escape forward slash by backslash using regular expressions of C++11

I need to match a string of any characters escaping forward slashes by backslash.

Some examples (in c++ string you need twice more backslashes then in the exmaples):

sdfsdfkjl/sdf  // does not match
sdfsdfkj\/sdf  // does match
sdfsdfk\\/sdf  // does not match
sdfsdf\\\/sdf  // does match
sdfsdfk\\/sd\\\/f  // does not match
sdfsdf\\\/sdf\\\/f  // does match
// and so on

I suppose there should be something like this

std::regex const regEx(
  "((?:(?:(?!\\\\)\\\\/)|(?:(?:\\\\\\\\)+\\\\/)|(?:[^/]))*)");

But it does not work for some reasons. My guess is that it is related to lookahead operation.