C语言结构体、链表、指针

先吐槽一下、学iOS的比Android苦逼的多了、面试的时候问C、C++、数据结构、算法等等等、就算你实战经验很强、如果你这些不懂的话还是不行的。人Android面试的问Java就可以了。。。

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• 每次都会忘了结构体、指针这些玩意、所以现在把这些东西都整理一下

#import <Foundation/Foundation.h>
#include "test.h"
#include <string.h>
struct Books {
    char title[50];
    char author[50];
    char subject[100];
    int book_id;
};

struct BS{
    unsigned a:1;
    unsigned b:2;
    unsigned c:3;
}bit, *pbit;

void printBook(struct Books *book);
int main(int argc, const char * argv[]) {
    @autoreleasepool {

        int a =10;
        char *p;
        struct Books book1,book2; //结构体
        struct Books *book3;  //结构体指针
        book3 = &book1;

        strcpy(book1.title, "book1");
        strcpy(book2.title, "book2");
        printf("book1 title=%s\nbook2 title=%s\n", book1.title,book2.title);
        printf("book3 title=%s\n", book3->title);
        printf("book1=%p\n",&book1);
        printBook(&book1);

        printf("a in stack at:%p\n", &a);
        p = (char *)malloc(sizeof(char));        //基础类型malloc
        if (p)
            printf("Memory Allocated at: %p\n", p);
        else
            printf("Not Enough Memory!\n");

        free(p);

        bit.a = 1;
        bit.b = 3;
        bit.c = 7;
        printf("%d,%d,%d\n",bit.a,bit.b,bit.c);
//        struct BS bit1;
        struct BS *bit1 = (struct BS *)malloc(sizeof(struct BS *)); //结构体malloc

        pbit = bit1;
//        pbit = &bit;
//        (*pbit).a equal bit.a
        pbit->a = 0;  //结构体指针 使用成员变量要使用->
        pbit->b &= 2;
        pbit->c |= 5;
        printf("%d,%d,%d\n",pbit->a,pbit->b,pbit->c);
        printf("%d,%d,%d\n",bit.a,bit.b,bit.c);

    }
    return 0;
}

void printBook(struct Books *book)
{
    printf("book title:%s\n", book->title);
    printf("book author:%s\n", book->author);
    printf("book subject:%s\n", book->subject);
    printf("book book_id:%d\n", book->book_id);
}

C语言双向链表、二级指针解析

1、先抛出一个C语言的题目：
下面这段程序能否正确实现指针str开辟num空间

 #include "stdafx.h"
 #include <iostream>
 using namespace std;
 void GetMemory(char *p, int num)
 {
    p = (char *)malloc(sizeof(char) * num);
 //p = new char[num];  //C++当中
 }
 int _tmain(int argc, _TCHAR* argv[])
 {
    char *str = NULL;
    GetMeory(str, 100);
    strcpy(str,"Hello");
    cout << str << endl;
    return 0;
 }

答案是：程序会崩溃、不能开辟空间、 实参与形参
分析:str是一个指针、 指向NULL 形参p也是一个指针， 初始malloc 也指向NULL,虽然方法里面形参的指向改变了 但是实参str 仍然指向NULL

2、双向链表如下

1、初始化链表

typedef struct Node pNode;
struct Node {
    int data;
    pNode *prev, *next;
};

pNode *InitList(pNode **head, int n)
{
    pNode *p, *s;
    (*head) = (pNode *)malloc(sizeof(pNode));
    if ((*head)==NULL) exit(0);

    (*head)->next = NULL;
    (*head)->prev = NULL;

    p = (*head);
    int i;
    for (i = 0; i<n; ++i) {
        s = (pNode *)malloc(sizeof(pNode));
        if (s == NULL) exit(0);
        printf("Input the value of the %dth node:", i + 1);
        scanf("%d", &s->data);
        s->next = NULL;
        p->next = s;
        s->prev = p;
        p = s;
    }
    return p;
}

2、遍历打印

void PrintList(pNode *head)
{
    pNode *p;
    p = head->next;
    if (head->next == NULL) printf("the list is empty\n");
    while (p != NULL) {
        printf("%d ", p->data);
        p = p->next;
    }
    printf("\n");
}

3、清空链表

 pNode *p;
    while ((*head)->next != NULL) {
        p = (*head);
        p->next->prev = NULL;  // p next->prev 为NULL
        (*head) = p->next;
        free(p);
    }

4、删除链表中某一个元素

void DeleNumList(pNode **head, int n)
{
    int i;
    pNode *p;
    p = (*head)->next;
    for (i = 1; i<n; ++i) p = p->next;

    if (p->next == NULL) {
        p->prev->next = NULL;
        free(p);
    }else{
        p->next->prev = p->prev;
        p->prev->next = p->next;
        free(p);
    }

}

5、main函数

    pNode *head, *last;
    /***************************************************************/
    printf("Please input the size of the list:");
    scanf("%d", &n);
    last = InitList(&head, n);
    printf("%d %d \n",head->next->data, last->data);
    PrintList(head);