums[i]);
    }
    printf("\n");
}
void test_sort_args(char *args[], int nargs) {
    bubble_sort(args, nargs, sizeof(args[0]), str_cmpfn);
    for (int i = 0; i < nargs; i++) {
        printf("%s ", args[i]);
    }
    printf("\n");
}
int main(int argc, char *argv[]) {
    if (argc == 1) {
        test_sort();
    } else {
        test_sort_args(argv + 1, argc - 1);
    }
    return 0;
}

Function Pointers

Example: Generic Printing

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

/* This struct stores information about temperature info (in Fahrenheit)
 * for a given month, including average low and high temps.
 */
typedef struct month_temp_info {
    char *month;
    int avg_high_f;
    int avg_low_f;
} month_temp_info;

/* This function prints out the provided array using
 * the provided function that prints out one element of the array.
 */
void print_array(void *arr, size_t nelems, int elem_size_bytes,
                 void(*print_fn)(void *)) {
    for (int i = 0; i < nelems; i++) {
        void *elem_ptr = (char *)arr + i * elem_size_bytes;
        printf("%d: ", i + 1);
        print_fn(elem_ptr);
        printf("\n");
    }
}

void print_int(void *arr) {
    printf("%d", *(int *)arr);
}

void print_long(void *arr) {
    printf("%ld", *(long *)arr);
}

void print_temp_info(void *arr) {
    month_temp_info info = *(month_temp_info *)arr;
    printf("In %s, the average high was %doF, and the average low was %doF",
           info.month, info.avg_high_f, info.avg_low_f);
}

int main(int argc, char *argv[]) {
    // Print an array of ints
    int i_array[] = {0, 1, 2, 3, 4, 5};
    size_t i_nelems = sizeof(i_array) / sizeof(i_array[0]);
    print_array(i_array, i_nelems, sizeof(i_array[0]), print_int);
    printf("\n");

    // Print an array of longs
    long l_array[] = {0, 10, 20, 30, 40, 50};
    size_t l_nelems = sizeof(l_array) / sizeof(l_array[0]);
    print_array(l_array, l_nelems, sizeof(l_array[0]), print_long);
    printf("\n");

    // Print an array of temp info structs
    // data from https://www.usclimatedata.com/climate/winters/california/united-states/usca1252
    month_temp_info month_temps[3];
    month_temps[0] = (month_temp_info){"January", 56, 38};
    month_temps[1] = (month_temp_info){"April", 75, 49};
    month_temps[2] = (month_temp_info){"June", 92, 59};
    size_t temp_nelems = sizeof(month_temps) / sizeof(month_temps[0]);
    print_array(month_temps, temp_nelems, sizeof(month_temps[0]), print_temp_info);

    return 0;
}

Function Pointers As Variables

Generic C Standard Library Functions

Pre-lecture Quiz 4 Q1

Common code snippets

Function pointers as variables