std::basic_spanbuf<CharT,Traits>::seekoff

 

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std::basic_spanbuf

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basic_spanbuf::seekoff (C++23)

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protected: pos_type seekoff( off_type off, std::ios_base::seekdir dir,                   std::ios_base::openmode which =                       std::ios_base::in | std::ios_base::out ) override;		(since C++23)

Repositions the next pointer to get and/or put area, if possible, to the position that corresponds to exactly off characters from beginning, end, or current position of the get and/or put area of the buffer.

Let n be the number of CharT elements in underlying buffer, or ​0​ when there is no underlying buffer, this function fails if

• the next pointer to the get and/or put area to reposition is null and the computed newoff (see below) is not zero, which may occur if there is no underlying buffer, or the *this is not opened in the mode required by which, or
• dir is std::ios_base::cur and both std::ios_base::in and std::ios_base::out are set in which, or
• the computed newoff is not representable in off_type, less than zero, or greater than n.

newoff is computed as below:

• If dir is std::ios_base::beg, newoff is off.
• If dir is std::ios_base::cur, newoff is
  • pptr() - pbase() + off if std::ios_base::out is set in which, or
  • gptr() - eback() + off if std::ios_base::in is set in which.
• If dir is std::ios_base::end, newoff is
  • pptr() - pbase() + off if std::ios_base::out but not std::ios_base::in is set in the open mode of *this,
  • otherwise, off + n.

This function repositions the next pointer to get and/or put area to pbuf + newoff on success if std::ios_base::in and/or std::ios_base::out is correspondingly set in which, where pbuf is the pointer to the beginning of the underlying buffer, or the null pointer value if there is no underlying buffer.

Parameters

off	-	relative position to set the next pointer(s) to
dir	-	defines base position to apply the relative offset to. It can be one of the following constants: Constant Explanation beg the beginning of a stream end the ending of a stream cur the current position of stream position indicator
which	-	defines whether the input sequences, the output sequence, or both are affected. It can be one or a combination of the following constants: Constant Explanation in affect the input sequence out affect the output sequence

Return value

pos_type(newoff) on success, pos_type(off_type(-1)) on failure.

See also

seekoff [virtual]	repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function of std::basic_stringbuf<CharT,Traits,Allocator>)
seekoff [virtual]	repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function of std::strstreambuf)