C基础-结构体-8-把结构内容保存到文件中

谁借莪１个温暖的怀抱￠ 2022-12-15 11:07 159阅读 0赞

/*
    把结构内容保存到文件中。
    由于结构可以储存不同类型的信息，所以它是构建数据库的重要工具。
    例如，可以用一个结构储存雇员或汽车零件的相关信息。最终，我们要把这些信息储存在文件中，并且能再次检索。
    数据库文件可以包含任意数量的此类数据对象。
    储存在一个结构中的整套信息被称为记录（record），单独的项被称为字段（field）。
    */
    
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    #define MAXTITL 40
    #define MAXAUTL 40
    #define MAXBKS  2
    
    char * s_gets(char * st, int n);
    
    struct book
    {
    	 char title[MAXTITL];
    	 char author[MAXAUTL];
    	 float value;
    };
    
    int main(void)
    {
    	struct book library[MAXBKS];
    	int count = 0;
    	int index, filecount;
    	FILE *pbooks;
    	int size=sizeof(struct book);
    	
    	if ((pbooks = fopen("book.dat","a+b")) ==NULL)
    	{
    		fputs("Can't open book.dat file\n",stderr);
    		exit(1);
    	}
    	 
    	rewind(pbooks); /* 定位到文件开始 */
    	
    	
    	/*
    	从文件里读取所有结构体信息
    	*/
    	while (count < MAXBKS && fread(&library[count],size,1,pbooks) == 1)
    	{
    		if(0 == count)
    		{
    			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(MAXBKS == count)
    	{
    		fputs("the book.dat file is full.\n",stderr);
    	    exit(2);
    	}
    
    	/*
    	先从输入端获取数据给结构体，再将结构体数据写到文件内。
    	*/
    	puts("please add new book title.");
    	puts("press [enter] at the strat of a line to stop.");
    	while(count < MAXBKS && s_gets(library[count].title,MAXTITL) != NULL && library[count].title[0] != '\0')
    	{
    		puts("now enter the author.");
    		s_gets(library[count].author, MAXAUTL);
    		puts("now enter the value.");
    		scanf("%f", &library[count].value);
    		count++;
    		while(getchar() != '\n')
    			continue;
    		if(count < MAXBKS)
    			puts("Enter the next title.");
    		
    	}
    	
    	if(count > 0)
    	{
    		puts("Here is the list of your books:");
    		
    		for(index=0;index<count;index++)
    		{
    			printf("%s by %s: $%.2f\n", library[index].title,library[index].author,library[index].value);
    		}
    		
    		fwrite(&library[filecount],size,count-filecount,pbooks);
    	}
    	else
    	{
    		puts("NO books? Too bad.\n");
    	}
    	
    	puts("bye.\n");
    	fclose(pbooks);
    	
    	return 0;
    }
    
    
    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'); //查找换行符
    		if(find)
    		{
    			*find='\0';  //在此处放置一个空字符
    		}
    		else
    		{
    			while(getchar() != '\n')
    				continue; //清理输入行
    		}
    		
    	}
    	
    	return ret_val;
    }

执行结果：
    
    please add new book title.
    press [enter] at the strat of a line to stop.
    
    NO books? Too bad.
    
    bye.
    
    //=========================================================================
    
    please add new book title.
    press [enter] at the strat of a line to stop.
    book1
    now enter the author.
    author1
    now enter the value.
    1
    Enter the next title.
    
    Here is the list of your books:
    book1 by author1: $1.00
    bye.
    //=========================================================================
    
    Current contents of book.dat :
    book1 by author1: $1.00
    please add new book title.
    press [enter] at the strat of a line to stop.
    book2
    now enter the author.
    author2
    now enter the value.
    2
    Here is the list of your books:
    book1 by author1: $1.00
    book2 by author2: $2.00
    bye.
    
    //=========================================================================
    Current contents of book.dat :
    book1 by author1: $1.00
    book2 by author2: $2.00
    the book.dat file is full.