how to include text file as string at compile time without adding c++11 string literal prefix and suffix in the text file

I'm aware of many similar questions on this site. I really like the solution mention in the following link:

https://stackoverflow.com/a/25021520/884553

with some modification, you can include text file at compile time, for example:

constexpr const char* s = 
#include "file.txt"

BUT to make this work you have to add string literal prefix and suffix to your original file, for example

R"(
This is the original content,
and I don't want this file to be modified. but i
 don't know how to do it.
)";

My question is: is there a way to make this work but not modifying file.txt?

(I know I can use command line tools to make a copy, prepend and append to the copy, remove the copy after compile. I'm looking for a more elegant solution than this. hopefully no need of other tools)