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。用C语言实现

以下是基于题目要求的C语言实现：

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

#define MAX_LEN 20 // 字符串最大长度
#define TABLE_SIZE 13 // 哈希表大小

typedef struct Record {
    char phone[MAX_LEN];
    char name[MAX_LEN];
    char address[MAX_LEN];
} Record;

int hash_func(char *str); // 哈希函数
void insert_record(Record *table, Record r); // 插入记录
int search_record(Record *table, char *name, int *length); // 查找记录
void delete_record(Record *table, char *name); // 删除记录
void display_table(Record *table); // 显示哈希表中的记录
void save_table(Record *table); // 保存哈希表到文件中
void load_table(Record *table); // 从文件中读取哈希表

int main() {
    Record table[TABLE_SIZE] = {0}; // 初始化哈希表
    load_table(table); // 从文件中读取哈希表

    while (1) {
        printf("1. Insert record\n");
        printf("2. Search record\n");
        printf("3. Delete record\n");
        printf("4. Display table\n");
        printf("5. Save table to file\n");
        printf("6. Exit\n");
        printf("Enter your choice: ");

        int choice;
        scanf("%d", &choice);

        switch (choice) {
            case 1: {
                Record r;
                printf("Enter phone number: ");
                scanf("%s", r.phone);
                printf("Enter name: ");
                scanf("%s", r.name);
                printf("Enter address: ");
                scanf("%s", r.address);
                insert_record(table, r);
                break;
            }
            case 2: {
                char name[MAX_LEN];
                printf("Enter name to search: ");
                scanf("%s", name);
                int length;
                int index = search_record(table, name, &length);
                if (index != -1) {
                    printf("Record found at index %d, search length = %d\n", index, length);
                    printf("Phone number: %s\n", table[index].phone);
                    printf("Name: %s\n", table[index].name);
                    printf("Address: %s\n", table[index].address);
                } else {
                    printf("Record not found\n");
                }
                break;
            }
            case 3: {
                char name[MAX_LEN];
                printf("Enter name to delete: ");
                scanf("%s", name);
                delete_record(table, name);
                break;
            }
            case 4: {
                display_table(table);
                break;
            }
            case 5: {
                save_table(table);
                break;
            }
            case 6: {
                save_table(table); // 退出前保存哈希表到文件中
                exit(0);
            }
            default: {
                printf("Invalid choice\n");
                break;
            }
        }
    }

    return 0;
}

int hash_func(char *str) {
    int hash_val = 0;
    for (int i = 0; i < strlen(str); i++) {
        hash_val += str[i];
    }
    return hash_val % TABLE_SIZE;
}

void insert_record(Record *table, Record r) {
    int index = hash_func(r.name);
    int count = 0;
    while (table[index].name[0] != '\0') { // 线性探测法解决冲突
        index = (index + 1) % TABLE_SIZE;
        count++;
        if (count == TABLE_SIZE) { // 哈希表已满
            printf("Hash table full, cannot insert record\n");
            return;
        }
    }
    table[index] = r;
    printf("Record inserted at index %d\n", index);
}

int search_record(Record *table, char *name, int *length) {
    int index = hash_func(name);
    int count = 0;
    while (table[index].name[0] != '\0') { // 线性探测法解决冲突
        if (strcmp(table[index].name, name) == 0) {
            *length = count + 1;
            return index;
        }
        index = (index + 1) % TABLE_SIZE;
        count++;
        if (count == TABLE_SIZE) { // 已遍历整个哈希表，未找到记录
            break;
        }
    }
    *length = count + 1;
    return -1;
}

void delete_record(Record *table, char *name) {
    int index = search_record(table, name, NULL);
    if (index != -1) {
        table[index].name[0] = '\0'; // 将该位置的记录删除
        printf("Record deleted at index %d\n", index);
    } else {
        printf("Record not found\n");
    }
}

void display_table(Record *table) {
    printf("Index\tPhone number\tName\tAddress\n");
    for (int i = 0; i < TABLE_SIZE; i++) {
        printf("%d\t%s\t%s\t%s\n", i, table[i].phone, table[i].name, table[i].address);
    }
}

void save_table(Record *table) {
    FILE *fp = fopen("hash_table.txt", "w");
    if (fp == NULL) {
        printf("Error opening file\n");
        return;
    }
    for (int i = 0; i < TABLE_SIZE; i++) {
        fprintf(fp, "%s,%s,%s\n", table[i].phone, table[i].name, table[i].address);
    }
    fclose(fp);
    printf("Hash table saved to file\n");
}

void load_table(Record *table) {
    FILE *fp = fopen("hash_table.txt", "r");
    if (fp == NULL) {
        printf("Cannot find file, creating new hash table\n");
        return;
    }
    char line[MAX_LEN * 3 + 2];
    while (fgets(line, MAX_LEN * 3 + 2, fp) != NULL) {
        Record r;
        sscanf(line, "%[^,],%[^,],%[^\n]", r.phone, r.name, r.address);
        insert_record(table, r);
    }
    fclose(fp);
    printf("Hash table loaded from file\n");
}

注意，这个实现可能并不是最优的，例如我们可以将哈希表保存到文件中时使用更高效的二进制格式。此外，这个实现还存在一些问题，例如当哈希表已满时无法插入新记录，而且没有实现动态扩容。但是这个实现可以作为哈希表基础知识的一个参考。