Outputting to a file question

I have the piece of code:

outfile.open (filename.c_str());

where filename is the filename.txt provided by the user.

However, how would I add .csv to end of that so I can change the file extension and create a new file?

so basically the outfile name would look like this

filename.txt.csv

-jeff

There are quite a few ways of doing this.
Assuming that filename contains expected data, this is one option:

Code:

---

outfile.open(std::string(filename + ".csv").c_str());

---

Code:

---

        string str;
        str = "hello";
        str += " world";
        cout<<str<<endl;  //hello world

---