Dont modify program, print some values as output - unusual (?) homework [closed] - c++

Question

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Closed 10 years ago.
I have a problem with, to me, unusual homework:
Dont modify the main function but change the program that it prints as
output:
Monday
is the first day
of the week
And heres the given code:
int main()
{
cout << "is the first day\n";
}
Any help will be appreciated :)

Answer 1

What he's undoubtedly interested in your demonstrating is the fact that a global object (defined in the same translation unit) will be constructed before main is entered, and destroyed after main exits.
Be aware that when such a global object is being constructed, std::cout may not exist yet (and when it's being destroyed, std::cout may no longer exist), so any printing you do just about has to be via C functions like printf.

Answer 2

Another atrocious idea, just for the fun of it:
#include <iostream>
using namespace std;
#define main real_main
int main()
{
cout << "is the first day\n";
}
#undef main
int main()
{
cout << "Monday\n";
int res = real_main();
cout << "of the week\n";
return res;
}
Another version which does not rely on preprocessor foo would be to use global static object construction and destruction. This is safe, since apparently the standard guarantees that std::cout (and friends) is initialized and destroyed before/after all user code:
#include <iostream>
using namespace std;
struct Homework
{
Homework()
{
cout << "Monday\n";
}
~Homework()
{
cout << "of the week\n";
}
} hw;
int main()
{
cout << "is the first day\n";
}

Answer 3

Seems like a poor homework question. I can see no way to print other outputs without modifying the main method - unless you created another main method to override this?! The code provide is wrong as well - it should return 0 as main is expected to return an integer.

Answer 4

What about this?
#include <iostream>
#include <cstdlib>
using namespace std;
struct Foo
{
Foo()
{
cout << "Monday\nis the first day\nof the week\n";
exit(0);
}
} X;
int main()
{
cout << "is the first day\n";
}
Update
Ok, you may use name 'cout' in main func like some object not from iostream:
#include <iostream>
#include <string>
class Foo
{
public:
void operator <<( const std::string & s )
{
std::cout << "Monday\n" << s << "of the week";
}
} cout;
int main()
{
cout << "is the first day\n";
}

Answer 5

There are at least a couple of ways you can do this.
You can replace the meaning of cout.
You can make things happen before and after main is called.
Redefining cout:
#include <iostream>
class MyCout {};
void operator<<(MyCout& myCout, const char* message) {
std::cout << "Monday\n";
std::cout << message;
std::cout << "of the week\n";
}
MyCout cout;
int main()
{
cout << "is the first day\n";
}
To making things happen before and after main, you can create a static object. Their constructor is called before main, and the destructor afterwards:
#include <iostream>
class PrintExtras {
public:
PrintExtras() {
std::cout << "Monday\n";
}
~PrintExtras() {
std::cout << "of the week\n";
}
};
PrintExtras printExtras;
using std::cout;
int main()
{
cout << "is the first day\n";
}

Answer 6

I think you should make an operator overload for the output stream.

Answer 7

Think of things that happen before entry into main or after exit from main.
Early in a program you typically have initialization, at the end its counterpart.
What is the C++ idiom for those things?
How can you make those happen outside the body of main()?
What do you know about objects defined at namespace scope?
It really depends on where you are with your course, if you know about these things.
Alternative: The object used in main is only std::cout if you bring that name into the global namespace. Objects in namespaces other than ::std can also bear that name.