C语言嵌套结构体与动态内存分配开发保单管理的运行异常求助

问题1：输入流程崩溃修复 #

根因 #

• getmember函数获取用户输入的保单数量polnum后，未给成员的policy指针分配动态内存，直接对野指针写入触发内存访问异常
• 循环录入保单ID时写死了member.policy->id，仅能操作第一个保单的ID字段，后续保单操作越界

修复代码（getmember函数内新增/修改部分） #

if (member.polnum > 0) { 
    // 新增：给policy数组分配对应数量的内存
    member.policy = (pol*)malloc(member.polnum * sizeof(pol));
    printf("\nEnter policy details for %s", member.name);
    for (i = 0; i < member.polnum; i++) {
        printf("\nEnter details for policy %d", i + 1);
        printf("\nEnter Policy ID: ");
        // 修改：按索引访问第i个保单的ID
        scanf(" %s", member.policy[i].id);
        // 后续原有逻辑不变

问题2：打印功能异常修复 #

根因 #

1. 无成员时打印无效内容：main函数初始化阶段错误执行了member = (mem*)realloc(member, (memNum++) * sizeof(member));，memNum初始为0，实际分配了0长度的内存却把memNum置为1，导致误认为存在1个空成员
2. 录入成员后打印异常：
   • printmember的循环条件写为赋值语句i = memNum+1，既存在越界访问，又永远从索引1开始遍历，跳过了第一个有效成员
   • 打印保单类型的printf语句多余传入了类型参数，没有对应占位符，导致前缀Policy Type:后无拼接输出
   • 打印逻辑未判断policy是否为NULL，空指针访问会触发崩溃

修复点 #

1. 删掉main函数初始化阶段多余的realloc语句，初始状态member = NULL、memNum=0即可
2. 修改printmember的遍历逻辑：

void printmember(mem* member, int memNum) {
    int i, j;
    // 修改：从索引0开始遍历，判断条件为i < memNum
    for (i = 0; i < memNum; i++) {
        printf("\n\nMember ID: %d", member[i].id);
        printf("\nMember Name: %s", member[i].name);
        // 新增：判断policy是否非空再遍历保单
        if (member[i].polnum > 0 && member[i].policy != NULL) {
            for (j = 0; j < member[i].polnum; j++) {
                printf("\nPolicy ID: %s", member[i].policy[j].id);
                // 修改：删掉多余的参数，固定打印前缀
                printf("\nPolicy Type: ");
                switch (member[i].policy[j].type) { 
                case 1:
                    printf("Car");
                    break;
                case 2:
                    printf("Health");
                    break;
                case 3:
                    printf("Travel");
                    break;
                case 4:
                    printf("Pet");
                    break;
                }
                printf("\nPremium: $%d", member[i].policy[j].premium);
            }
        }
    }
}

完整修复后代码 #

#include <malloc.h>
#include <stdio.h>

enum enumtype { Car, Health, Travel, Pet };

typedef struct policy {
        char id[4];
        enum enumtype type;
        int premium;
}pol;

typedef struct member {
    int id;
    char name[30];
    int polnum;
    pol *policy;
}mem;

mem getmember() {
    mem member;
    int i, j;

    printf("\n\nEnter member's details");
    printf("\nMember ID: ");
    scanf("%d", &member.id);
    printf("Member Name: ");
    scanf(" %s", member.name);
    printf("Requested number of policies: ");
    scanf("%d", &member.polnum);

    if (member.polnum > 0) { 
        member.policy = (pol*)malloc(member.polnum * sizeof(pol));
        printf("\nEnter policy details for %s", member.name);
        for (i = 0; i < member.polnum; i++) {
            printf("\nEnter details for policy %d", i + 1);
            printf("\nEnter Policy ID: ");
            scanf(" %s", member.policy[i].id);

            printf("\nEnter Policy Type:");
            printf("\n1 - Car");
            printf("\n2 - Health");
            printf("\n3 - Travel");
            printf("\n4 - Pet");
            printf("\n\nEnter an option: ");
            scanf("%d", &member.policy[i].type);

            while (member.policy[i].type < 1 || member.policy[i].type > 4) {
                printf("\nInvalid policy type");
                printf("\nPlease enter a number from 1 - 4: ");
                scanf("%d", &member.policy[i].type);
            }

            printf("\nEnter Premium: $");
            scanf("%d", &member.policy[i].premium);

            while (member.policy[i].premium < 0) {
                printf("Invalid premium");
                printf("\nPremium must be a positive value");
                printf("\nEnter Premium: $");
                scanf("%d", &member.policy[i].premium);
            }
        }
    }
    else
        member.policy = NULL;
    
    return member;
}

void printmember(mem* member, int memNum) {

    int i, j;

    for (i = 0; i < memNum; i++) {
        printf("\n\nMember ID: %d", member[i].id);
        printf("\nMember Name: %s", member[i].name);

        if (member[i].polnum > 0 && member[i].policy != NULL) {
            for (j = 0; j < member[i].polnum; j++) {
                printf("\nPolicy ID: %s", member[i].policy[j].id);
                printf("\nPolicy Type: ");
                switch (member[i].policy[j].type) { 
                case 1:
                    printf("Car");
                    break;
                case 2:
                    printf("Health");
                    break;
                case 3:
                    printf("Travel");
                    break;
                case 4:
                    printf("Pet");
                    break;
                }
                printf("\nPremium: $%d", member[i].policy[j].premium);
            }
        }
    }
}

int main()
{
    int choice = 0;
    int memNum = 0;
    mem* member = NULL;

    while (choice != 3) {
        
        choice = 0;
        printf("\n\t   Menu");
        printf("\n-----------------------------");
        printf("\n1 - Add new member");
        printf("\n2 - Display all members");
        printf("\n3 - Exit");
        
        printf("\n\nEnter an option: ");
        scanf("%d", &choice);
        
        switch (choice) {
        case 1:
            member = (mem*)realloc(member, (memNum + 1) * sizeof(member));
            member[memNum++] = getmember();
            break;
        case 2:
            printf("\n\nDisplaying all members");
            printmember(member, memNum);
            break;
        case 3:
            // 释放动态内存避免泄漏
            for (int i = 0; i < memNum; i++) {
                if (member[i].policy != NULL) {
                    free(member[i].policy);
                }
            }
            free(member);
            return 0;
        }
    }
}

内容的提问来源于stack exchange，提问作者WetWizard