Character encoding issue for French characters in iOS

Question

I have some French text in my application. I need to write that text to the document directory as an HTML file. When I write the file using NSFileHandler, the strings with special characters are not saved correctly.

Here is my code :

NSString * udString =@"DÉTAIL DES ITEMS";
NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:htmFileName];
if (fileHandle){
    [fileHandle seekToEndOfFile];
    [fileHandle writeData:convertedlogoimageData];
    [fileHandle seekToEndOfFile];
    [fileHandle writeData:[udString dataUsingEncoding:NSUnicodeStringEncoding]];
    [fileHandle seekToEndOfFile];
}