此笔记由个人整理
塞上苍鹰_fly
课程来自：尚观C
一、动态内存
void *malloc(size_t size
);
void free(void *ptr
);
void *calloc(size_t nmemb
,size_t size
);
void *realloc(void *ptr
,size_t size
);
案例：申请空间与释放空间
#include "stdio.h"
#include "stdlib.h"
int main()
{
int *p
= NULL;
p
= (int *)malloc(sizeof(int));
if(p
== NULL)
{
printf("malloc() error!!\n");
exit(1);
}
*p
= 10;
printf("%p-->%d\n",*p
,*p
);
free(p
);
*p
= 123;
printf("%p-->%d\n",*p
,*p
);
exit(0);
}
free是通过之前使用的指针不能再去到之前所指向的地址
free后不要在继续使用之前定义的空间，会产生野指针，容易出现不必要的错误
结果（windows）
案例：动态变长数组
#include "stdio.h"
#include "stdlib.h"
int main()
{
int *p
= NULL;
int num
= 5;
int i
;
p
= malloc(sizeof(int) * num
);
for(i
= 0;i
< num
;i
++)
scanf("%d",&p
[i
]);
for(i
= 0;i
< num
;i
++)
printf("%d",p
[i
]);
printf("\n");
exit(0);
}
结果
案例：传参避免内存泄露
#include "stdio.h"
#include "stdlib.h"
void func(int **p
,int n
)
{
*p
= malloc(n
);
if(*p
== NULL)
exit(1);
return ;
}
int main()
{
int *p
= NULL;
int num
= 100;
func(&p
,num
);
free(p
);
exit(0);
}
#include "stdio.h"
#include "stdlib.h"
void *func(int *p
,int n
)
{
p
= malloc(n
);
if(p
== NULL)
exit(1);
return p
;
}
int main()
{
int *p
= NULL;
int num
= 100;
p
= func(&p
,num
);
free(p
);
exit(0);
}
二、优化学生信息管理系统
替换结构体成员变量name为*name
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#define NAMEMAX 1024
struct student_st
{
int id
;
char *name
;
int math
;
int chinese
;
};
void menu(void)
{
printf("********************************\n");
printf("1 set\n2 change name\n3 show\n");
printf("********************************\n");
}
void stu_set(struct student_st
*p
,const struct student_st
*q
)
{
p
->id
= q
->id
;
p
->name
= malloc(strlen(q
->name
)+1);
if(p
->name
== NULL)
exit(1);
strcpy(p
->name
,q
->name
);
p
->math
= q
->math
;
p
->chinese
= q
->chinese
;
}
void stu_show(struct student_st
*p
)
{
printf("%d %s %d %d\n",p
->id
,p
->name
,p
->math
,p
->chinese
);
}
void stu_changename(struct student_st
*p
,const char *newname
)
{
free(p
->name
);
p
->name
= malloc(strlen(newname
)+1);
strcpy(p
->name
,newname
);
}
int main()
{
int choice
;
int ret
;
char newname
[NAMEMAX
];
struct student_st stu
;
struct student_st tmp
;
menu();
do
{
printf("\nPlease enter num(q for quit):");
ret
= scanf("%d",&choice
);
if(ret
!= 1)
break;
switch(choice
)
{
case 1:
tmp
.name
= malloc(NAMEMAX
);
printf("Please enter for the stu[id name math chinese]:");
scanf("%d %s %d %d",&tmp
.id
,&tmp
.name
,&tmp
.math
,&tmp
.chinese
);
stu_set(&stu
,&tmp
);
break;
case 2:
printf("Please enter the newname:");
scanf("%s",newname
);
stu_changename(&stu
,newname
);
break;
case 3:
stu_show(&stu
);
break;
default:
exit(1);
}
}while(1);
exit(0);
}
三、typedef
为已有的数据类型改名
typedef 已有的数据类型 新名字
案例
#include "stdio.h"
#include "stdlib.h"
typedef int INT
;
int main()
{
INT i
= 100;
printf("%d\n",i
);
exit(0);
}
结果
typedef用法
#define INT int
typedef int INT;
INT i; --> int i;
---------------------------------------
#define IP int *
typedef int IP;
IP p,q; --> int *p,q;
IP p,q; --> int *p,*q;
----------------------------------------
typedef int ARR[6]; --> int [6] ->ARR;
ARR a; --> int a[6];
----------------------------------------
struct node_st{
};
typedef struct node_st NODE;
NODE a; -> struct node_st a;
NODE *P;-> struct node_st *p;
typedef struct node_st *NODEP;
NODEP p; -> struct node_st *p;
----------------------------------------
typedef struct
{
int i;
float f;
}NODE,*NODEP;
----------------------------------------
typedef int FUNC(int); --> int(int) FUNC;
FUNC F; -> int f(int);
typedef int *FUNCP(int);
FUNC p; ---> int *p(int);
typedef int *(*FUNCP)(int);
FUNC p; --> int *(*p)(int);
案例
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#define NAMEMAX 1024
typedef struct student_st
{
int id
;
char *name
;
int math
;
int chinese
;
}STU
;
void menu(void)
{
printf("********************************\n");
printf("1 set\n2 change name\n3 show\n");
printf("********************************\n");
}
void stu_set(STU
*p
,const STU
*q
)
{
p
->id
= q
->id
;
p
->name
= malloc(strlen(q
->name
)+1);
if(p
->name
== NULL)
exit(1);
strcpy(p
->name
,q
->name
);
p
->math
= q
->math
;
p
->chinese
= q
->chinese
;
}
void stu_show(STU
*p
)
{
printf("%d %s %d %d\n",p
->id
,p
->name
,p
->math
,p
->chinese
);
}
void stu_changename(STU
*p
,const char *newname
)
{
free(p
->name
);
p
->name
= malloc(strlen(newname
)+1);
strcpy(p
->name
,newname
);
}
int main()
{
int choice
;
int ret
;
char newname
[NAMEMAX
];
STU stu
;
STU tmp
;
menu();
do
{
printf("\nPlease enter num(q for quit):");
ret
= scanf("%d",&choice
);
if(ret
!= 1)
break;
switch(choice
)
{
case 1:
tmp
.name
= malloc(NAMEMAX
);
printf("Please enter for the stu[id name math chinese]:");
scanf("%d %s %d %d",&tmp
.id
,&tmp
.name
,&tmp
.math
,&tmp
.chinese
);
stu_set(&stu
,&tmp
);
break;
case 2:
printf("Please enter the newname:");
scanf("%s",newname
);
stu_changename(&stu
,newname
);
break;
case 3:
stu_show(&stu
);
break;
default:
exit(1);
}
}while(1);
exit(0);
}
