[#BloombergLP-bdls-FdStreamBuf-pbackfail]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdls.adoc[bdls]::xref:BloombergLP/bdls/FdStreamBuf.adoc[FdStreamBuf]::pbackfail
:relfileprefix: ../../../
:mrdocs:

If the optionally specified `c` is not given, move the current input position back one character and return the character at that position. Otherwise specify a value for `c` other than `traits_type::eof`. If `c` is equal to the previous character in the read buffer, the behavior is the same as if `eof()` was passed. If `c` is not eof and is not equal to the previous character in the putback buffer push the character `c` is back into the input buffer, if possible. Return the backed up character on success and `traits_type::eof()` otherwise. If the input buffer is readonly, or `gptr()` is already at the beginning of the input buffer, this object enters `INPUT_PUTBACK_MODE` and `c` is stuffed back into the putback buffer. Note that only `PBACK_BUF_SIZE` characters can be backed up into the putback buffer, if this limit is exceeded, `traits_type::eof()` will be returned. Also note that this method is called by public methods `sputbackc` or `sungetc` in the base class, and only when simply decrementing the current position in the input buffer won't satisfy the request, either because `c` doesn't match the previously input character, or because the input position is already at the beginning of the input buffer.

== Synopsis

Declared in `<bdls_fdstreambuf.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
virtual
int_type
pbackfail(int_type c = traits_type::eof()) override;
----


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