C语言通讯录系统以文件的方式保存通讯录信息

可以使用文件来保存通讯录信息，这样可以实现信息的持久化存储。具体实现方法如下：

1. 定义联系人结构体

typedef struct {
    char name[20];
    char phone[12];
    char email[30];
} Contact;

2. 定义文件名和文件打开方式

#define FILENAME "contacts.txt"
#define MODE "r+b"

3. 实现添加联系人函数

void add_contact() {
    Contact c;
    FILE* fp = fopen(FILENAME, MODE);
    if (fp == NULL) {
        printf("Failed to open file\n");
        return;
    }
    printf("Enter name: ");
    scanf("%s", c.name);
    printf("Enter phone number: ");
    scanf("%s", c.phone);
    printf("Enter email: ");
    scanf("%s", c.email);
    fwrite(&c, sizeof(Contact), 1, fp);
    printf("Contact added successfully.\n");
    fclose(fp);
}

4. 实现查找联系人函数

void find_contact() {
    char name[20];
    Contact c;
    FILE* fp = fopen(FILENAME, MODE);
    if (fp == NULL) {
        printf("Failed to open file\n");
        return;
    }
    printf("Enter name to search: ");
    scanf("%s", name);
    while (fread(&c, sizeof(Contact), 1, fp) != 0) {
        if (strcmp(c.name, name) == 0) {
            printf("Name: %s\n", c.name);
            printf("Phone: %s\n", c.phone);
            printf("Email: %s\n", c.email);
            fclose(fp);
            return;
        }
    }
    printf("Contact not found.\n");
    fclose(fp);
}

5. 实现删除联系人函数

void delete_contact() {
    char name[20];
    Contact c;
    FILE* fp = fopen(FILENAME, MODE);
    if (fp == NULL) {
        printf("Failed to open file\n");
        return;
    }
    printf("Enter name to delete: ");
    scanf("%s", name);
    FILE* tmp = tmpfile();
    while (fread(&c, sizeof(Contact), 1, fp) != 0) {
        if (strcmp(c.name, name) != 0) {
            fwrite(&c, sizeof(Contact), 1, tmp);
        }
    }
    fclose(fp);
    fp = fopen(FILENAME, "wb");
    rewind(tmp);
    while (fread(&c, sizeof(Contact), 1, tmp) != 0) {
        fwrite(&c, sizeof(Contact), 1, fp);
    }
    fclose(fp);
    printf("Contact deleted successfully.\n");
}

6. 实现修改联系人函数

void update_contact() {
    char name[20];
    Contact c;
    FILE* fp = fopen(FILENAME, MODE);
    if (fp == NULL) {
        printf("Failed to open file\n");
        return;
    }
    printf("Enter name to update: ");
    scanf("%s", name);
    FILE* tmp = tmpfile();
    while (fread(&c, sizeof(Contact), 1, fp) != 0) {
        if (strcmp(c.name, name) == 0) {
            printf("Enter new name: ");
            scanf("%s", c.name);
            printf("Enter new phone number: ");
            scanf("%s", c.phone);
            printf("Enter new email: ");
            scanf("%s", c.email);
        }
        fwrite(&c, sizeof(Contact), 1, tmp);
    }
    fclose(fp);
    fp = fopen(FILENAME, "wb");
    rewind(tmp);
    while (fread(&c, sizeof(Contact), 1, tmp) != 0) {
        fwrite(&c, sizeof(Contact), 1, fp);
    }
    fclose(fp);
    printf("Contact updated successfully.\n");
}

7. 实现显示所有联系人函数

void show_all_contacts() {
    Contact c;
    FILE* fp = fopen(FILENAME, MODE);
    if (fp == NULL) {
        printf("Failed to open file\n");
        return;
    }
    while (fread(&c, sizeof(Contact), 1, fp) != 0) {
        printf("Name: %s\n", c.name);
        printf("Phone: %s\n", c.phone);
        printf("Email: %s\n", c.email);
        printf("\n");
    }
    fclose(fp);
}

注意事项：

1. 文件打开方式为 "r+b"，表示以读写方式打开二进制文件，如果文件不存在则创建。
2. 查找、删除和修改联系人时需要使用临时文件进行操作，最后再将临时文件内容复制回原文件。
3. 代码中没有对输入的数据进行校验和验证，需要自行添加。