了解

这两个函数是以二进制形式处理数据中，不同于其他I/O函数，是以文本形式处理。

函数

fread()

  • 作用：将文件中的内容拷贝到数组中

  1. 参数：
    (地址，数据块，数据块个数，文件指针)

  2. 返回值：
    两种情况：1.返回文件中成功读取项的数量。2.遇到文件结尾返回0

fwrite()

  • 作用：将n个数据块拷贝到文件中
  1. 参数
    (地址，数据块，数据块的个数，文件指针)

示例

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#include<stdio.h>
#include<stdlib.h>
#define SIZE 256
int main(int argc, char *argv[])
{
    FILE *in, *out;
    int bytes;
    char temp[SIZE];

    if (argc != 3)
    {
        fprintf(stderr, "Usage: %s filename\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    if ((in = fopen(argv[1], "r")) == NULL)
    {
        fprintf(stderr, "I couldn't open the file \"%s\"\n", argv[1]);
        exit(EXIT_FAILURE);
    }
    if ((out = fopen(argv[2], "w")) == NULL)
    {
        fprintf(stderr, "I couldn't open the file \"%s\"\n", argv[2]);
        exit(EXIT_FAILURE);
    }
    //把argv[1]文件中的256个以下的字符，copy到数组temp中，到文件结尾返回0
    while ((bytes = fread(temp, sizeof(char), 256, in)) > 0)
    {//把数组中的字符copy到argv[2]文件
        fwrite(temp, sizeof(char), bytes, out);
    }
    fclose(in);
    fclose(out);
    return 0;
}
将结构保存到文件
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#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS 10
char * s_gets(char * st, int n);
struct book 
{
	char title[MAXTITL];
	char author[MAXAUTL];
	float value;
};

int main()
{
	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)//在文件末尾写入，且以二进制打开
	{
		fputs("Can't open book.dat file\n", stderr);
		exit(1);
	}
	rewind(pbooks);//定位到文件开始，准备读取已有的内容
	while (count < MAXBKS && fread(&library[count], size, 1, pbooks) == 1)//判断能否读取1项
	{
		if(count == 0)
			puts("Curren 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 file is full.", stderr);
		exit(2);
	}
	//开始从键盘上读入数据
	puts("Plese add new book titles.");
	puts("Press [enter] at the start 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);
		while (getchar() != '\n')
			continue;		//清空输入行
		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');
		if (find)
			*find = '\0';
		else
			while (getchar() != '\n')
			continue;
	}
	return ret_val;
}