C中仍可访问的内存

Question

使用valgrind检查内存泄漏后，我得到以下结果。

HEAP SUMMARY:
==10299==   in use at exit: 2,286 bytes in 68 blocks
==10299==   total heap usage: 139 allocs, 71 frees, 164,646 bytes allocated
==10299== 
==10299== LEAK SUMMARY:
==10299==    definitely lost: 0 bytes in 0 blocks
==10299==    indirectly lost: 0 bytes in 0 blocks
==10299==      possibly lost: 0 bytes in 0 blocks
==10299==    still reachable: 2,286 bytes in 68 blocks
==10299==         suppressed: 0 bytes in 0 blocks
==10299== Reachable blocks (those to which a pointer was found) are not shown.
==10299== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==10299== 
==10299== For counts of detected and suppressed errors, rerun with: -v
==10299== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

我的目的是尝试使其不可能发生内存泄漏。 我知道使用malloc函数后必须释放内存。 但是即使如此，它仍然给我相同的结果。 因此，我需要帮助才能看到我的编码有什么问题。

下面是我的代码。

 struct date
{   int day;
    int month;
    int year;
};

Date *date_create(char *datestr)
{       
    //declare Date to pointer from datestr and check the data size of Date
    Date *pointer = (Date *) malloc (sizeof(Date));

    if(pointer!=NULL)
    {
        scanf(datestr,"%2d/%2d/%4d",pointer->day,pointer->month,pointer->year);
    }
        else
    {
          printf("Error! ");
      date_destroy(pointer);

    }
        return pointer;

}

void date_destroy(Date *d)
{

    free(d);
}


int main(){
return 0;
    }

Answer 1

如果从main调用函数，则valgrind将在代码中显示内存泄漏。 您不应该转换malloc。 如果您已经成功分配了内存，则只有您可以释放它。 您需要像这样更改代码

Date *date_create(char *datestr)
{       
    //declare Date to pointer from datestr and check the data size of Date
    Date *pointer =  malloc (sizeof (Date));

    if(pointer!=NULL)
    {
        scanf(datestr,"%2d/%2d/%4d",pointer->day,pointer->month,pointer->year);
    }
        else
    {
          printf("Error! ");
     // date_destroy(pointer); Not required

    }
    if(pointer) { // Free the allocated memory after use
        date_destroy(pointer); 
    }
        return pointer;

}

Answer 2

当malloc返回NULL ，您的代码被设置为free指针，但是free(NULL)不执行任何操作。

使用完指针后，需要调用free() 。

int main(void) {
    char datestr[64];
    Date* dptr;

    fgets(datestr, sizeof(datestr), stdin);

    dptr = date_create(datestr);

    /* do some stuff with Date ptr */

    free(dptr); /* now call free */

    return 0;
}

另外，在您认为我想使用sscanf时，在date_create()函数中使用scanf 。

所以这条线

scanf(datestr,"%2d/%2d/%4d",pointer->day,pointer->month,pointer->year);

变成

sscanf(datestr,"%2d/%2d/%4d",pointer->day,pointer->month,pointer->year);