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c语言fread函数的用法

时间: 长思709 分享

c语言fread函数的用法

  C语言中:fread是一个函数。从一个文件流中读数据,最多读取count个元素,每个元素size字节,如果调用成功返回实际读取到的元素个数,如果不成功或读到文件末尾返回 0。下面我们来看看c语言fread函数的用法。

  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=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;

  }

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