s = (struct my_struct *)malloc(sizeof *s); 为什么struct my_struct *是指针
时间: 2024-11-26 11:07:37 浏览: 19
这段代码中`s = (struct my_struct *)malloc(sizeof *s);`是C语言里的一个常见操作,用于动态分配内存存储结构体`my_struct`。解释一下:
1. `struct my_struct`: 这是一个自定义的数据类型,即结构体,它可能是由若干不同类型的数据成员组成的。
2. `sizeof *s`: 这是一个表达式,它的含义是获取`s`所指向的结构体`my_struct`类型的大小,因为`*s`是一个未初始化的`my_struct`类型的指针,`sizeof`运算符会计算这个类型占用的空间。
3. `(struct my_struct *)`: 这部分是一个类型转换,将`malloc()`返回的结果从`void *`(通用指针类型)转换成`struct my_struct *`类型。这是因为`malloc()`函数总是返回一个通用的地址,通过类型转换确保我们得到的是可以存储`my_struct`实例的正确指针类型。
所以,`struct my_struct *`就是一个指向`my_struct`结构体的指针,通过它我们可以动态地创建并操作这个结构体的实例。
相关问题
#define _CRT_SECURE_NO_WARNINGS #include<stdio.h> #include<windows.h> #include<string.h> #include<stdlib.h> #include<math.h> #include<malloc.h> typedef struct character_name { char name[100]; struct character_name* next; }char_name; typedef struct character_title { char title[100]; struct character_title* next; }char_title; typedef struct character_identity { char identity[100]; struct character_identity* next; }char_iden; typedef struct character_attribute { int strength; struct character_attribute* next; }char_att; typedef struct character_information { char_name* _name; char_title* _title; char_iden* _iden; char_att* _att; struct character_information* next; }char_inf; char_inf* initialization() { char_inf* node = (char_inf*)malloc(sizeof(char_inf)); node->_name = (char_name*)malloc(sizeof(char_name)); node->_title = (char_title*)malloc(sizeof(char_title)); node->_iden = (char_iden*)malloc(sizeof(char_iden)); node->_att = (char_att*)malloc(sizeof(char_att)); return node; } char_inf* ceshi, * current, * end; char_name* name_current, * name_end; char_title* title_current, * title_end; char_iden* iden_current, * iden_end; char_att* att_current, att_end; int main() { ceshi = initialization(); name_current = (char_name*)malloc(sizeof(char_name)); name_current = ceshi->_name; strcpy(name_current->name, "ceshi_1_1"); name_current->next = (char_name*)malloc(sizeof(char_name)); name_current = name_current->next; strcpy(name_current->name, "ceshi_1_2"); strcpy(ceshi->_title->title, "ceshi_2"); strcpy(ceshi->_iden->identity, "ceshi_3"); ceshi->_att->strength = 4; name_current = ceshi->_name; while (name_current->next != NULL) { printf("%s\n", name_current->name); name_current = name_current->next; } printf("%s\n%s\n%d\n", ceshi->_title->title, ceshi->_iden->identity, ceshi->_att->strength); return 0; } 为什么提示我访问权限报错
在你的代码中,提示访问权限错误的原因是你错误地给指针变量`att_end`赋值。
在`main`函数中,你声明了一个指向`char_att`类型的指针变量`att_end`,然后你尝试给它赋值。但是,在赋值的过程中,你漏掉了`att_end`指针变量前面的`*`,导致赋值操作实际上是在修改指针变量本身的值,而不是修改它所指向的内存。
为了解决这个问题,你需要在赋值语句中正确地使用`*`来解引用指针,如下所示:
```c
*att_current = *att_end;
```
请注意,在之前的代码中,你没有为`att_end`分配内存空间,因此在这里直接解引用可能会导致未定义行为。如果你需要为`att_end`分配内存并进行赋值操作,请确保在操作之前为它分配足够的内存空间。
修正后的代码如下所示:
```c
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<windows.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<malloc.h>
typedef struct character_name
{
char name[100];
struct character_name* next;
} char_name;
typedef struct character_title
{
char title[100];
struct character_title* next;
} char_title;
typedef struct character_identity
{
char identity[100];
struct character_identity* next;
} char_iden;
typedef struct character_attribute
{
int strength;
struct character_attribute* next;
} char_att;
typedef struct character_information
{
char_name* _name;
char_title* _title;
char_iden* _iden;
char_att* _att;
struct character_information* next;
} char_inf;
char_inf* initialization()
{
char_inf* node = (char_inf*)malloc(sizeof(char_inf));
node->_name = (char_name*)malloc(sizeof(char_name));
node->_title = (char_title*)malloc(sizeof(char_title));
node->_iden = (char_iden*)malloc(sizeof(char_iden));
node->_att = (char_att*)malloc(sizeof(char_att));
return node;
}
int main()
{
char_inf* ceshi = initialization();
ceshi->_name->next = NULL;
strcpy(ceshi->_name->name, "ceshi_1_1");
ceshi->_name->next = (char_name*)malloc(sizeof(char_name));
strcpy(ceshi->_name->next->name, "ceshi_1_2");
strcpy(ceshi->_title->title, "ceshi_2");
strcpy(ceshi->_iden->identity, "ceshi_3");
ceshi->_att->strength = 4;
char_name* name_current = ceshi->_name;
while (name_current != NULL)
{
printf("%s\n", name_current->name);
name_current = name_current->next;
}
printf("%s\n%s\n%d\n", ceshi->_title->title, ceshi->_iden->identity, ceshi->_att->strength);
return 0;
}
```
修正后的代码中,我也对代码的其他部分进行了一些调整和修正,以确保正确的运行。
#define _CRT_SECURE_NO_WARNINGS #include<stdio.h> #include<windows.h> #include<string.h> #include<stdlib.h> #include<math.h> #include<malloc.h> typedef struct character_name { char name[100]; struct character_name* next; }char_name; typedef struct character_title { char title[100]; struct character_title* next; }char_title; typedef struct character_identity { char identity[100]; struct character_identity* next; }char_iden; typedef struct character_attribute { int strength; struct character_attribute* next; }char_att; typedef struct character_information { char_name* _name; char_title* _title; char_iden* _iden; char_att* _att; struct character_information* next; }char_inf; char_inf* initialization() { char_inf* node = (char_inf*)malloc(sizeof(char_inf)); node->_name = (char_name*)malloc(sizeof(char_name)); node->_title = (char_title*)malloc(sizeof(char_title)); node->_iden = (char_iden*)malloc(sizeof(char_iden)); node->_att = (char_att*)malloc(sizeof(char_att)); return node; } char_inf* ceshi, * current, * end; char_name* name_current, * name_end; char_title* title_current, * title_end; char_iden* iden_current, * iden_end; char_att* att_current, att_end; int main() { ceshi = initialization(); name_current = (char_name*)malloc(sizeof(char_name)); name_current = ceshi->_name; strcpy(name_current->name, "ceshi_1_1"); name_current->next = (char_name*)malloc(sizeof(char_name)); name_current = name_current->next; strcpy(name_current->name, "ceshi_1_2"); strcpy(ceshi->_title->title, "ceshi_2"); strcpy(ceshi->_iden->identity, "ceshi_3"); ceshi->_att->strength = 4; name_current = ceshi->_name; while (name_current->next != NULL) { printf("%s\n", name_current->name); name_current = name_current->next; } printf("%s\n%s\n%d\n", ceshi->_title->title, ceshi->_iden->identity, ceshi->_att->strength); return 0; } 中为什么在下面两段代码中报错 name_current = (char_name*)malloc(sizeof(char_name)); name_current = ceshi->_name; strcpy(name_current->name, "ceshi_1_1"); name_current->next = (char_name*)malloc(sizeof(char_name)); name_current = name_current->next; strcpy(name_current->name, "ceshi_1_2"); name_current = ceshi->_name; while (name_current->next != NULL) { printf("%s\n", name_current->name); name_current = name_current->next; }
在下面两段代码中报错的原因是你没有正确地为name_current分配内存空间。
首先,在这行代码中:
```c
name_current = (char_name*)malloc(sizeof(char_name));
```
你为name_current分配了内存空间,但是在接下来的一行代码中:
```c
name_current = ceshi->_name;
```
你又将name_current指向了ceshi->_name,这导致你刚刚分配的内存空间被覆盖了,造成内存泄漏。
解决这个问题的方法是,你可以直接将ceshi->_name赋给name_current,而不需要使用malloc来为name_current分配内存空间,修改后的代码如下:
```c
name_current = ceshi->_name;
strcpy(name_current->name, "ceshi_1_1");
name_current->next = (char_name*)malloc(sizeof(char_name));
name_current = name_current->next;
strcpy(name_current->name, "ceshi_1_2");
```
另外,在最后一段代码中,你需要检查name_current是否为NULL,否则可能会出现访问空指针的错误。修改后的代码如下:
```c
name_current = ceshi->_name;
while (name_current != NULL)
{
printf("%s\n", name_current->name);
name_current = name_current->next;
}
```
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