问题描述：针对某个单位电话号码簿，设计一个哈希表，并完成相应的建表和查表程序。 基本要求：设每个记录有下列数据项：电话号码、用户名、住址。从键盘输入各记录，以用户名为关键字建立哈希表，哈希函数用除留取余数法构造，采用线性探测法解决冲突。可以插入、查找、删除并显示给定用户名的记录，并计算查找长度, 哈希表保存到文件中。 测试数据：取某个单位电话号码簿中的30 个记录。用C语言实现

以下是基于题目要求设计的哈希表的C语言实现：

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

#define MAX_RECORDS 30
#define TABLE_SIZE 50

struct record {
    char phone[12];
    char name[20];
    char address[50];
};

struct hash_table {
    struct record* table[TABLE_SIZE];
    int count;
};

unsigned int hash(char* str) {
    unsigned int hash = 0;
    int c;
    while ((c = *str++)) {
        hash = hash * 33 + c;
    }
    return hash % TABLE_SIZE;
}

void insert(struct hash_table* ht, struct record* r) {
    if (ht->count >= TABLE_SIZE) {
        printf("Error: Hash table is full\n");
        return;
    }

    int index = hash(r->name);
    while (ht->table[index] != NULL) {
        index = (index + 1) % TABLE_SIZE;
    }

    ht->table[index] = r;
    ht->count++;
}

struct record* search(struct hash_table* ht, char* name, int* length) {
    int index = hash(name);
    int i = 0;
    while (ht->table[index] != NULL && strcmp(ht->table[index]->name, name) != 0) {
        index = (index + 1) % TABLE_SIZE;
        i++;
    }
    *length = i;
    return ht->table[index];
}

void delete(struct hash_table* ht, char* name) {
    int index = hash(name);
    while (ht->table[index] != NULL) {
        if (strcmp(ht->table[index]->name, name) == 0) {
            ht->table[index] = NULL;
            ht->count--;
            return;
        }
        index = (index + 1) % TABLE_SIZE;
    }
}

void display(struct hash_table* ht) {
    for (int i = 0; i < TABLE_SIZE; i++) {
        if (ht->table[i] != NULL) {
            printf("%s %s %s\n", ht->table[i]->phone, ht->table[i]->name, ht->table[i]->address);
        }
    }
}

void save_table(struct hash_table* ht) {
    FILE* file = fopen("hash_table.dat", "wb");
    fwrite(ht->table, sizeof(struct record*), TABLE_SIZE, file);
    fclose(file);
}

void load_table(struct hash_table* ht) {
    FILE* file = fopen("hash_table.dat", "rb");
    fread(ht->table, sizeof(struct record*), TABLE_SIZE, file);
    fclose(file);
}

int main() {
    struct hash_table ht = { { 0 }, 0 };

    // Insert records
    for (int i = 0; i < MAX_RECORDS; i++) {
        struct record* r = malloc(sizeof(struct record));
        printf("Enter phone number, name, and address: ");
        scanf("%s %s %[^\n]", r->phone, r->name, r->address);
        insert(&ht, r);
    }

    // Save hash table to file
    save_table(&ht);

    // Load hash table from file
    load_table(&ht);

    // Search for record
    char name[20];
    printf("Enter name to search: ");
    scanf("%s", name);
    int length;
    struct record* r = search(&ht, name, &length);
    if (r != NULL) {
        printf("%s %s %s\n", r->phone, r->name, r->address);
        printf("Search length: %d\n", length);
    } else {
        printf("Record not found\n");
    }

    // Delete record
    printf("Enter name to delete: ");
    scanf("%s", name);
    delete(&ht, name);

    // Display hash table
    display(&ht);

    return 0;
}

该程序使用了除留取余数法作为哈希函数，并采用线性探测法解决冲突。通过 `insert` 函数将记录插入哈希表中，通过 `search` 函数查找指定用户名的记录并计算查找长度，通过 `delete` 函数删除指定用户名的记录，通过 `display` 函数显示哈希表中所有记录。此外，通过 `save_table` 函数将哈希表保存到文件中，通过 `load_table` 函数从文件中加载哈希表。