C 结构体的定义
#include <stdio.h>
struct student
{
int ID;
char name[10];
int age;
}; //注意这里的分号
int main()
{
// 初始化
struct student student1 = {1111,"Redhat",20};
struct student student2 = {.ID = 1111,.name = "Debian",.age = 20};//C99才有
struct student student3 = {1111,"BSD",.ID = 20,.age = 30}; //ID = 20
//使用
printf("%d,%s,%d \n",student1.ID,student1.name,student1.age);
printf("%d,%s,%d \n",student2.ID,student2.name,student2.age);
printf("%d,%s,%d \n",student3.ID,student3.name,student3.age);
}
chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out
1111,Redhat,20
1111,Debian,20
20,BSD,30
结构体内存分配情况
小的遵循大的数据类型，存在浪费内存的情况
#include <stdio.h>#include <string.h>struct student{ unsigned char c1; unsigned char c2; unsigned int i1; unsigned char c3; unsigned char c4; unsigned char c5; unsigned char c6; unsigned int i2;}; int main(){ printf("%ld \n",sizeof(struct student)); struct student student1; memset(&student1,0x55,sizeof(struct student)); student1.i1 = 0x12345678; student1.i2 = 0x23456789; student1.c1 = 0x21; student1.c2 = 0x22; student1.c3 = 0x23; student1.c4 = 0x24; student1.c5 = 0x25; student1.c6 = 0x26; int *p = (int*) &student1; for(int i = 0;i< sizeof(struct student)/4;i++) { printf("%p %x \n",p,*p); p++; }}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out16 0x7ffc7913b1c0 55552221 0x7ffc7913b1c4 12345678 0x7ffc7913b1c8 26252423 0x7ffc7913b1cc 23456789 可以看到内存初始化就是0X55，第一个的4个字节存在了浪费
结构体，自定义数据类型：
#include <stdio.h>#include <string.h>struct student{ unsigned char c1:1; unsigned char c2:3; unsigned char c3:4;}; int main(){ printf("%ld \n",sizeof(struct student)); struct student student1; student1.c1 = 1; student1.c2 = 6; student1.c3 = 14; char *p = (char *)& student1; printf("%x,%d,%d,%d \n",*p,student1.c1,student1.c2,student1.c3);}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out1 ffffffed,1,6,14
结构体嵌套：
#include <stdio.h>#include <string.h>struct man{ unsigned char age;};struct student{ unsigned char name[20]; struct man a_man;}; int main(){ printf("%ld \n",sizeof(struct student)); struct student student1; student1.a_man.age = 10; printf("student age = %d \n",student1.a_man.age);}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out21 student age = 10
结构体数组，结构体嵌套
#include <stdio.h>#include <string.h>struct man{ char name[20]; unsigned char age; unsigned char heiget;};struct human{ struct man son; int money;};int main(){ printf("%ld \n",sizeof(struct human)); /* 结构体数组 */ struct man people[3]={ {"奥巴马",50,170}, {"金正恩",44,166}, {"朴槿惠",33,155}, }; /* 结构体嵌套 */ struct human a_human; a_human.son.age = 10; printf("son age = %d \n",a_human.son.age);}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out28 son age = 10
结构体赋值
#include <stdio.h>#include <string.h>struct man{ char name[20]; unsigned char age; unsigned char height;};int main(){ struct man people1={"奥巴马",50,170}; struct man people2; people2 = people1; //结构体的赋值,people1的内存赋值到了people2,二者相互独立！ //memcpy(&people2,&people1,sizeof(people1)); //相当于memcpy(&people2,&people1,sizeof(people1)); printf("%s,%d,%d \n",people2.name,people2.age,people2.height); /////////////////////////////////////////////////////// /*区别于数组 char str1[10] = {"Hello!"}; char str2[20]; str2 = str1; //这是不允许的。数组的名仅是一个地址，不允许赋值。 ////////////////////////////////////////////////////// //这个不是赋值，这个只能是指向了那个地址 char str3[] = {"Hello !"}; char *p1 = str3; char *p2 = p1; */}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out奥巴马,50,170
结构体赋值里面的指针变量
#include <stdio.h>#include <stdlib.h>#include <string.h>struct man{char *name;unsigned char age;unsigned char height;};int main() {struct man people1={"朴槿惠",40,170};struct man people2;people2 = people1;//结构体赋值printf("%s,%d,%d \n",people2.name,people2.age,people2.height);people2.name = "王麻子"; //指针指向常量"王麻子"printf("%s,%d,%d \n",people2.name,people2.age,people2.height);/*结构体指针*/struct man people3;people3.name = malloc(20);strcpy(people3.name,"孙悟空");printf("%s,%d,%d \n",people3.name,people3.age,people3.height);//free(people3.name); //堆释放会对下面的strcpy(people4.name,people3.name);有影响/*如果结构体里面有指针，不能通过简单赋值完成操作,因为指向的是一样的*/struct man people4;people4.name = malloc(strlen(people3.name)+1);strcpy(people4.name,people3.name);people4.age = people3.age;people4.height = people3.height;printf("%s,%d,%d \n",people4.name,people4.age,people4.height);free(people3.name); //堆释放 free(people4.name); //堆释放 }chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out朴槿惠,40,170 王麻子,40,170 孙悟空,0,0 孙悟空,0,0
结构体指针 初步1
#include <stdio.h>#include <stdlib.h>#include <string.h>struct man{ char *name; unsigned char age; unsigned char height;};int main(){ struct man people1; struct man *people2 = &people1; (*people2).name = malloc(10); (*people2).age = 20; (*people2).height = 170; /* 上面的形式可以写成一下：*/ people2 -> name = malloc(10); people2 -> age = 20; people2 -> height = 170;}编译通过chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outchunli@ubuntu:~/pointer$
结构体指针 初步2
#include <stdio.h>#include <stdlib.h>#include <string.h>struct man{ unsigned char id; char name[20]; unsigned char height;};int main(){ struct man people[3] = { {1,"wang",181}, //wang属于常量 {2,"li",182}, {3,"zhang",189}, }; /* 定义一个结构体指针 */ struct man *people2 = &people[0]; printf("%d,%s,%d \n",people2->id,people2->name,people2->height); /* 访问方式2,也可以方便for循环 */ printf("%d,%s,%d \n",people2[1].id,people2[1].name,people2[1].height); people2++;//一次会移动一个结构体 printf("%d,%s,%d \n",people2->id,people2->name,people2->height); /* struct man people1 = {1,"wang",181}; struct man people2 = {2,"wang",181}; struct man people3 = {3,"wang",181}; 不要尝试用循环来遍历这样的数据，因为您不知道编译器是怎么安排的 最好放在同一个数组里面 */}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out1,wang,181 2,li,182 2,li,182
结构体的指针，初步3
#include <stdlib.h>#include <string.h>struct man{ unsigned char id; char *name; unsigned char age;};int main(){ struct man *sp = malloc(sizeof(struct man)); sp->id = 5; sp->age = 10; sp->name = malloc(10); strcpy(sp->name,"zhang"); printf("%d,%s,%d \n",sp->id,sp->name,sp->age); free(sp->name); // 一定先释放这个 free(sp); //要不然sp-name永远找不到了 return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out5,zhang,10
动态获取用户输入，不会浪费内存空间
#include <stdio.h>#include <stdlib.h>#include <string.h>struct test{char *name; //指针哦};struct man{unsigned char id;char *name;unsigned char age;//struct test *p; //有嵌套了一层，这是很难搞的};int main() {struct man *sp = malloc(sizeof(struct man) * 10);memset(sp,0,sizeof(struct man) * 10);// 内存清零for(int i = 0;i<10;i++){sp[i].id = i;sp[i].age = i;char buf[999]={0};scanf("%s",buf);int len = strlen(buf);sp[i].name =malloc(len+1) ;sprintf(sp[i].name,"%s",buf);}for(int i = 0;i<10;i++){printf("%d,%s,%d \n",sp[i].id,sp[i].name,sp[i].age);}for(int i = 0;i<10;i++)//循环释放{free(sp[i].name);}free(sp); //全部释放return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out1211111111111111111111111111111111111111111111111111111111111111111112222222222222222222222222222222222222222222222222222222222222222222aswsswdwdwdwdwedfwefefvdvgdf,kvdfvdfvdvmdvmmcsfdmcdsmc'nv vnvpmvpwvm[sdvfsdv dvdf e fdf f0,12,0 1,1111111111111111111111111111111111111111111111111111111111111111111,1 2,2222222222222222222222222222222222222222222222222222222222222222222,2 3,a,3 4,s,4 5,wsswdwdwdwdwedfwefefvdvgdf,kvdfvdfvdvmdvm,5 6,mcsfdmcdsmc'nv,6 7,vnvpmvpwvm[sdv,7 8,fsdv,8 9,dvdf,9
形参是结构体的函数
#include <stdio.h>#include <stdlib.h>#include <string.h>struct man{ unsigned char id; char *name; unsigned char age;};void fun1(struct man a_man){ printf("id = %d,age = %d,name = %s \n",a_man.id,a_man.age,a_man.name); strcpy(a_man.name,"haha"); //会影响传过来的数据,因为指向的是同一块内存 a_man.id = 99; //而id就不会发生变化 }int main() { //struct man people1 = {0,"wang",100}; struct man people1; people1.id = 0; people1.age = 10; people1.name = malloc(10); strcpy(people1.name,"wang"); fun1(people1); printf("id = %d,age = %d,name = %s \n",people1.id,people1.age,people1.name); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outid = 0,age = 10,name = wang id = 0,age = 10,name = haha
结构体参数，地址与传值
chunli@ubuntu:~/pointer$ cat main.c #include <stdio.h>#include <stdlib.h>#include <string.h>struct man{unsigned char id;char name[100];unsigned char age;};void fun1(struct man a_man)//传值过来{printf("id = %d,age = %d,name = %s \n",a_man.id,a_man.age,a_man.name);strcpy(a_man.name,"haha"); //无法修改a_man.id = 99; //无法修改}void fun2(struct man *sp) //地址传过来 //void fun2(const struct man *sp) //保护起来，防止修改{printf("id = %d,age = %d,name = %s \n",sp->id,sp->age,sp->name);strcpy(sp->name,"鲁智深"); //可以修改sp->id = 66; //可以修改}int main() {struct man people1;people1.id = 0;people1.age = 10;strcpy(people1.name,"wang");fun1(people1);//fun1无法修改参数值printf("id = %d,age = %d,name = %s \n",people1.id,people1.age,people1.name);fun2(&people1);printf("id = %d,age = %d,name = %s \n",people1.id,people1.age,people1.name);return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outid = 0,age = 10,name = wang id = 0,age = 10,name = wang id = 0,age = 10,name = wang id = 66,age = 10,name = 鲁智深
如何修改机构体内部的数组
#include <stdio.h>#include <stdlib.h>#include <string.h>struct str{char buf[100];};void fun1(struct str s){strcpy(s.buf,"hello "); }void fun2(char s[]){strcpy(s,"hello"); }int main() {struct str s={"world!"}; ;fun1(s);//传结构体，相当于赋值过去了，不会改变变量 (会很消耗内存的性能)printf("%s \n",s.buf);char s1[100]="world!";fun2(s1);//数组会把地址传过去，会修改变量printf("%s \n",s1);return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outworld! hello
结构体函数 初始化结构体
#include <stdio.h>#include <stdlib.h>#include <string.h>struct str{ char buf[100];};struct str getstr(){ struct str s; strcpy(s.buf,"Hello World!"); return s;}char *getstr1(){ char buf[100];//在栈区 strcpy(buf,"Hello World!"); //return buf;//无法返回有效数据}int main() { //char *tmp = getstr1(); 非法执行 struct str tmp = getstr(); printf("%s \n",tmp.buf); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outHello World!
【指向结构体的指针】
返回结构体，消耗很大
#include <stdio.h>#include <stdlib.h>#include <string.h>struct str{ char buf[100];};struct str getstr(){ struct str s; strcpy(s.buf,"Hello World!"); return s;}char *getstr1(){ char buf[100];//在栈区 strcpy(buf,"Hello World!"); //return buf;//无法返回有效数据}int main(){ //char *tmp = getstr1(); 非法执行 struct str tmp = getstr(); //内存拷贝，消耗很大 printf("%s \n",tmp.buf); return 0;}
返回结构体指针，消耗很小
#include <stdio.h>#include <stdlib.h>#include <string.h>struct str{ char buf[100];};struct str *getstr(){ struct str *s = malloc(sizeof(struct str)); printf("%p \n",s); strcpy(s->buf,"Hello World!"); return s;//把指针返回去}int main() { struct str *tmp = getstr(); //内存拷贝，消耗很大 printf("%p \n",tmp); printf("%s \n",tmp->buf); free(tmp); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out0x8cc010 0x8cc010 Hello World!
联合体初步1
#include <stdio.h>#include <stdlib.h>#include <string.h>union var{char c;int i;short d;char *s;//很危险};struct str{char c;int i;short d;};int main() {/*结构体与联合体元素地址区别*/union var v;//联合体元素公用用一个地址printf("%p \n" ,&(v.c));printf("%p \n" ,&(v.i));printf("%p \n" ,&(v.d));//小端对齐，高位放高位，低位放低位struct str s;//结构体，元素分别独立printf("%p \n" ,&(s.c));printf("%p \n" ,&(s.i));printf("%p \n" ,&(s.d));/*修改联合体元素*/printf("%ld \n",sizeof(v));v.c = 100;printf("%d \n",v.c); v.i = 1;printf("%d \n",v.c);return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out0x7ffc3f56e5d0 0x7ffc3f56e5d0 0x7ffc3f56e5d0 0x7ffc3f56e5e0 0x7ffc3f56e5e4 0x7ffc3f56e5e8 8 100 1
枚举
#include <stdio.h>#include <stdlib.h>#include <string.h>enum spectrum {red,yellow,green,blue,white,black};//申明一个枚举enum number {zero=10,one=9,two,three};//申明一个枚举void test(int i) {printf("test \n");}void test1(int a,int b) {printf("test1\n");}void test2(int a,int b,int c) {printf("test2\n");}void *function_factory(enum number n){ if(n == zero) return test; if(n == one) return test1; if(n == two) return test2;}void getcolor(enum spectrum color){ if(color == red) printf("red \n"); if(color == yellow) printf("yellow \n"); if(color == green) printf("green \n"); if(color == blue) printf("blue \n");}int main() { enum number b = one; void *p = function_factory(b); printf("%p ,%p \n",p,test1); enum spectrum color = red; getcolor(color); printf("%d,%d,%d \n",red,yellow,green); printf("%d,%d,%d \n",zero,one,two); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out0x400594 ,0x400594 red 0,1,2 10,9,10
typedef 初步
#include <stdio.h>#include <stdlib.h>#include <string.h>typedef unsigned char BYTE;#define mybyte unsigned chartypedef unsigned int UINT;//严格检查变量类型#define MAX 100 //简单替换，不做变量类型检查，没有分号struct student{ int id; char name[100];};int main() { BYTE b1 = 0xff; printf("%x \n",b1); UINT u1 = 0xFF00FF00; printf("%x \n",u1); //正常使用 struct student student1; //typedef 来定义 typedef struct student STUDENT; //自定义 数据类型 STUDENT student2; return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outff ff00ff00
没有用typedef之前的代码，看着很晕
#include <stdio.h>#include <stdlib.h>#include <string.h>const char *func1(const char *str1,const char *str2){ char *p = malloc(strlen(str1) + strlen(str2) +1); strcpy(p,str1); strcat(p,str2); return p;}const char *func2(const char *(*p)(const char *str1,const char *str2),const char *s1,const char *s2){ return p(s1,s2);}int main() { const char *tmp1 = "Hello"; const char *tmp2 = "world!"; const char *s = func2(func1,tmp1,tmp2); printf("%s \n",s); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outHelloworld!
typedef优化 对比
#include <stdio.h>#include <stdlib.h>#include <string.h>//定义一个指向这种函数类型的指针typedef const char *(*FUNC1)(const char *str1,const char *str2);const char *func1(const char *str1,const char *str2){ char *p = malloc(strlen(str1) + strlen(str2) +1); strcpy(p,str1); strcat(p,str2); return p;}const char *func2(FUNC1 p,const char *s1,const char *s2){ return p(s1,s2);}int main() { const char *tmp1 = "Hello"; const char *tmp2 = "world!"; const char *s = func2(func1,tmp1,tmp2); printf("%s \n",s); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outHelloworld!
typedef深入1
#include <stdio.h>#include <stdlib.h>#include <string.h>//定义一个指向这种函数类型的指针 的数据类型typedef const char *(*FUNC1)(const char *str1,const char *str2);//这是函数的原始申明const char *func1(const char *str1,const char *str2){ char *p = malloc(strlen(str1) + strlen(str2) +1); strcpy(p,str1); strcat(p,str2); return p;}const char *func2(FUNC1 p,const char *s1,const char *s2){ return p(s1,s2);}FUNC1 test(){FUNC1 tmp = func1;return tmp;}int main() {//定义10个FUNC1数据类型FUNC1 f[10];//定义一个数组10个元素，参数是const char *str1,const char *str2，返回值是 const char *const char *(*p[10])(const char *str1,const char *str2); const char *tmp1 = "Hello "; const char *tmp2 = "world!"; const char *s = func2(func1,tmp1,tmp2); printf("%s \n",s); return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outHello world!
超级复杂的typedef
chunli@ubuntu:~/pointer$ cat main.c #include <stdio.h>#include <stdlib.h>#include <string.h>typedef unsigned char BYTE;typedef unsigned int UINT;#define MYBYTE unsigned char#define MAX 100//typedef 100 MYMAX;struct student{int ID;char name[MAX];};typedef struct student STUDENT;typedef const char *(*FUNC1)(const char *str1, const char *str2);const char *func1(const char *str1, const char *str2){char *p = malloc(strlen(str1) + strlen(str2) + 1);strcpy(p, str1);strcat(p, str2);return p;}/*const char *(*)(const char *str1, const char *str2) test(){FUNC1 tmp = func1;return tmp;}*/const char *func2(const char *(*p[])(const char *str1, const char *str2), const char *s1, const char *s2){return (p[0])(s1, s2);}int main(){FUNC1 f[10];//const char *tmp1 = "hello ";const char *tmp2 = "world";f[0] = func1;const char *s = func2(f, tmp1, tmp2);printf("s = %s\n", s);BYTE b;b = 0x12;UINT i;i = 0xffff;STUDENT st;return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outs = hello worldchunli@ubuntu:~/pointer$
【复习================================】
联合体的指针，很危险
#include <stdio.h>#include <stdlib.h>#include <string.h>union var{char c;int i;short d;char *s;//很危险}; int main() {union var v;v.s = (char *)malloc(100);v.c = 1;free(v.s);//致命错误！ return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.outSegmentation fault (core dumped)
typedef 特别高级的用法
chunli@ubuntu:~/pointer$ cat main.c #include <stdio.h>#include <stdlib.h>#include <string.h>typedef struct student ST;struct student{char name[200];int id;};typedef const char *(*FUNC1)(const char *str1,const char *str2) ;const char *funcl(const char *str1,const char *str2){printf("%s,%s \n",str1,str2);return NULL;}const char *func2(FUNC1 p, const char *str1,const char *str2){return p(str1,str2);}int main() {ST student1;strcpy(student1.name,"奥巴马");student1.id = 1;printf("%d,%s \n",student1.id,student1.name);return 0;}chunli@ubuntu:~/pointer$ gcc -std=c99 main.c && ./a.out1,奥巴马
不使用typedef
使用typedef
本文出自 “李春利” 博客，请务必保留此出处http://990487026.blog.51cto.com/10133282/1782752