[fpos.operations]

An fpos type specifies file position information.

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

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 141 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 141 — 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]