CODEWITHSUNDEEP
c++
Pete
Pete

Reputation: 61

Making a function call to a function whose name is inside a string - C++

I am extracting a string from a .txt file and saving it in a variable:

std::string line = "The king's name is getKingName()";

Lets assume that getKingName() is a function that returns a King class' name data member.

How can I make a call to getKingName() when the string variable looks like that?

Upvotes: 0

Views: 156

Answers (3)

Shubham Patel
Shubham Patel

Reputation: 137

As far as I know, C++ does not provide such kind of functionality to interpolate functions call inside a string. All you can do implement your own logic to do that. Like,

1) define all the valid methods like this,

string getKingName(){
 return "Some name";
}

string otherMethods(){
  return "other values";
}

2) One helper method for mapping of function call

string whomToCall(string methodName){
    switch(methodName){
       case "getKingName()": 
          return getKingName();
          break;
       case "otherMethods()": 
          return otherMethods();
          break;
       default: 
          return "No such method exist";       
    }
}

3) break the line in tokens(words), read one by one and check for following condition also if token starts with any alphabetical character and ends with "()" substring

    istringstream ss(line);
    do { 
        string token; 
        ss >> token; 

        if(isMethod(token))
           cout << whomToCall(token) << " ";
         else
           cout << token<< " "; 
    } while (ss);

4) isMethod() to check if token's value can be a valid method name

bool isMethod(string token){
   int n= token.length();
   return isalpha(token[0]) && token[n-2]=='(' && token[n-1] == ')' ;
}

Upvotes: 2

Tiger4Hire
Tiger4Hire

Reputation: 1091

Amended

This answer is a little off subject. I will leave it up, because others might find it relevant, but I agree with other answers, a simple map->function will work better for your case.

This is not supported by C++. C++ is not an interpreted language. If you you want to do things like this, why not use an interpreted language, which do these sorts of things by default. Languages like lua are designed to call C/C++ functions with an interpreted language, with a small overhead.

However, if you really need to do this, it is possible, depending on your operating system. For example,

  1. On windows start with dbghelp. You will need to build a pdb, (e.g. build with symbols).
  2. On linux, you will also need to build symbols (-g), and use something like dlsym see here for a discussion.

That said, there are lots of gotchas doing it this way. Optimization can get in the way (best to disable them). Also best to avoid dynamic linking (prefer static). You will also need to cope with C++ name mangling (the name of the function is not the name of your function in C++). see https://blog.oakbits.com/how-to-mangle-and-demangle-a-c-method-name.html.

Upvotes: 0

RoQuOTriX
RoQuOTriX

Reputation: 3001

This would be the easiest solution, but I think your problem consists of several such calls?

std::string line = "The king's name is getKingName()";
if (line.find("getKingName()") != std::string::npos) {  
    King name = getKingName();
}

Upvotes: 1

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