如何在创建的文本文件中保存我的 C++ 编译器输出？

Question

I am making a simple compiler using c++ but the output shows in my console window only!

class Scanner{
private:
    ifstream f;
    Token check_reserved(string s){
        if (s == "program") return PROGRAM_SY;
        else if (s == "is")return IS_SY;
        else if (s == "begin")return BEGIN_SY;
        else if (s == "end")return END_SY;
        else if (s == "var")return VAR_SY;
}

void display_tokens(void){
        Token t;
        if (f.eof())cout << "end_of_file " << endl;
        while (!f.eof()){
            t = get_token();
            switch (t){
            case PROGRAM_SY: cout << "program token" << endl; break;
            case IS_SY: cout << "is token" << endl; break;
            case BEGIN_SY: cout << "begin token" << endl; break;
            case END_SY: cout << "end token" << endl; break;
            }
        }

    }
};

int main(){

    ofstream myfile;
    myfile.open("example.txt");
    myfile << SC.display_tokens();
    myfile.close();

    string Filename;
    cout << "Enter Name of input File : ";
    cin >> Filename;
    Scanner SC(Filename);
    SC.display_tokens();
    SC.~Scanner();
}

I expected that my code will print my output in my console window in save it inside the text file. what is the problem here, and what is the right code to get my output?

Answer 1

One issue is that functions need to return values in order for you to output the value to a stream.

Your function declaration says that the function does not return a value:

void display_tokens(void)

Yet, you use the function as if it returns a value:

myfile << SC.display_tokens();

I recommend you review the subject of "functions" in your Compiler Theory book. Also, review "functions" in your favorite C++ book.

You could change the function:

void display_tokens(std::ostream& my_file)
{
    //...
    my_file << "Here are the tokens:\n";
    //...
}