Question

c语言 write()、read()函数原型

Answer 1

把指定数量的数据写入文件，若成功则返回写入的字节数，否则返回-1
int _write( int handle, const void *buffer, unsigned int count );
这个例子中把字符串“hello”写入文件sample.txt中：
int Handle; char String[ ]="hello";
Handle = _open("sample.txt",_O_RDWR|_O_CREAT);
_write(Handle,String,sizeof(String));
_close(Handle);

从一个文件读取数据
int _read( int handle, void *buffer, unsigned int count );
这个例子中打开文件eof.c，每次读取10个字节，直到全部字节被读完为止，然后显示文件的长度：
void main( void ) {
int fh, count, total = 0;
char buf[10];
if( (fh = _open( "eof.c", _O_RDONLY )) == - 1 ) {
perror( "Open failed");
exit( 1 );
}
while( !_eof( fh ) ) {
if( (count = _read( fh, buf, 10 )) == -1 ) {
perror( "Read error" );
break;
}
total += count;
}
printf( "Number of bytes read = %d\n", total );
_close( fh );
}

Answer 2

read内部是调_read,_read的返回值在msdn中有这样的描述
_readreturnsthenumberofbytesread,whichmightbelessthancountiftherearefewerthancountbytesleftinthefileorifthefilewasopenedintextmode,inwhichcaseeachcarriagereturn–linefeed(cr-lf)pairisreplacedwithasinglelinefeedcharacter.onlythesinglelinefeedcharacteriscountedinthereturnvalue.thereplacementdoesnotaffectthefilepointer.
注意这一段:inwhichcaseeachcarriagereturn–linefeed(cr-lf)pairisreplacedwithasinglelinefeedcharacter
就是说如果用text模式打开的话,文件换行时可能在文本中有2个字符----换行和缩进(cr-lf),而在return的时候系统是把它作为1个回车符号('\n')所返回的.所以会导致这个情况

Answer 3

write: int write(int fd, char * buf, unsigned count);
read: int read(int fd, char * buf, unsigned count);