[#BloombergLP-bdlde-Utf8CheckingInStreamBufWrapper-seekoff]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlde.adoc[bdlde]::xref:BloombergLP/bdlde/Utf8CheckingInStreamBufWrapper.adoc[Utf8CheckingInStreamBufWrapper]::seekoff
:relfileprefix: ../../../
:mrdocs:

Move the position associated with this object according to the specified `offset` and `whence`:

== Synopsis

Declared in `<bdlde_utf8checkinginstreambufwrapper.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
virtual
pos_type
seekoff(
    off_type offset,
    std::ios_base::seekdir whence,
    std::ios_base::openmode mode) override;
----

== Description

* If `whence` is `bsl::ios_base::beg`, set the position to `offset` bytes from the beginning. * If `whence` is `bsl::ios_base::cur`, advance the position by `offset` bytes (note that `offset` is signed). * `whence == bsl::ios_base::end` is unsupported and a seek fail will result.

A seek can fail if

* the object was already in a failed seek state and the seek was not an absolute seek to the beginning, * the object is not bound to a held `streambuf`, * `whence` is not `bsl::ios_base::beg` or `bsl::ios_base::cur`, * the destination is negative, * the destination is forward of the current position, or * a seek on the held `streambuf` is necessary and that `streambuf` does not support seeking,

which will put the object into a `failed seek state`. When the object is in a failed seek state, `errorStatus()` will equal `k_SEEK_FAIL` and the object will no longer have a valid position, meaning that input and relative seeks will fail, until the object is made to recover by either calling `reset` or an absolute seek to position 0.

If a seek is performed on the held `streambuf`, the specified `mode` will be propagated to it. The behavior is undefined unless `bsl::ios_base::in` is set in `mode`. Note that this function is forwarded to by the public method `pubseekoff` in the base class.

`seekoff(0, bsl::ios_base::cur, mode)` is permissible whether the held `streambuf` is seekable or not and will never result in a seek on the held `streambuf`, returning the position in terms of the held `streambuf` if that `streambuf` is seekable and returning the position relative to when the held `streambuf` was bound to this object otherwise.

Some non‐zero seeks will be performed without a seek on the held `streambuf`, but there is no simple way for the client to predict when this will be the case.


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