c語言fread函數(shù)的用法
c語言fread函數(shù)的用法
C語言中：fread是一個函數(shù)。從一個文件流中讀數(shù)據(jù)，最多讀取count個元素，每個元素size字節(jié)，如果調(diào)用成功返回實(shí)際讀取到的元素個數(shù)，如果不成功或讀到文件末尾返回 0。下面我們來看看c語言fread函數(shù)的用法。
fread()函數(shù)---- Reads data from a stream.
#include<stdio.h>
size_t fread( void *buffer, size_t size, size_t count,FILE *stream );
從一個文件流中讀數(shù)據(jù),讀取count個元素,每個元素size字節(jié).如果調(diào)用成功返回count.如果調(diào)用成功則實(shí)際讀取size*count字節(jié)
buffer的大小至少是 size*count 字節(jié).
return:
fread returns the number of full items actually read
實(shí)際讀取的元素?cái)?shù).如果返回值與count(不是count*size)不相同,則可能文件結(jié)尾或發(fā)生錯誤.
從ferror和feof獲取錯誤信息或檢測是否到達(dá)文件結(jié)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=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\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;
}