关于Fwrite（）的问题

这是VFP帮助里的例子，加了一行“FWRITE(gnFileHandle, "abcd" )”，希望将字符串“abcd”写入文件，却没有成功，问题出在哪？
Local gnFileHandle,nSize,cString
gnFileHandle = FOPEN("D:\kejian\file_s\sd.txt")
* Seek to end of file to determine number of bytes in the file.
nSize =  FSEEK(gnFileHandle, 0, 2)     && 移动指针到末尾
IF nSize <= 0
 * If file is empty, display an error message.
 WAIT WINDOW "This file is empty!" NOWAIT
ELSE
 * If file is not empty, store the file's contents in memory
 * and display the text in the main Visual FoxPro window.
 = FSEEK(gnFileHandle, 0, 0)      && 移动指针到开始
 cString = FREAD(gnFileHandle, nSize)
  =FWRITE(gnFileHandle, "abcd" )
ENDIF
= FCLOSE(gnFileHandle)         && 关闭文件

[此贴子已经被作者于2021-4-28 20:24编辑过]