[fpos] (original) (raw)

31 Input/output library [input.output]

31.5 Iostreams base classes [iostreams.base]

31.5.3 Class template fpos [fpos]

31.5.3.1 General [fpos.general]

namespace std { template<class stateT> class fpos { public: stateT state() const;void state(stateT);private: stateT st; };}

31.5.3.2 Members [fpos.members]

Effects: Assigns s to st.

Returns: Current value of st.

31.5.3.3 Requirements [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 139are valid and have the indicated semantics.

In that table,

P refers to a specialization of fpos,
p and q refer to values of type P or const P,
pl and ql refer to modifiable lvalues of type P,
O refers to type streamoff, and
o and o2 refer to values of type streamoff or const streamoff.

Table 139 — 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)

Stream operations that return a value of typetraits::pos_typereturnP(O(-1))as an invalid value to signal an error.

If this value is used as an argument to anyistream,ostream, orstreambuf member that accepts a value of typetraits::pos_typethen the behavior of that function is undefined.