CMake: how to get the backslash literal in Regexp replace?

Question

I am trying to replace forwardslashes with backslashes. To do that i have the following line of code:

STRING(REGEX REPLACE "/" "\\" SourceGroup ${SourceGroupPath} )

SourceGroupPath = A/File/Path. SourceGroup is the variable to set the result to.

The problem i am having is with, the "\\" part to the code. I have tried several ways to getting to use the backslash literal like "\\" and using unicode but nothing seems to work.

The error i get in CMake is:

CMake Error at CMakeLists.txt:41 (STRING): string sub-command REGEX, mode REPLACE: replace-expression ends in a backslash.

Can someone please help me out?

Thanks,

Wouter

Answer 1

The reason is that in a CMake string literal, the backslash is an escape character (just like in C, Java or JavaScript) and in regex, the backslash is an escape character as well.

So to represent a regex as a string literal, you need double escaping. (That's why many "higher level" languages have regex literal notation, BTW.)

The string literal "\\" represents the in-memory string "\" and that's an invalid regex, hence the "ends in a backslash" error.

The string literal "\\\\" represents "\\" in memory which is a valid regex (representing a single backslash).