g++: undefined reference

[everid]

       //main.cpp
      int puts ( const char * str );
      int main()
      {
      puts("Hello world\n");
      }

HI guys,
The above won't work in g++. But some one i know says it works in other compilers.
puts() is a function in C standard library.
So is there any option i have to use in order to make it work?
Thank you very much.

[Zhuge]

If it is in the C std library, then you shouldn't be declaring your own prototype. Considering there are no multiple definition errors, I think you are not including <stdio.h> (for C) or <cstdio> (for C++).

[everid]

Thank you for your help. But the requirement is that i can not use any header file. This is the problem of Thinking in C++ chapter 10 question 35.

[jsmith]

Ok, IMHO that's a stupid assignment.

namespace std {
    int puts( const char* );
}

[everid]

the problem is:
"Without including a header file, declare the function puts() from the Standard C Library. Call this function from main()."

I write:

namespace std{
  int puts(const char*);
}
main(){
  using namespace std;
  puts("h");
}

Then I got error:
In function `main': undefined reference to `std::puts(char const*)'
Why is that?
Thank you.

[jsmith]

You are not linking against the C++ runtime library for some reason. Don't know why your compiler is not including it by default. The code is otherwise correct and compiles and runs fine for me.