In the i(ANSI/ISO) standard does not include the previously available i(GNU)
extension ti(form()) (and ti(scan())) for stream objects. In this section the
construction of a class ti(oformstream) is described, which is derived from
    hi(derived class) ti(ostream) and does support tt(form()) and
ti(vform()). Analogously to tt(oformstream) a tt(class) ti(iscanstream) can be
developed, supporting tt(scan()) and ti(vscan()). The contruction of this
latter class is left as an i(exercise) to the reader.

    Here is the class interface and definition. It is annotated below:
        verbinclude(-a examples/oformstream.h)
    itemization(
    it() At 1 the class is defined: it is derived from tt(ostream), so it
inherits tt(ostream)'s capabilities.
    it() At 2 a simple constructor is defined. It expects a reference to a
tt(std::ostream) object.
    it() At 3 the member tt(form()) is declared. Its definition is given
shortly.
    )

    A program using the class tt(oformstream) is given in the next
example. It prints a well-known string and some marker text:
        verbinclude(-a examples/oformstream.cc)

    In the above example:
    itemization(
    it() At 1 the function tt(form()) is defined.
    it() At 2 the function ti(vsnprintf()) is given a buffer size of 0 and
tt(0) as the pointer to the buffer. According to the ti(ISO/IEC 9899:1999)
standard, the function tt(vsnprintf()) returns the number of required
characters for the formatted string (not including the final 0-valued
character) (see the tt(vsnprintf()) man page for details and possible
alternative implementations of tt(vsnprintf())).
    it() At 3 an ti(auto_ptr) is used to manage the dynamically
        hi(dynamic allocation) allocated buffer.
    it() At 4 the text is formatted.
    it() At 5 the content of the buffer
are written to the tt(ostream) base class, and the tt(oformstream) object is
returned.
    )
