How to control txt file reading

I have the following entry in a file .txt :

var a;
var b; var c;
a = (10+2)/2;
b = a*2;
c = a*b;
print a; print b; print c;

Where the getToken () function will return me the current token, containing the type and its value. For example:

1st method call getToken() : will return an object of type Token , containing keywordChave and var

2nd method call getToken() : will return an object of type Token , containing ID and a

3rd call of method getToken() : will return an object of type Token , containing delimiter and ;

and so on.

In other words, I need to analyze the file in such a way that it is possible to control where I got the last token . The code below is impractical because I can not control which part of the file I captured the last symbol:

if(entrada.is_open()){
    while(getline(entrada, linha)){
        int tam_linha = linha.size();
        for(int i=0; i<=tam_linha-1; i++){
        }
    }
}

So, how do I get the file to be read "interrupt" by calling the getToken() function and return the next symbol?

Appendix: