How to define a macro that take the file's name and read, write to same name but different extensions using freopen()

Im trying to create some #define in c++, but now im stuck in this part

   #include<bits/stdc++.h>
#define FASTRW ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define IO(filename) freopen(filename + ".inp", "r", stdin); freopen(filename + "out", "w", stdout)


using namespace std;

int main(){
    FASTRW;
    IO("lmao");
    return 0;
}

the first define worked just fine, but my vs code showed the error message: "expression must have integral or unscoped enum type" to the IO("lmao").

i tried to use chat GPT and it said that the previous code, which was the
#define IO(filename) freopen(filename + ".inp", "r", stdin); freopen(filename + "out", "w", stdout)"
should be
#define IO(filename) freopen((filename + ".inp").c_str(), "r", stdin); freopen((filename + ".out").c_str(), "w", stdout)
because the string need to be converted to the c string type using c_str().
i expected this code should be able to read, write in 2 same filenames but different extensions: the .inp and .out.
But when i pasted, the error remained the same, i also used Bard, but the result was the same as the chat GPT one. Restart the vs code, the problem was still there. the message just disappears if i remove the string expressions and use directly the "filename".

>Solution :

What you’re trying to do is concatenating strings, but there is no binary operator+ for char*.

You can either:

• Wrap the filename in a std::string and "unwrap" with a call to .c_str (not so sure about the lifetime issues that will come with this one)
• Limit the usability of your macro and restrict its input to string literals, in which case a single space will allow for concatenation (instead of a +)

For the first solution:

#define IO(filename) freopen((std::string{filename} + ".inp").c_str(), "r", stdin); freopen((std::string{filename} + "out").c_str(), "w", stdout)

For the second solution:

#define IO(filename) freopen(filename ".inp", "r", stdin); freopen(filename "out", "w", stdout)