c - 在 C 中编写/分配字符串列表

Question

我正在用 C 语言创建一个字符串列表，但我在网上找不到任何可以轻松添加然后清除字符串列表的内容。这与 Perl 的“推送”功能很接近。

我想在这里分享我想出的代码:

#include <stdio.h>//printf
#include <stdlib.h>//EXIT_FAILURE, malloc, realloc
#include <string.h>//need for strcmp and strlen

void *add_name(char **restrict array, size_t *restrict size, size_t *restrict number_of_names, const char *restrict NAME) {//this function works, when freed inside main()
    for (unsigned int name = *number_of_names-1; name <= 0; name--) {
        if (strcmp(array[name], NAME) == 0) {
            return array;//if this name is already in the list, don't add it
        }
    }
    const size_t NAME_SIZE = strlen(NAME)*sizeof(char)+sizeof(char*);
    *size += NAME_SIZE;
    array = realloc(array, *size);
    if (array == NULL) {
        puts("realloc of array failed.\n");
        exit(EXIT_FAILURE);
    }
    array[*number_of_names] = malloc(NAME_SIZE);
    if (array[*number_of_names] == NULL) {
        printf("alloc of array[%zu] failed.\n", *number_of_names);
        exit(EXIT_FAILURE);
    }
    strcpy(array[*number_of_names], NAME);
    *number_of_names += 1;
    return array;
}

void *clear_names(char **restrict array, size_t *restrict size, size_t *restrict number_of_names) {//empty the list of names
    for (size_t name = 0; name < *number_of_names; name++) {
        free(array[name]); array[name] = NULL;//this is missing something
        if (array[name] != NULL) {
            printf("free of array[%zu] failed.\n", name);
        }
    }
    *number_of_names = 0;
    *size = sizeof(char);
    array = realloc(array, *size);
    if (array == NULL) {
        printf("realloc of array failed @ line %u\n",__LINE__);
        exit(EXIT_FAILURE);
    }
    return array;
}

int main (void) {
    puts("This program demonstrates how to add to and clear a list of names.");
    size_t name_list_size = sizeof(char);
    char **name_list = malloc(name_list_size);
    size_t number_of_names = 0;
    name_list = add_name(name_list, &name_list_size, &number_of_names, "James");
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Mary");
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Mary");
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Thomas");
    for (size_t name = 0; name < number_of_names; name++) {
        printf("%s\n",name_list[name]);
    }
    name_list = clear_names(name_list, &name_list_size, &number_of_names);
//
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Matthew");
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Mark");
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Luke");
    name_list = add_name(name_list, &name_list_size, &number_of_names, "John");
    for (size_t name = 0; name < number_of_names; name++) {
        printf("%s\n",name_list[name]);
    }
//
    name_list = clear_names(name_list, &name_list_size, &number_of_names);
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Titus");
    printf("size = %zu  number_of_names = %zu\n", name_list_size, number_of_names);
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Peter");
    printf("size = %zu  number_of_names = %zu\n", name_list_size, number_of_names);
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Bartholomew");
    printf("size = %zu  number_of_names = %zu\n", name_list_size, number_of_names);
    name_list = add_name(name_list, &name_list_size, &number_of_names, "Paul");
    printf("size = %zu  number_of_names = %zu\n", name_list_size, number_of_names);
    for (size_t name = 0; name < number_of_names; name++) {
        printf("%s\n",name_list[name]);
    }
    name_list = clear_names(name_list, &name_list_size, &number_of_names);
    free(name_list); name_list = NULL;
    return 0;
}

Answer 1

我提出以下建议:

• 将realloc分配给临时指针，因此如果它返回NULL，则不会破坏数组
• 使用 strdup 而不是 malloc 进行字符串存储
• 使用lsearch检查并插入字符串
• 当增加数组的大小时，通过加倍而不是线性来实现
• 将数组及其数量和容量打包在 struct 中(见下文)，并将其作为参数传递给 add 和clear 函数

您需要添加一个比较函数以传递给lsearch。如果 lsearch 添加名称，它会更新计数。分配仍然取决于您，因此在调用之前请确保容量超过计数。

如果你这样做，我想你会发现你的代码更小更简单。它还有助于添加删除和搜索功能。

使用该结构的一个优点是您可以使用较短的名称，例如:

struct name_list_t { 
       char **array; 
       size_t n, capacity; } names = { .array = NULL };

//this function works, when freed inside main()

嗯。该评论实际上没有意义，因为函数没有被释放。我明白你的意思，但你让我工作。

HTH。