using string in <iostream> and <string>

[Ly59GNh0]

A rather simple question, but is...

#include <iostream>

int main ()
{
    std::string a("Hello world!");
    std::cout << a << std::endl;
    return 0;
}

different from...

#include <iostream>
#include <string>

int main ()
{
    std::string a("Hello world!");
    std::cout << a << std::endl;
    return 0;
}

?

And if not, why does the book I'm reading insist that I include both iostream and string, when just iostream seems to be working just fine?

[Bazzy]

You should always include the header files containing the definitions of the class that you are using because if the implementation of your standard library includes <string> in <iostream>, other compilers with different library implementations may not have this.
When you #include a standard header you are just typing an extra line with no other issues as headers are guarded.
So: include all the headers that you need

[Ly59GNh0]

Ahh, so it's compiler specific? I just assumed iostream was the same for everyone.
Thanks, that cleared it up. :)