Function to escape some characters for C++ string

问题

I need a function to escape some characters inside a std::string and so i made this:

static void escape(std::string& source,const  std::vector<std::string> & toEscape, const std::string& escape){
    //for each position of the string
    for(auto i = 0; i < source.size(); ++i){
        // for each substring to escape
        for(const auto & cur_to_escape : toEscape){
            // if the current position + the size of the current "to_escape" string are less than the string size and it's equal to the substring next of the i'th position
            if(i + cur_to_escape.size() < source.size() && source.substr(i, cur_to_escape.size()) == cur_to_escape){
                // then for each char of the current "to_escape", escape the current character with the "escape" string given as parameter
                /*
                 *  source = asd
                 *  toEscape = {"asd"}
                 *  escape = \
                 *  -> asd -> \asd -> \a\sd -> \a\s\d 
                 * */
                for(auto z = 0; z < cur_to_escape.size(); ++z){
                    source.insert(i, escape);
                    i+=escape.size();
                }
            }
        }
    }
}

and to test it i've used this:

int main() {
    std::string s = "need to escape \" , \\ and \n .";
    std::cout<<s;
    escape(s, {"\n", "\\", "\""}, "\\");
    std::cout<<"\n\n final string: "<<s;
}

and the output is

final string: need to escape \" , \\ and \
 .

and so the \n is not been escaped as intended... and i can't find the problem... any guesses?

回答1:

“and so the \n is not been escaped as intended” Yes, it is: the new-line character is there, as expected. If you expect an 'n' character, you are wrong. '\n' is a convention used to represent the "invisible" character New-Line (NL).

Here's a cleaner way to write the same thing (try it):

std::string escape(const char* src, const std::set<char> escapee, const char marker)
{
  std::string r;
  while (char c = *src++)
  {
    if (escapee.find(c) != escapee.end())
      r += marker;
    r += c; // to get the desired behavior, replace this line with: r += c == '\n' ? 'n' : c;
  }
  return r;
}
//...
std::string r = escape("\"this\" is a test\nthis is the second line", { '"', '\n' }, '\\');

回答2:

This is working code, but it is not optimal and can be made faster but probably also bigger.

void escape(std::string& source, const  std::vector<std::string>& to_escape, const std::string& escape) { 
    // for each substring to escape
    for (const auto &e : to_escape) {
        auto pos = source.find(e);
        while (pos != std::string::npos) {
            auto to_replace = escape+e;
            if (e=="\n") to_replace = escape+"n";
            else if (e=="\t") to_replace = escape+"t";
            source.replace(pos, e.size(), to_replace);
            const auto old_pos = pos;
            pos = source.find(e, old_pos + to_replace.size());
        }
    }
}

Live Code

来源：https://stackoverflow.com/questions/61035929/function-to-escape-some-characters-for-c-string

标签

c++

string

escaping