malloc和free动态变化的结构

我在动态变化的结构中移动指针时遇到了麻烦。 我已经创建了我的代码，你可以在malloc中获得更多的内存，这看起来很有效。 我遇到的问题是如何添加到结构，如何释放内存以及如何从结构移动到结构并打印所有项目。

我正在尝试测试添加和打印（删除function，似乎没有工作，segfaults）

当我添加到结构然后打印结构时，我从我添加的值中获得了一个段错误。 我不知道我是否正确地从第一个结构转移到下一个结构。

#include  #include  #include "pointer.h" /******************************************** Creates more memory for size (strut * rec+1) *********************************************/ employee *create(int record){ employee *new_employee = malloc(sizeof(employee) * (record+1)); return new_employee; } /******************************************** Copies the data from one structure to a new structure with size "structure" multipled by rec+1 ***********************************************/ employee *copy(employee *data, int record){ employee *new_employee = create(record); int i; for(i = 0; ifirst = data->first; new_employee->last = data->last; new_employee->start_date = data->start_date; new_employee->sal = data->sal; data++; } /******************** Needs to free the old struct *********************/ //deleteData(data, record); return new_employee; } /******************************************** Function prints everything in the struct *********************************************/ void printStruct(employee *data, int record){ int i; for(i = 0; ifirst, data->last); printf("The employee was hired on: %s\n", data->start_date); printf("The employee make $%f\n\n", data->sal); data++; } } /****************************************** Function frees the old data base *******************************************/ void deleteData(employee *data, int record){ int i; for(i = 0; ifirst); free(data->last); free(data->start_date); data++; } free(data); } /****************************************** Adds an employee to the new structure *******************************************/ employee *add(employee *data,char *fname, char *lname, char *date, float salary, int record){ employee *employeeDB = create(record); employeeDB = copy(data, record); int i; employeeDB++; employeeDB->first = fname; employeeDB->last = lname; employeeDB->start_date = date; employeeDB->sal = salary; return employeeDB; } /************************** Starts of the main function ***************************/ int main(void){ //Keeps track of the number of records that are in the structure int rec = 0; //Keeps the number of accesses to the structure. Even with the one entry the structure has not been accessed. int acc = 0; //Holds the input information for the menu int input; //holds the information for inputing user first name char *fname; //holds the information for inputing user last name char *lname; //holds the information for for the startdate char *start; //holds the information for the salary; float sal; /********************************* This next section adds an employee to the record ************************************/ //This creates the first entry to the dynamic structure. employee *first_employee = create(rec); first_employee->first = "FIRST"; first_employee->last = "LAST"; first_employee->start_date = "June-20th-2006"; first_employee->sal = 55555.55; //increase the number of records rec = rec+1; employee *new_employeeDB = add(first_employee, "fname", "lname", "JUNE-20th-2010", 55555.55, rec); rec = rec + 1; printStruct(new_employeeDB, rec); printf("%d\n", (sizeof(employee)* rec)); } 

Answer 1

第一个问题：好的……你没有提供员工类型的声明。 我猜第一个和最后一个被声明为char指针，这是一个错误。 你需要它们是固定大小的char数组，否则这将无法工作。 选择字符串的最大长度并声明结构如下。

 typedef struct { char name[50]; char surname[50]; .... } employee; 

上一篇文章：

好吧，我必须承认我不喜欢这种方式来实现这个东西。 我会使用更稳定的方法。

首先，由于它只是一个项目列表，您可以使用双向链表。 这将允许您添加和删除具有O（1）复杂度的元素。 确实很好。

这也允许您迭代从第一个到最后一个的所有项目。

为了做到这一点，我会使用更多面向OOP的方法:)我知道，我们在C但是听听这个想法。

 typedef struct { MyList* OwnerList; Employee* Previous; Employee* Next; char name[50]; int age; } Employee; typedef struct { Employee* First; Employee* Last; int Count; } MyList; MyList* AllocList() { return calloc(sizeof(MyList), 1); } void DeleteList(MyList* list) { Employee* current; Employee* next; for (current = list->First; current != NULL; current = next) { next = current->Next; free(current); } free(list); } int GetCount(const MyList* list) { return list->Count; } Employee* AddAmployee(MyList* list) { Employee* result = calloc(sizeof(Employee), 1); Employee* last = list->Last; if (last != null) last->Next = result; else list->First = result; result->Previous = last; list->Last = result; ++list->Count; result->OwnerList = list; return result; } void RemoveEmployee(Employee* employee) { /* i leave removal for you as exercise :) look for doubly linked list */ free(employee); } 

现在，迭代所有项目很简单：

 Employee* current; for (current = list->First; current != null; current = current->Next) printf("%s %d\n", current->name, current->age); 

Answer 2

您没有使用malloc来分配employee的first，last和start_date属性。 因此，当你在deleteData中的指针上调用free时，你就会破坏内存。 我还会考虑使用链表或其他数据结构（如数组）来保存员工记录，从而使您拥有更清晰的界面。