Hello, @张锋, and All,
Probably, your text contains NO character with Unicode value over \x{007F} ;-))
Remember that, when the Unicode value of a character is :
Under \x{0080}, the N++ ANSI and UTF-8 encodings are strictly equivalent and use 1 byte to encode the character
Over \x{007F}, the UTF-8 and UTF-8 BOM encodings use from 2 to 4 bytes, whereas the ANSI encoding still use a 1 byte to encode that character !
So, if your text contains only pure ASCII characters ( under \x{0080} ), there no way, for Notepad++, on opening that file, to determine the right encoding, and it chooses, by default, the UTF-8 encoding, ( which does not contain the invisible BOM : Byte Order Mark )
So, to be sure that the ANSI encoding will be kept, just change this default behavior :
Choose the Settings > Preferences > New document option
In the Encoding section, just uncheck the squared box Apply to opened ANSI files
Close the Preferences dialog , by clicking on the Close button
Preferably, stop and re-start Notepad++
Best Regards,
guy038