C语言fread函数了解

fread()函数---- Reads data from a stream.

#include<stdio.h>

size_t fread( void *buffer, size_t size, size_t count,FILE *stream );

从一个文件流中读数据,读取count个元素,每个元素size字节.如果调用成功返回count.如果调用成功则实际读取size*count字节

buffer的大小至少是 size*count 字节.

return:

fread returns the number of full items actually read

实际读取的元素数.如果返回值与count(不是count*size)不相同,则可能文件结尾或发生错误.

从ferror和feof获取错误信息或检测是否到达文件结尾.

DEMO:

#include <stdio.h>
#include <process.h>
#include <string.h>
int main()
{
	FILE *stream;
	char msg[]="this is a test";
	char buf[20];
	if ((stream=fopen("dummy.fil","w+"))==NULL)
	{
		fprintf(stderr,"cannot open output file.
");
		return 1;
	}
	/*write some data to the file*/
	fwrite(msg,1,strlen(msg)+1,stream);
	/*seek to the beginning of the file*/
	fseek(stream,0,SEEK_SET);
	/*read the data and display it*/
	fread(buf,1,strlen(msg)+1,stream);
	printf("%s
",buf);
	fclose(stream);
	system("pause");
	return 0;
}

DEMO2

int main(void)
{
	FILE *stream;
	char list[30];
	int i,numread,numwritten;
	/*open file in text mode:*/
	if ((stream=fopen("fread.out","w+t"))!=NULL)
	{
		for (i=0;i<25;i++)
		{
			list[i]=(char)("z"-i);
		}
		/*write 25 characters to stram*/
		numwritten=fwrite(list,sizeof(char),25,stream);
		printf("Wrote %d items
",numwritten);
		fclose(stream);
	}
	else
		printf("Problem opening the file
");
        if ((stream=fopen("fread.out","r+t"))!=NULL)
        {
			numread=fread(list,sizeof(char),25,stream);
			printf("Number of items read =%d
",numread);
			printf("Contents of buffer=%.25s
",list);
			fclose(stream);
        } 
        else
        {
			printf("File could not be opened
");
        }
	system("pause");
	return 0;
}

【FROM MSDN &&百科】