如何正确安全地释放（）使用C中嵌套结构的所有内存？ [英] How to correctly and safely free() all memory used a nested struct in C?
问题描述
我嵌套了四个不同的结构层。代码如下：
typedef struct System system;
typedef struct College大学；
typedef struct学生学生；
typedef struct Family家庭；
#define MAX_COLLEGES 10
#define MAX_NAME_LEN 32
#define MAX_STUDENTS 10
结构系统{
college * Colleges [MAX_COLLEGES];
};
struct College {
char name [MAX_NAME_LEN];
学生*学生[MAX_STUDENTS]；
};
结构学生{
字符名称[MAX_NAME_LEN]；
int id;
家庭*家族； //是错别字
};
struct Family {
char parentName [MAX_NAME_LEN];
char motherName [MAX_NAME_LEN];
};
然后我为所有这些人分配了内存（不确定是否正确分配了所有人），如下所示：
system * collegeSys = malloc（sizeof（system））;
大学*学院= malloc（sizeof（college））;
学生*学生= malloc（sizeof（学生））;
family * fam = malloc（sizeof（family））;
//然后是初始化
...
...
...
现在，我需要删除 collegeSys 结构以及与其关联的所有内容。因此，我不知道是否可以仅释放第一个 collegeSys 结构而不释放任何其他结构，例如：
免费（collegeSys）;
或者为了删除与之相关的任何内容，我必须自下而上释放所有内容，像这样：
免费（家庭）；
免费（学生）；
免费（大学）；
free（collegeSys）;
或者为此，我什至必须释放每个结构体中包含的所有内容并自底向上释放它们，就像这样：
免费（fam-> FatherName）；
免费（fam-> motherName）；
免费（fam）；
免费（学生->名称）；
免费（学生-> id）；
免费（学生-> fam）；
免费（学生）
。
。直到
。
免费（collegeSys->大学）；
免费（collegeSys）；
哪个是释放内存的正确和安全的方法？还是它们都不是？
我不太了解具有指针数组的意义，可以用指针来完成。
定义：
struct系统{
大学*学院；
};
struct College {
char name [MAX_NAME_LEN];
学生*学生；
};
结构学生{
字符名称[MAX_NAME_LEN]；
int id;
家族*家族；
};
struct Family {
char parentName [MAX_NAME_LEN];
char motherName [MAX_NAME_LEN];
};
分配和初始化：
system * collegeSys = malloc（sizeof（* collegeSys））;
collegeSys-> colleges = malloc（MAX_COLLEGES * sizeof（*（collegeSys-> colleges））））;
collegeSys-> colleges->学生= malloc（MAX_STUDENTS * sizeof（*（collegeSys-> colleges->学生））））;
collegeSys-> colleges-> students-> fam = malloc（sizeof（*（collegeSys-> colleges-> students-> fam）））;
释放：
免费（collegeSys-> colleges->学生-> fam）；
免费（collegeSys-> colleges->学生）；
free（collegeSys-> colleges）;
free（collegeSys）;
更新：
就像我想让结构学生A，B，C，D属于结构学院
collegeSys-> colleges-> students [0] = A;
collegeSys-> colleges-> students [1] = B;
collegeSys-> colleges-> students [2] = C;
collegeSys-> colleges-> students [3] = D;
应该这样做。
如果具有 student 的数组，您可以使用 memcpy 或在 loop 。
结构学生stud [MAX_STUDENTS] = {...};
memcpy（collegeSys-> colleges-> students [2]，stud，MAX_STUDENTS）;
或
for（int i = 0; i< MAX_STUDENTS; i ++）
collegeSys-> colleges-> students [i] = stud [i];
注意：
在这种情况下，您可以将数组分配给 collegeSys-> colleges->学生动态内存分配或释放。
// collegeSys-> colleges-> students = malloc（MAX_STUDENTS * sizeof（*（ collegeSys->学院->学生）））； //泄漏记忆
collegeSys-> colleges-> students = stud;
//免费（collegeSys-> colleges->学生）; //错误的
I have four different layers of struct nested. The code is as follows:
typedef struct System system;
typedef struct College college;
typedef struct Student student;
typedef struct Family family;
#define MAX_COLLEGES 10
#define MAX_NAME_LEN 32
#define MAX_STUDENTS 10
struct System {
college *Colleges[MAX_COLLEGES];
};
struct College {
char name[MAX_NAME_LEN];
student *Students[MAX_STUDENTS];
};
struct Student {
char name[MAX_NAME_LEN];
int id;
family *fam; //was typo familiy
};
struct Family {
char fatherName[MAX_NAME_LEN];
char motherName[MAX_NAME_LEN];
};
And I allocated memory to all of them (I'm not sure if I allocated all of them correctly), as follows:
system *collegeSys = malloc(sizeof(system));
college *colleges = malloc(sizeof(college));
student *students = malloc(sizeof(student));
family *fam = malloc(sizeof(family));
// then the following is initialization
...
...
...
Now, I need to delete the collegeSys structure and anything associated with it. So, I don't know if I can just free the first collegeSys struct without freeing any other structs, like this:
free(collegeSys);
Or in order to "delete anything associated with it", I have to free everything bottom-up, like this:
free(fam);
free(students);
free(colleges);
free(collegeSys);
Or to that end, I even have to free anything included inside each struct and free them bottom-up, like this:
free (fam -> fatherName);
free (fam -> motherName);
free (fam);
free (students -> name);
free (students -> id);
free (students -> fam);
free (students)
.
. till
.
free (collegeSys -> colleges);
free (collegeSys);
Which one is the correct and safe way to free the memory? Or none of them is?
I don't really understand point of having array of pointers, it could be done with pointer.
Definition:
struct System {
college *Colleges;
};
struct College {
char name[MAX_NAME_LEN];
student *Students;
};
struct Student {
char name[MAX_NAME_LEN];
int id;
familiy *fam;
};
struct Family {
char fatherName[MAX_NAME_LEN];
char motherName[MAX_NAME_LEN];
};
Allocation and initialization :
system *collegeSys = malloc(sizeof(*collegeSys));
collegeSys->colleges = malloc(MAX_COLLEGES * sizeof(*(collegeSys->colleges)));
collegeSys->colleges->students = malloc(MAX_STUDENTS * sizeof(*(collegeSys->colleges->students)));
collegeSys->colleges->students->fam = malloc(sizeof(*(collegeSys->colleges->students->fam)));
Freeing:
free(collegeSys->colleges->students->fam);
free(collegeSys->colleges->students);
free(collegeSys->colleges);
free(collegeSys);
Update:
Like I want to have struct student A, B, C, D under a struct college
collegeSys->colleges->students[0] = A;
collegeSys->colleges->students[1] = B;
collegeSys->colleges->students[2] = C;
collegeSys->colleges->students[3] = D;
Should do it.
If yo have array of students you can use memcpy or copy in loop.
struct student stud[MAX_STUDENTS] = {...};
memcpy(collegeSys->colleges->students[2], stud, MAX_STUDENTS);
or
for (int i = 0; i< MAX_STUDENTS; i++)
collegeSys->colleges->students[i] = stud[i];
Note:
You can assign the array to collegeSys->colleges->students in that case you don't need dynamic memory allocation or freeing.
// collegeSys->colleges->students = malloc(MAX_STUDENTS * sizeof(*(collegeSys->colleges->students))); //Leaks memory
collegeSys->colleges->students = stud;
//free(collegeSys->colleges->students); //wrong
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