std::basic_streambuf<CharT,Traits>::pbackfail
virtual int_type pbackfail( int_type c = Traits::eof() );
This function can only be called if any of the following condition is satisfied:
- gptr() is null,
- gptr() == eback(), or
- traits::eq(traits::to_char_type(c), gptr()[-1]) returns false.
This function is called by the public functions sungetc() and sputbackc() (which, in turn, are called by basic_istream::unget and basic_istream::putback) when either:
pbackfail() is called with no arguments). In this situation, the purpose of pbackfail() is to back up the get area by one character, if the associated character sequence allows this (e.g. a file-backed streambuf may reload the buffer from a file, starting one character earlier). pbackfail() is called with the character that needs to be put back). In this situation, the purpose of pbackfail() is to place the character c into the get area at the position just before basic_streambuf::gptr(), and, if possible, to modify the associated character sequence to reflect this change. This may involve backing up the get area as in the first variant.The default base class version of this function does nothing and returns Traits::eof() in all situations. This function is overridden by the derived classes: basic_stringbuf::pbackfail, basic_filebuf::pbackfail, strstreambuf::pbackfail, and is expected to be overridden by user-defined and third-party library stream classes.
[edit] Parameters
[edit] Return value
Traits::eof() in case of failure, some other value to indicate success. The base class version always fails.
[edit] Example
Reason: no example
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 32 | C++98 | the calling condition 'traits::eq(*gptr(),traits::to_char_type(c)) returns false' did not match the description of sputbackc() |
corrected to match the description |
[edit] See also
(virtual protected member function of
std::basic_filebuf<CharT,Traits>) [edit]
(virtual protected member function of
std::basic_stringbuf<CharT,Traits,Allocator>) [edit]
(virtual protected member function of
std::strstreambuf) [edit]