g++ preprocessor output [closed]

Question

I want to get only preprocessed version of file.cc. I did g++ -E file.cc, got:

# 1 "file.cc"
# 1 "<command-line>"
# 1 "file.cc"

What did I do wrong?

Answer 1

Assumed that your source file contains a simple main function:

$ cat file.cc
int main() {
    return 0;
}

Then, with the command you showed, the output looks like this:

$ g++ -E file.cc
# 1 "file.cc"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "file.cc"

int main() {
    return 0;
}

The output which is shown in the question happens when file.cc is empty. Note that "empty" means that the file can still contain comments, or #ifdef blocks with a condition which evaluates to false - since the preprocessor filters them out, they do not appear in the output either.