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:
[cpp] view plain#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.\n")
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\n",buf)
fclose(stream)
system("pause")
return 0
}
DEMO2
[cpp] view plainint 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=0i<25i++)
{
list[i]=(char)('z'-i)
}
/*write 25 characters to stram*/
numwritten=fwrite(list,sizeof(char),25,stream)
printf("Wrote %d items\n",numwritten)
fclose(stream)
}
else
printf("Problem opening the file\n")
if ((stream=fopen("fread.out","r+t"))!=NULL)
{
numread=fread(list,sizeof(char),25,stream)
printf("Number of items read =%d\n",numread)
printf("Contents of buffer=%.25s\n",list)
fclose(stream)
}
else
{
printf("File could not be opened\n")
}
system("pause")
return 0
}
c语言中fread函数语法为size_t fread( void *restrict buffer, size_t size, size_t count, FILE *restrict stream )。buffer是指向要读取的数组中首个对象的指针,size是每个对象的大小(单位是字节),count是要读取的对象个数,stream是输入流。通过fread函数可进行数据读取,返回成功读取的对象个数。
扩展资料:
fread函数从给定输入流stream读取最多count个对象到数组buffer中(相当于以对每个对象调用size次fgetc),把buffer当作unsignedchar数组并顺序保存结果。流的文件位置指示器前进读取的字节数。
若出现错误,则流的文件位置指示器的位置不确定。若没有完整地读入最后一个元素,则其值不确定,可能小于count。若size或count为零,则fread返回零且不进行其他动作。fread不区分文件尾和错误,因此调用者必须用feof和ferror才能判断发生了什么。