Printf directly to an MFC CString

This is a function which makes it easy to elegantly create a temporary char* or CString and pass it as an argument, without having to explicitly create a temporary variable.

A common problem: You need to format a string and then pass it to some function, but it seems like a silly nuisance to have to explicitly create a temporary buffer to hold the string, format into that buffer, and then call the function.  For example, you see code all the time that looks like this:

if (some condition)
{
    CString str;
    str.Format( "Important info: %d %s", n, s );
    SomeFunction(str);
}

It would be so much cleaner to be able to write your code something like this:

if (some condition)
    SomeFunction("Important info: %d %s", n, s);

However, that would require having a varargs constructor for SomeFunction -- and for every other similar function which takes a string as input.

But this function, StrPrintf, allows you to write the above example like this, which is almost as good:

if (some condition)
    SomeFunction( StrPrintf("Important info: %d %s", n, sz) );

This creates a temporary object on the stack of type CString; formats the specified string into it; passes either a CString or a (const char*) to the function; and then deletes the temporary object automatically.

[Whether a CString or a (const char*) gets passed depends on the prototype of SomeFunction.  CString supports an implicit cast to (const char*) -- or to be more precise, to (LPCTSTR).  So the above line of code will implicitly cast the CString to a (const char*) if necessary.]

Here's another example:  This code...

if (FAILED(hr))
{
    CString s;
    s.Format("Error %X", hr);
    AfxMessageBox(s);
}

...becomes this:

if (FAILED(hr))
    AfxMessageBox( StrPrintf("Error %X", hr) );

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