partial_ordering Class

Detailed Description

A value of type Qt::partial_ordering is typically returned from a three-way comparison function. Such a function compares two objects, establishing whether they are ordered and, if so, their ordering. It uses this return type to indicate that the ordering is partial; that is, not all pairs of values are ordered.

Qt::partial_ordering has four values, represented by the following symbolic constants:

• less represents that the left operand is less than the right;
• equivalent represents that the two operands are equivalent;
• greater represents that the left operand is greater than the right;
• unordered represents that the two operands are not ordered.

Qt::partial_ordering is idiomatically used by comparing an instance against a literal zero, for instance like this:

 // given a, b, c, d as objects of some type that allows for a 3-way compare,
 // and a compare function declared as follows:

 Qt::partial_ordering compare(T lhs, T rhs); // defined out-of-line
 ~~~

 Qt::partial_ordering result = compare(a, b);
 if (result < 0) {
     // a is less than b
 }

 if (compare(c, d) >= 0) {
     // c is greater than or equal to d
 }

Comparing Qt::partial_ordering::unordered against literal 0 always returns a false result.