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From: Rune Allnor on 16 Jun 2008 08:27
Hi all.

Section 13.10.3 of the Josuttis book on the STL contains a
basic recipe on how to redirect output written to std::cout
to some other stream. However, the section contains a
cautionary remark that std::cout should be restored to its
initial state before program termination.

Is there a standard way to handle this safely? Some sort of
RAII pattern where the constructor redirects std::cout to some
destination and the destructor resets whatever was modified?

Rune

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From: Amal Pillai on 17 Jun 2008 04:44

> Is there a standard way to handle this safely? Some sort of
> RAII pattern where the constructor redirects std::cout to some
> destination and the destructor resets whatever was modified?

Well, does not your question contain the answer ? A simple wrapper
class like the one below (redirector) should work fine. Please note
that the implementation is not thread-safe nor does it check for
errors.

-Amal

// simplistic implementation, you might want to check the ofstream and
// throw exceptions and so on
class redirector {

std::streambuf* cout_buf_;
std::streambuf* cerr_buf_;

public:
redirector(std::ofstream& ofs)
: cout_buf_(0),
cerr_buf_(0) {

cout_buf_ = std::cout.rdbuf(ofs.rdbuf());
cerr_buf_ = std::cerr.rdbuf(ofs.rdbuf());
}

~redirector() {
std::cout.rdbuf(cout_buf_);
std::cerr.rdbuf(cerr_buf_);
}

};

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From: Ulrich Eckhardt on 17 Jun 2008 04:47
Rune Allnor wrote:
> Section 13.10.3 of the Josuttis book on the STL contains a
> basic recipe on how to redirect output written to std::cout
> to some other stream. However, the section contains a
> cautionary remark that std::cout should be restored to its
> initial state before program termination.
>
> Is there a standard way to handle this safely? Some sort of
> RAII pattern where the constructor redirects std::cout to some
> destination and the destructor resets whatever was modified?

Sure, using RAII works for this. I believe that Boost also contains a 'state
saver' utility class for IOStreams, which helps with this or actually does
this.

Uli

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