c - 将数据写入动态数组时出现段错误

Question

我的任务是编写一个文件，显示用户输入的未知数量的记录。每条记录都有以下字段:名字、姓氏、地址、城市、州、邮政编码和电话号码。

我假设最好的方法是用上面的字段定义一个结构 Record，然后声明一个 Record 数组，其中包含与用户输入的记录一样多的记录。为了实现这一点，我将使用一个循环来获取每条记录的每个字段的输入，然后如果用户想继续动态地在 Record 数组中分配一个额外的空间并继续直到用户输入 no。我在以下行遇到访问冲突写入位置错误:

scanf("%s", records[i]->fname);

我的代码有什么问题？

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
struct Record;

struct Record
    {
        char fname[51];
        char lname[51];
        char address[51];
        char city[51];
        char state[51];
        int zipcode;
        int phoneNumber;
    };

int main()
{
    FILE *fileWriter;
    const char filename[] = "data.txt";
    char answer = 'y';
    int size = 1;
    int i = 0;
    struct Record **records;
    records = malloc(sizeof(*records)*(size));

    while(answer == 'y' || answer == 'Y')
    {
        printf("First Name: \n");
        scanf("%s", records[i]->fname);

        printf("Last Name: \n");
        scanf("%s", records[i]->lname);

        printf("Address: \n");
        scanf("%s", records[i]->address);

        printf("City: \n");
        scanf("%s", records[i]->city);

        printf("State: \n");
        scanf("%s", records[i]->state);

        printf("Zipcode: \n");
        scanf("%d", records[i]->zipcode);

        printf("Phone Number: \n");
        scanf("%d", records[i]->phoneNumber);
        //stores all record info

        printf("Are there anymore records? [y/n] ");
        answer = getchar();
        if(answer == 'y' || answer == 'Y')
        {
            size++;
            records[i++];
            printf("\n");
        }
        records = realloc(records,sizeof(*records)*(size));
    }

    //open file
    fileWriter = fopen(filename,"wb");

    if(fileWriter != NULL)
    {
        if(fwrite(records,sizeof(*records),size,fileWriter) != 1)
        {
            fprintf(stderr, "Failed to write to %s\n", filename);
            exit(1);
        }
        fclose(fileWriter);
    }
    else
    {
        printf("Error opening file.");
    }
}

编辑版本

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

struct Record
    {
        char fname[51];
        char lname[51];
        char address[51];
        char city[51];
        char state[51];
        int zipcode;
        int phoneNumber;
    };




int main()
{
    FILE *fileWriter;
    const char filename[] = "data.txt";
    char answer = 'y';
    int size = 1;
    int i = 0;
    struct Record *records = NULL;
    struct Record *records_temp;




    while(answer == 'y' || answer == 'Y')
    {
        struct Record *records_temp = realloc(records,(size)*sizeof(*records));

        if(records_temp == NULL)  
        {
            free(records); 

        }
        records = records_temp;
        printf("First Name: \n");
        scanf("%s", records[i].fname);
        printf("Last Name: \n");
        scanf("%s", records[i].lname);

        printf("Address: \n");
        scanf(" %[^\n]", records[i].address);

        printf("City: \n");
        scanf("%s", records[i].city);

        printf("State: \n");
        scanf("%s", records[i].state);

        printf("Zipcode: \n");
        scanf("%d", &records[i].zipcode);

        printf("Phone Number: \n");
        scanf("%d", &records[i].phoneNumber);
        //stores all record info

        printf("Are there anymore records? [y/n] ");
        answer = getchar();
        if(answer == 'y' || answer == 'Y')
        {
            size++;
            records[i++];
            printf("\n");
        }

        //open file

    fileWriter = fopen(filename,"wb");

    if(fileWriter != NULL)
    {
        if(fwrite(records,sizeof(*records),size,fileWriter) != 1)
        {
            fprintf(stderr, "Failed to write to %s\n", filename);
            exit(1);
        }
        fclose(fileWriter);
    }
    else
    {
        printf("Error opening file.");
    }
}
}

Answer 1

嗯，你会遇到段错误，因为你还没有为你的记录中的第一个实体分配内存。

所以要解决这个问题你需要

records[size-1] = malloc(sizeof(Records));

换句话说:您有 records，它是指向 Records 的指针。当你做的时候

records = malloc(sizeof(*records)*(size));

您实际上要求 size 指向 Records 的指针。但这还不够，您需要分配另一 block 内存来存储实际的 Records 因此我们必须

records[size - 1] = malloc(sizeof(Records));

注意:如果 size > 1 那么你应该这样做:

int i = 0;
for(;i < size; i++) {
    records[i] = malloc(sizeof(Records));
}

除此之外，您为什么选择 Records **，如 Arjun已经解释过了，你应该使用Records * 并修复realloc 部分-ing 新内存，因为如果realloc 失败，它返回NULL 并且在最坏的情况下您最终会出现内存泄漏或另一个段错误，无论哪种方式 - 这对您的程序都不利。

请参阅Arjun's post