c語言fread函式的用法
C語言中：fread是一個函式。從一個檔案流中讀資料，最多讀取count個元素，每個元素size位元組，如果呼叫成功返回實際讀取到的元素個數，如果不成功或讀到檔案末尾返回 0。下面我們來看看c語言fread函式的用法。
fread()函式---- Reads data from a stream.
#include<stdio.h>
size_t fread( void *buffer, size_t size, size_t count,FILE *stream );
從一個檔案流中讀資料,讀取count個元素,每個元素size位元組.如果呼叫成功返回count.如果呼叫成功則實際讀取size*count位元組
buffer的大小至少是 size*count 位元組.
return:
fread returns the number of full items actually read
實際讀取的元素數.如果返回值與count(不是count*size)不相同,則可能檔案結尾或發生錯誤.
從ferror和feof獲取錯誤資訊或檢測是否到達檔案結尾.
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("","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("%sn",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("","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 itemsn",numwritten);
fclose(stream);
}
else
printf("Problem opening the filen");
if ((stream=fopen("","r+t"))!=NULL)
{
numread=fread(list,sizeof(char),25,stream);
printf("Number of items read =%dn",numread);
printf("Contents of buffer=%.25sn",list);
fclose(stream);
}
else
{
printf("File could not be openedn");
}
system("pause");
return 0;
}
