basic_streambuf::pbackfail

Article
12/01/2015

A protected virtual member function that tries to put back an element into the input stream, then make it the current element (pointed to by the next pointer).

Syntax

      virtual int
      _
      type pbackfail(
   int_type _Meta = traits_type::eof( )
);

Parameters

_Meta
The character to insert into the buffer, or traits_type::eof.

Return Value

If the function cannot succeed, it returns traits_type::eof or throws an exception. Otherwise, it returns some other value. The default behavior is to return traits_type::eof.

Remarks

If _Meta compares equal to traits_type::eof, the element to push back is effectively the one already in the stream before the current element. Otherwise, that element is replaced by traits_type::to_char_type(_Meta). The function can put back an element in various ways:

If a putback position is available, it can store the element into the putback position and decrement the next pointer for the input buffer.
It can make a putback position available by allocating new or additional storage for the input buffer.
For a stream buffer with common input and output streams, it can make a putback position available by writing out, to some external destination, some or all of the elements between the beginning and next pointers for the output buffer.

Requirements

Header: <streambuf>

Namespace: std

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