C語言庫函數名:
簡介
函數原型：
size_t fread(void *buffer, size_t size, size_tcount, FILE *stream);
功 能：
從一個文件流中讀數據,讀取count個元素,每個元素size字節.如果調用成功返回count.如果調用成功則實際讀取size*count字節
參 數：
buffer
用於接收數據的內存地址,大小至少是size*count 字節.
size
單個元素的大小，單位是字節
count
元素的個數,每個元素是size字節.
stream
輸入流
返回值：
實際讀取的元素數.如果返回值與count(不是count*size)不相同,則可能文件結尾或發生錯誤.
從ferror和feof獲取錯誤信息或檢測是否到達文件結尾.
程序例
#include <stdio.h>
#include <string.h>
int main(void)
{
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);
return 0;
}
MSDN示例
#include <stdio.h>
void 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 stream */
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 )
{ /* Attempt to read in 25 characters */
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" );
}
