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2341. Inconsistency betweenbasic_ostream::seekp(pos) andbasic_ostream::seekp(off, dir)

Section: 31.7.6.2.5[ostream.seeks]Status:C++14Submitter: Marshall ClowOpened: 2013-10-21Last modified: 2017-07-05

Priority:0

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Discussion:

In 31.7.6.2.5[ostream.seeks], we have:

basic_ostream<charT,traits>& seekp(pos_type pos);

-3-Effects: Iffail() != true, executesrdbuf()->pubseekpos(pos, ios_base::out). In case of failure, the function callssetstate(failbit) (which may throwios_base::failure).

-4-Returns:*this.

basic_ostream<charT,traits>& seekp(off_type off, ios_base::seekdir dir);

-5-Effects: Iffail() != true, executesrdbuf()->pubseekoff(off, dir, ios_base::out).

-6-Returns:*this.

The first call is required to set thefailbit on failure, but the second is not

So (given two ostreams,os1 andos2) the following code (confusingly) works:

os1.seekp(-1);assert(os1.fail());os2.seekp(-1, std::ios_base::beg);assert(os2.good());

Note that the description ofbasic_istream<charT,traits>& seekg(off_type off, ios_base::seekdir dir) in 31.7.5.4[istream.unformatted] p43does require settingfailbit.

[Issaquah 2014-02-11: Move to Immediate]

Proposed resolution:

This wording is relative to N3797.

1. Modify 31.7.6.2.5[ostream.seeks]p5 as indicated:

   basic_ostream<charT,traits>& seekp(off_type off, ios_base::seekdir dir);

   -5-Effects: Iffail() != true, executesrdbuf()->pubseekoff(off, dir, ios_base::out).In case of failure, the function callssetstate(failbit) (which may throwios_base::failure).

   -6-Returns:*this.