[fpos.operations]

An fpos type specifies file position information.

It holds a state object whose type is equal to the template parameter stateT.

Type stateT shall meet the Cpp17DefaultConstructible (Table 30), Cpp17CopyConstructible (Table 32), Cpp17CopyAssignable (Table 34), and Cpp17Destructible (Table 35) requirements.

If is_trivially_copy_constructible_v<stateT> is true, then fpos<stateT> has a trivial copy constructor.

If is_trivially_copy_assignable_v<stateT> is true, then fpos<stateT> has a trivial copy assignment operator.

If is_trivially_destructible_v<stateT> is true, then fpos<stateT> has a trivial destructor.

In addition, the expressions shown in Table 136 are valid and have the indicated semantics.

In that table,

(1.1)
P refers to a specialization of fpos,
(1.2)
p and q refer to values of type P or const P,
(1.3)
pl and ql refer to modifiable lvalues of type P,
(1.4)
O refers to type streamoff, and
(1.5)
o and o2 refer to values of type streamoff or const streamoff.

Table 136: Position type requirements [tab:fpos.operations]

🔗	Expression	Return type	Operational	Assertion/note
🔗			semantics	pre-/post-condition
🔗	P(o)	P	converts from offset	Effects: Value-initializes the state object.
🔗	P p(o); P p = o;			Effects: Value-initializes the state object. Postconditions: p == P(o) is true.
🔗	P()	P	P(0)
🔗	P p;		P p(0);
🔗	O(p)	streamoff	converts to offset	P(O(p)) == p
🔗	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.
🔗	p != q	bool	!(p == q)
🔗	p + o	P	+ offset	Remarks: With ql = p + o;, then: ql - o == p
🔗	pl += o	P&	+= offset	Remarks: With ql = pl; before the +=, then: pl - o == ql
🔗	p - o	P	- offset	Remarks: With ql = p - o;, then: ql + o == p
🔗	pl -= o	P&	-= offset	Remarks: With ql = pl; before the -=, then: pl + o == ql
🔗	o + p	convertible to P	p + o	P(o + p) == p + o
🔗	p - q	streamoff	distance	p == q + (p - q)

31 Input/output library [input.output]