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+[fpos]
+
+# 31 Input/output library [[input.output]](./#input.output)
+
+## 31.5 Iostreams base classes [[iostreams.base]](iostreams.base#fpos)
+
+### 31.5.3 Class template fpos [fpos]
+
+#### [31.5.3.1](#general) General [[fpos.general]](fpos.general)
+
+[ð](#lib:fpos)
+
+namespace std {template<class stateT> class fpos {public:// [[fpos.members]](#members "31.5.3.2 Members"), members stateT state() const; void state(stateT); private: stateT *st*; // *exposition only*};}
+
+#### [31.5.3.2](#members) Members [[fpos.members]](fpos.members)
+
+[ð](#lib:state,fpos)
+
+`void state(stateT s);
+`
+
+[1](#members-1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L1659)
+
+*Effects*: Assigns s to *st*[.](#members-1.sentence-1)
+
+[ð](#lib:state,fpos_)
+
+`stateT state() const;
+`
+
+[2](#members-2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L1670)
+
+*Returns*: Current value of *st*[.](#members-2.sentence-1)
+
+#### [31.5.3.3](#operations) Requirements [[fpos.operations]](fpos.operations)
+
+[1](#operations-1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L1677)
+
+An fpos type specifies file position information[.](#operations-1.sentence-1)
+
+It holds a state object
+whose type is equal to the template parameter stateT[.](#operations-1.sentence-2)
+
+Type stateT shall meet
+the [*Cpp17DefaultConstructible*](utility.arg.requirements#:Cpp17DefaultConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [30](utility.arg.requirements#tab:cpp17.defaultconstructible "Table 30: Cpp17DefaultConstructible requirements")),[*Cpp17CopyConstructible*](utility.arg.requirements#:Cpp17CopyConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [32](utility.arg.requirements#tab:cpp17.copyconstructible "Table 32: Cpp17CopyConstructible requirements (in addition to Cpp17MoveConstructible)")),[*Cpp17CopyAssignable*](utility.arg.requirements#:Cpp17CopyAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [34](utility.arg.requirements#tab:cpp17.copyassignable "Table 34: Cpp17CopyAssignable requirements (in addition to Cpp17MoveAssignable)")), and[*Cpp17Destructible*](utility.arg.requirements#:Cpp17Destructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [35](utility.arg.requirements#tab:cpp17.destructible "Table 35: Cpp17Destructible requirements")) requirements[.](#operations-1.sentence-3)
+
+If is_trivially_copy_constructible_v<stateT> is true,
+then fpos<stateT> has a trivial copy constructor[.](#operations-1.sentence-4)
+
+If is_trivially_copy_assignable_v<stateT> is true,
+then fpos<stateT> has a trivial copy assignment operator[.](#operations-1.sentence-5)
+
+If is_trivially_destructible_v<stateT> is true,
+then fpos<stateT> has a trivial destructor[.](#operations-1.sentence-6)
+
+All specializations of fpos meet
+the [*Cpp17DefaultConstructible*](utility.arg.requirements#:Cpp17DefaultConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]"),[*Cpp17CopyConstructible*](utility.arg.requirements#:Cpp17CopyConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]"),[*Cpp17CopyAssignable*](utility.arg.requirements#:Cpp17CopyAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]"),[*Cpp17Destructible*](utility.arg.requirements#:Cpp17Destructible "16.4.4.2 Template argument requirements [utility.arg.requirements]"),
+and [*Cpp17EqualityComparable*](utility.arg.requirements#:Cpp17EqualityComparable "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [28](utility.arg.requirements#tab:cpp17.equalitycomparable "Table 28: Cpp17EqualityComparable requirements")) requirements[.](#operations-1.sentence-7)
+
+In addition, the expressions shown in Table [141](#tab:fpos.operations "Table 141: Position type requirements") are valid and have the indicated semantics[.](#operations-1.sentence-8)
+
+In that table,
+
+- [(1.1)](#operations-1.1)
+
+P refers to a specialization of fpos,
+
+- [(1.2)](#operations-1.2)
+
+p and q refer to values
+of type P or const P,
+
+- [(1.3)](#operations-1.3)
+
+pl and ql refer to modifiable lvalues of type P,
+
+- [(1.4)](#operations-1.4)
+
+O refers to type streamoff, and
+
+- [(1.5)](#operations-1.5)
+
+o and o2 refer to values
+of type streamoff or const streamoff[.](#operations-1.sentence-9)
+
+Table [141](#tab:fpos.operations) — Position type requirements [[tab:fpos.operations]](./tab:fpos.operations)  
+
+| [ð](#tab:fpos.operations-row-1)<br>**Expression** | **Return type** | **Operational** | **Assertion/note** |
+| --- | --- | --- | --- |
+| [ð](#tab:fpos.operations-row-2) |  | **semantics** | **pre-/post-condition** |
+| [ð](#tab:fpos.operations-row-3)<br>P(o) | P | converts from offset | *Effects*: Value-initializes the state object[.](#tab:fpos.operations-row-3-column-4-sentence-1) |
+| [ð](#tab:fpos.operations-row-4)<br>P p(o);   P p = o; |  |  | *Effects*: Value-initializes the state object[.](#tab:fpos.operations-row-4-column-4-sentence-1)<br>   *Postconditions*: p == P(o) is true[.](#tab:fpos.operations-row-4-column-4-sentence-2) |
+| [ð](#tab:fpos.operations-row-5)<br>P() | P | P(0) |  |
+| [ð](#tab:fpos.operations-row-6)<br>P p; |  | P p(0); |  |
+| [ð](#tab:fpos.operations-row-7)<br>O(p) | streamoff | converts to offset | P(O(p)) == p |
+| [ð](#tab:fpos.operations-row-8)<br>p == q | bool |  | *Remarks*: For any two values o and o2,  if p is obtained  from o converted to P or  from a copy of such P value and  if q is obtained  from o2 converted to P or  from a copy of such P value,  then p == q is true  only if o == o2 is true[.](#tab:fpos.operations-row-8-column-4-sentence-1) |
+| [ð](#tab:fpos.operations-row-9)<br>p != q | bool | !(p == q) |  |
+| [ð](#tab:fpos.operations-row-10)<br>p + o | P | + offset | *Remarks*: With ql = p + o;, then: ql - o == p |
+| [ð](#tab:fpos.operations-row-11)<br>pl += o | P& | += offset | *Remarks*: With ql = pl; before the +=, then:  pl - o == ql |
+| [ð](#tab:fpos.operations-row-12)<br>p - o | P | - offset | *Remarks*: With ql = p - o;, then: ql + o == p |
+| [ð](#tab:fpos.operations-row-13)<br>pl -= o | P& | -= offset | *Remarks*: With ql = pl; before the -=, then:  pl + o == ql |
+| [ð](#tab:fpos.operations-row-14)<br>o + p | convertible to P | p + o | P(o + p) == p + o |
+| [ð](#tab:fpos.operations-row-15)<br>p - q | streamoff | distance | p == q + (p - q) |
+
+[2](#operations-2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L1790)
+
+Stream operations that return a value of typetraits::pos_type returnP(O(-1)) as an invalid value to signal an error[.](#operations-2.sentence-1)
+
+If this value is used as an argument to anyistream,ostream,
+orstreambuf member
+that accepts a value of typetraits::pos_type then the behavior of that function is undefined[.](#operations-2.sentence-2)