Redirect both cout and stdout to a string in C++ for Unit Testing

I'm working on getting some legacy code under unit tests and sometimes the only way to sense an existing program behavior is from the console output.

I see lots of examples online for how to redirect stdout to another file in C++, but is there a way I can redirect it to an in-memory stream so my tests don't have to rely on the disk?

I'd like to get anything that the legacy code sends to stdout into a std::string so I can easily .find on the output.

Edit

The legacy code is so bad that it users a mixture of cout << .. and printf. Here is what I have so far:

void TestSuite::setUp(void)
{
    oldStdoutBuf = std::cout.rdbuf();
    std::cout.rdbuf(consoleOutput.rdbuf());
}
void TestSuite::tearDown(void)
{
    std::cout.rdbuf(oldStdoutBuf);
}

The problem is that this does not capture output using printf. I would like something that gets both. Any ideas?