Question

我正在编写一个程序来创建一个用于创建列表的结构，但是我遇到了双重自由或损坏错误。我知道链接列表是一个更好的实现，但我想知道我在这里做错了什么。代码在我的IDE中完美运行，但显示了在Ubuntu的终端上使用GCC运行时出现上述错误。

/* Implements an employee structure having name and company name
and can take new employees, delete last employee and display entire list of employees */

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

// defining structure employee
typedef struct emp
{
    char name[20];
    char company[20];
}emp;


int p = 0, size = 0;

void create(emp *);
void del(emp *);
void display(emp *);

int main(void)
{
    emp *buffer = malloc(sizeof(emp));
    if (buffer == NULL)
    {
        printf("Error");
        exit(1);
    }
    int n = 0;
    do
    {
        printf("The options are:\n");
        printf("1. Add employee\n");
        printf("2. Delete employee\n");
        printf("3. Display employee\n");
        printf("4. Exit\n");
        printf("Enter from 1 to 4:");
        scanf("%d",&n);
        if (n == 1)
        {
            create(buffer);
        }
        else if (n == 2)
        {
            del(buffer);
        }
        else if (n == 3)
        {
            display(buffer);
        }
    }while(n != 4);
    free(buffer);
    return 0;
}

void create(emp *buffer)
{
    size++;
    if (p != 0)
    {
        buffer = realloc(buffer, size * sizeof(emp));
        if (buffer == NULL)
        {
            printf("Error");
            exit(1);
        }
    }
    printf("Enter:");
    scanf("%s%s", (buffer + size - 1)->name, (buffer + size - 1)->company);
    p++;
}   

void del(emp *buffer)
{
    // deletes only last node
    size--;
    buffer = realloc(buffer, size * sizeof(emp));
    if (buffer == NULL)
    {
        printf("Error");
        exit(1);
    }
}

void display(emp *buffer)
{
    int k = 0;
    for (k = 1; k <= size; k++)
    {
        printf("Name:%s\n",(buffer + k - 1)->name);
        printf("Company:%s\n",(buffer + k - 1)->company);
    }
}

更新：我跑了valgrind并得到以下内容，但无法理解我在哪里错误地重新分配。

 ==3322== Invalid free() / delete / delete[] / realloc()
==3322==    at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3322==    by 0x4008C9: create (in /home/akshay/Data/practice/a.out)
==3322==    by 0x40081C: main (in /home/akshay/Data/practice/a.out)
==3322==  Address 0x5203040 is 0 bytes inside a block of size 40 free'd
==3322==    at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3322==    by 0x4008C9: create (in /home/akshay/Data/practice/a.out)
==3322==    by 0x40081C: main (in /home/akshay/Data/practice/a.out)
==3322==  Block was alloc'd at
==3322==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3322==    by 0x400786: main (in /home/akshay/Data/practice/a.out)
==3322== 
Error==3322== 
==3322== HEAP SUMMARY:
==3322==     in use at exit: 80 bytes in 1 blocks
==3322==   total heap usage: 5 allocs, 4 frees, 2,288 bytes allocated
==3322== 
==3322== LEAK SUMMARY:
==3322==    definitely lost: 80 bytes in 1 blocks
==3322==    indirectly lost: 0 bytes in 0 blocks
==3322==      possibly lost: 0 bytes in 0 blocks
==3322==    still reachable: 0 bytes in 0 blocks
==3322==         suppressed: 0 bytes in 0 blocks
==3322== Rerun with --leak-check=full to see details of leaked memory
==3322== 
==3322== For counts of detected and suppressed errors, rerun with: -v
==3322== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

Answer 1

您正在通过值将缓冲区传递给create和del，因此您所做的任何更改都不会被反映出来。因此free获得buffer的旧值。你有3个选择 -

O1：使缓冲区全局化，就像你对大小所做的那样，并且不要将它作为参数传递。容易但不建议。

O2：从buffer和del返回create的新值。然后在调用时执行

buffer = del(buffer);

O3：将指针传递给缓冲区而不是缓冲区并在其中进行修改。您的原型将更改为

void create(emp ** buffer);

您必须在*buffer内的每个位置使用create（del相同）。此外，通话将更改为

create(&buffer);

这有点复杂但是最正确的＆＃34;之一。

希望能帮助您理解这个问题。

用于动态分配在不同IDE上以不同方式运行的内存（基于结构）的程序

1 个答案: