iterator Modiﬁer

| OPENMP API Specification: "Version 5.2 -- GIT rev 95b2e3a44"

3.2.6 iterator Modiﬁer

Modiﬁers


Name	Modiﬁes	Type	Properties

iterator	locator-list	Complex, name: iterator Arguments: iterator-speciﬁer OpenMP expression (repeatable)	unique

Clauses

An iterator modiﬁer is a unique, complex modiﬁer that deﬁnes a set of iterators, each of which is an iterator-identiﬁer and an associated set of values. An iterator-identiﬁer expands to those values in the clause argument for which it is speciﬁed. Each member of the modiﬁer-parameter-speciﬁcation list of an iterator modiﬁer is an iterator-speciﬁer with this format:

 
[ iterator-type ]  iterator-identiﬁer = range-speciﬁcation

 
[ iterator-type :: ] iterator-identiﬁer = range-speciﬁcation

where:

iterator-identiﬁer is a base-language identiﬁer.
iterator-type is a type that is permitted in a type-name list.
range-speciﬁcation is of the form begin:end[:step], where begin and end are expressions for which their types can be converted to iterator-type and step is an integral expression.

In an iterator-speciﬁer, if the iterator-type is not speciﬁed then that iterator is of int type.

In an iterator-speciﬁer, if the iterator-type is not speciﬁed then that iterator has default integer type.

In a range-speciﬁcation, if the step is not speciﬁed its value is implicitly deﬁned to be 1.

An iterator only exists in the context of the clause argument that it modiﬁes. An iterator also hides all accessible symbols with the same name in the context of that clause argument.

The use of a variable in an expression that appears in the range-speciﬁcation causes an implicit reference to the variable in all enclosing constructs.

The values of the iterator are the set of values i₀, …, i_N−1 where:

i₀ = (iterator-type) begin;
i_j = (iterator-type) (i_j−1 + step), where j ≥ 1; and
if step > 0,
- i₀ < (iterator-type) end;
- i_N−1 < (iterator-type) end; and
- (iterator-type) (i_N−1 + step) ≥ (iterator-type) end;
if step < 0,
- i₀ > (iterator-type) end;
- i_N−1 > (iterator-type) end; and
- (iterator-type) (i_N−1 + step) ≤ (iterator-type) end.

The values of the iterator are the set of values i₁, …, i_N where:

i₁ = begin;
i_j = i_j−1 + step, where j ≥ 2; and
if step > 0,
- i₁ ≤ end;
- i_N ≤ end; and
- i_N + step > end;
if step < 0,
- i₁ ≥ end;
- i_N ≥ end; and
- i_N + step < end.

The set of values will be empty if no possible value complies with the conditions above.

If an iterator-identiﬁer appears in a list-item expression of the modiﬁed argument, the eﬀect is as if the list item is instantiated within the clause for each member of the iterator value set, substituting each occurrence of iterator-identiﬁer in the list-item expression with the iterator value. If the iterator value set is empty then the eﬀect is as if the list item was not speciﬁed.

Restrictions

Restrictions to iterator modiﬁers are as follows:

The iterator-type must not declare a new type.
For each value i in an iterator value set, the mathematical result of i + step must be representable in iterator-type.

∙ The iterator-type must be an integral or pointer type. ∙ The iterator-type must not be const qualiﬁed.

∙ The iterator-type must be an integer type.
If the step expression of a range-speciﬁcation equals zero, the behavior is unspeciﬁed.
Each iterator-identiﬁer can only be deﬁned once in the modiﬁer-parameter-speciﬁcation.
Iterators cannot appear in the range-speciﬁcation.

Cross References

affinity clause, see Section 12.5.1
depend clause, see Section 15.9.5
from clause, see Section 5.9.2
map clause, see Section 5.8.3
to clause, see Section 5.9.1

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