What include
does is copying all the contents from the file (which is the argument inside the <>
or the ""
), so when the preproccesor finishes its work main.cpp
will look like:
// iostream stuff
int foo(int a){
return ++a;
}
int main(int argc, char *argv[])
{
int x=42;
std::cout << x <<std::endl;
std::cout << foo(x) << std::endl;
return 0;
}
So foo will be defined in main.cpp
, but a definition also exists in foop.cpp
, so the compiler “gets confused” because of the function duplication.