对文本内容进行增，删，改，保存

再写另一个类似的题目时，发现这个代码错误很多，做更改如下，希望各位大佬指正：

 

首先需要明确的一点：当结构作为函数参数被传递时，用指针作为参数，特点是可以修改原结构数据；传递结构，则有利于保护原始数据。

不然，就看各种烫烫烫，或者各种乱码，看得人抓狂。

以及对指向结构的指针，记得要初始化。

 

1.删除部分

/*传递了结构，但是下面声明了一个指针指向结构的指针,再将变更后的结构赋给指针*/

void del(struct book library[])    
{
    extern int count;
    struct book* pt;             
    pt = &library[0];

    int del;
    int i = 0, j = 0;

    puts("Which content would you like to delete?Press q to the menu:");
    for (int index = 0; index < count; index++,pt++)
        printf("%s by %s : %.2f.\n", pt->title, pt->author, pt->value);
    while (scanf("%d", &del) == 1)
    {
        while (i < count)
        {
            if (j == (del - 1))                 //加入需要删除第一条目录，在结构数组中该目录其实是第0条，所以减去1
            {                                   
                j++;
                continue;
            }
            else
            {
                library[i] = library[j] ;       //变更结构内容，此时的结构为原结构副本，并不会影响原始数据
                pt[i] = library[i];             
                i++;
                j++;
            }
        }
        count = count - 1;                      //我将count声明为一个外部变量，方便全局调用。
        puts("Which content would you like to delete?Press q to the menu:");
    }
    puts("What is you next moving:");
    while (getchar() != '\n')                    //这个将缓存中换行符读取掉的语句真的不知道写了多少遍....
        continue;

}

2.保存

    if (count > 0)            //保存
    { 
        extern int count;
        puts("Here is the list of your book:");
        for (index = 0; index < count; index++)
            printf("%s by %s : %.2f.\n", library[index].title, library[index].author, library[index].value);
        pbooks = fopen("book.dat", "w+b");             //在另一个相似程序中，复制了这段，忘记改文件名，崩溃了一天.....
        fwrite(&library[0], size, count, pbooks)；     //由于会删去某个结构，所以选择了”W+b“模式，打开文件清楚所有内容，再重新写入
    }                                                 //可以增添个判断，即如果没有删过内容，那么就可以用”a+b"，在接着以前的内容继续写入
                                                     //fwrite(&library[filecount],size,count-filecount,pbooks);
    else
        puts("No books.");
    fclose(pbooks);
 

3.更改结构的数据，利用指向结构的指针。

本来使用switch来对更改部分做选择，但是考虑到case中的break,会直接跳出循环，所以用了else if,如果修改完后，发现还需要继续修改，可以直接选择需要修改的部分。

void change(struct book * ptr)
{
    char ch;
    struct book temp;
    
    int i = 0;

    puts("Which item do you want to change,press Q to jump to the menu?");
    while (scanf("%d", &i) == 1)
    {
        temp = ptr[i - 1];
        while (getchar() != '\n')
            continue;

        puts("Which part do you want to change?");
        puts("a. Title     b.Author     c.Value   d.ignore  ");
        while ((ch = getchar()) == 'a' || ch == 'b' || ch == 'c')
        {
            while (getchar() != '\n')
                continue;

            if (ch == 'a')
            {
                puts("Enter the new title:");
                s_gets(temp.title, MAXTITL);
            }
            else if (ch == 'b')
            {
                puts("Enter the new author:");
                s_gets(temp.author, MAXTITL);
            }
            else if (ch == 'c')
            {
                puts("Enter the new value:");
                scanf("%f", &temp.value);
                while (getchar() != '\n')
                    continue;
            }
            else
                break;
            ptr[i - 1] = temp;

            puts("Need to change this item again,y/n?");
            if ((ch = getchar()) == 'y')
            {
                puts("Which part do you want to change?");
                puts("a. Title     b.Author     c.Value   d.ignore ");
                while (getchar() != '\n')
                    continue;
            }
            else
                break;
        }
        puts("Which item do you want to change (press Q to jump to the menu):");    
    }    
    while (getchar() != '\n')
        continue;
}

4，新增内容，同样传递指针

void add(struct book * pt)
{
    struct book temp;
    temp = *pt;
    puts("Please add new book title:");
    puts("Please press [Enter] at the start of a line to stop.");
    while (count < MAXBKS && s_gets(temp.title, MAXTITL) != NULL && temp.title[0] != '\0')
    {    
        puts("Enter the author:");
        s_gets(temp.author, MAXAUTL);
        puts("Enter the value:");
        scanf("%f", &temp.value);
        pt[count] = temp;
        count++;
        while (getchar() != '\n')
            continue;
        if (count < MAXBKS)
            puts("Keeping add new book title ,press [Enter] at the start of a line to menu . ");
    }
}

 

完整代码如下：

# include <stdio.h>
# include <stdlib.h>
# include <string.h>

# define MAXTITL 30
# define MAXAUTL 30
# define MAXBKS  10

char* s_gets(char* st, int n);

struct book {
    char title[MAXTITL];
    char author[MAXAUTL];
    float value;
};

int count = 0;

void menu(struct book library[]);
void add(struct book library[]);
void del(struct book library[]);
void change(struct book*);
int main()
{
    struct book library[MAXBKS];
    extern int count;
    int index, filecount;
    FILE* pbooks;
    int size = sizeof(struct book);

    if ((pbooks = fopen("book.dat", "r+b")) == NULL)   //二进制模式读写文件，并在文件末尾更新
    {
        fputs("Can't open book.dat file\n", stderr);
        exit(EXIT_FAILURE);
    }

    rewind(pbooks);

    while (count < MAXBKS && fread(&library[count], size, 1, pbooks) == 1)
    {
        if (count == 0)
            puts("Current contents of book.dat:");
        printf("%s by %s :%.2f\n", library[count].title, library[count].author, library[count].value);
        count++;
    }
    filecount = count;

    if (count == MAXBKS)
    {
        fputs("The book.dat is full.", stderr);
        exit(2);
    }

    menu(library);


    if (count > 0)            //保存
    {
        extern int count;
        puts("Here is the list of your book:");
        for (index = 0; index < count; index++)
            printf("%s by %s : %.2f.\n", library[index].title, library[index].author, library[index].value);
        pbooks = fopen("book.dat", "w+b");
        fwrite(&library[0], size, count, pbooks);
    }
    else
    {
        puts("No books.");
    }

    puts("Bye.");
    fclose(pbooks);

    return 0;
}

void menu(struct book library[])
{
    struct book* ptr = &library[0];
    char c;
    puts("Please select your moving:");
    puts("a. adding new book         b.  delete content");
    puts("c. change the content      d.  quit, saving change");
    while ((strchr("abcd",c = getchar()) != NULL))
    {
        while (getchar() != '\n')
            continue;
        switch(c)
        {
        case 'a': add(library); break;
        case 'b': del(library);        break;
        case 'c': change(ptr); break;           
        }
        if (c == 'd')
            break;
        puts("a. adding new book         b.  delete content");
        puts("c. change the content      d.  quit, saving change");
    }
}

void add(struct book * pt)           //增加新的内容
{
    struct book temp;
    temp = *pt;
    puts("Please add new book title:");
    puts("Please press [Enter] at the start of a line to stop.");
    while (count < MAXBKS && s_gets(temp.title, MAXTITL) != NULL && temp.title[0] != '\0')
    {    
        puts("Enter the author:");
        s_gets(temp.author, MAXAUTL);
        puts("Enter the value:");
        scanf("%f", &temp.value);
        pt[count] = temp;
        count++;
        while (getchar() != '\n')
            continue;
        if (count < MAXBKS)
            puts("Keeping add new book title ,press [Enter] at the start of a line to menu . ");
    }
}
void del(struct book library[])
{

    struct book* pt;
    pt = &library[0];

    int del;
    int i = 0, j = 0;

    puts("Which content would you like to delete?Press q to the menu:");
    for (int index = 0; index < count; index++,pt++)
        printf("%s by %s : %.2f.\n", pt->title, pt->author, pt->value);
    while (scanf("%d", &del) == 1)
    {
        while (i < count)
        {
            if (j == (del - 1))
            {
                j++;
                continue;
            }
            else
            {
                library[i] = library[j] ;
                pt[i] = library[i];
                i++;
                j++;
            }
        }
        count = count - 1;
        puts("Which content would you like to delete?Press q to the menu:");
    }
    puts("What is you next moving:");
    while (getchar() != '\n')
        continue;

}

void change(struct book * ptr)
{
    char ch;
    struct book temp;
    
    int i = 0;

    puts("Which item do you want to change,press Q to jump to the menu?");
    while (scanf("%d", &i) == 1)
    {
        temp = ptr[i - 1];
        while (getchar() != '\n')
            continue;

        puts("Which part do you want to change?");
        puts("a. Title     b.Author     c.Value   d.ignore  ");
        while ((ch = getchar()) == 'a' || ch == 'b' || ch == 'c')
        {
            while (getchar() != '\n')
                continue;

            if (ch == 'a')
            {
                puts("Enter the new title:");
                s_gets(temp.title, MAXTITL);
            }
            else if (ch == 'b')
            {
                puts("Enter the new author:");
                s_gets(temp.author, MAXTITL);
            }
            else if (ch == 'c')
            {
                puts("Enter the new value:");
                scanf("%f", &temp.value);
                while (getchar() != '\n')
                    continue;
            }
            else
                break;
            ptr[i - 1] = temp;

            puts("Need to change this item again,y/n?");
            if ((ch = getchar()) == 'y')
            {
                puts("Which part do you want to change?");
                puts("a. Title     b.Author     c.Value   d.ignore ");
                while (getchar() != '\n')
                    continue;
            }
            else
                break;
        }
        puts("Which item do you want to change (press Q to jump to the menu):");    
    }    
    while (getchar() != '\n')
        continue;
}

char* s_gets(char* st, int n)
{
    char* ret_val;
    char* find;

    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        find = strchr(st, '\n');
        if (find)
            *find = '\0';
        else
            while (getchar() != '\n')
                continue;
    }

    return ret_val;
}