Allow user to pass a separator character by doubling it in C++

Question

I have a C++ function that accepts strings in below format:

<WORD>: [VALUE]; <ANOTHER WORD>: [VALUE]; ...

This is the function:

std::wstring ExtractSubStringFromString(const std::wstring String, const std::wstring SubString) {

    std::wstring S = std::wstring(String), SS = std::wstring(SubString), NS;
    size_t ColonCount = NULL, SeparatorCount = NULL; WCHAR Separator = L';';

    ColonCount = std::count(S.begin(), S.end(), L':');
    SeparatorCount = std::count(S.begin(), S.end(), Separator);

    if ((SS.find(Separator) != std::wstring::npos) || (SeparatorCount > ColonCount))
    {
        // SEPARATOR NEED TO BE ESCAPED, BUT DON'T KNOW TO DO THIS.
    }

    if (S.find(SS) != std::wstring::npos)
    {
        NS = S.substr(S.find(SS) + SS.length() + 1);

        if (NS.find(Separator) != std::wstring::npos) { NS = NS.substr(NULL, NS.find(Separator)); }
        if (NS[NS.length() - 1] == L']') { NS.pop_back(); }

        return NS;
    }
    return L"";
}

Above function correctly outputs MANGO if I use it like:

ExtractSubStringFromString(L"[VALUE: MANGO; DATA: NOTHING]", L"VALUE")

However, if I have two escape separators in following string, I tried doubling like ;;, but I am still getting MANGO instead ;MANGO;:

ExtractSubStringFromString(L"[VALUE: ;;MANGO;;; DATA: NOTHING]", L"VALUE")

Here, value assigner is colon and separator is semicolon. I want to allow users to pass colons and semicolons to my function by doubling extra ones. Just like we escape double quotes, single quotes and many others in many scripting languages and programming languages, also in parameters in many commands of programs.

I thought hard but couldn't even think a way to do it. Can anyone please help me on this situation?

Thanks in advance.

Answer 1

You should search in the string for ;; and replace it with either a temporary filler char or string which can later be referenced and replaced with the value.

So basically:

1) Search through the string and replace all instances of ;; with \tempFill
- It would be best to pick a combination of characters that would be highly unlikely to be in the original string.
2) Parse the string
3) Replace all instances of \tempFill with ;

Note: It would be wise to run an assert on your string to ensure that your \tempFill (or whatever you choose as the filler) is not in the original string to prevent an bug/fault/error. You could use a character such as a \n and make sure there are non in the original string.

Disclaimer: I can almost guarantee there are cleaner and more efficient ways to do this but this is the simplest way to do it.