Standard Template Library Programmer's Guide

There exist some types U and V such that Pair provides the same interface as a pair . [1]

unary_function

All of select2nd 's members are defined in the Adaptable Unary Function requirements. Select2nd does not introduce any new members.

[1] Pair is not actually required to be a pair , but merely to support the same interface as pair . In almost all cases the template parameter will be a pair , but it is occasionally useful for it to be something else. One example is a struct that has the members first , second , and third .

identity , select1st , project1st , project2nd

Category: functors

Component type: type

Subtractive_rng is a Random Number Generator based on the subtractive method [1]. It is a Unary Function: it takes a single argument N , an unsigned int , and returns an unsigned int that is less than N . Successive calls to the same subtractive_rng object [2] yield a pseudo-random sequence.

int main() {

subtractive_rng R;

for (int i = 0; i < 20; ++i) cout << R(5) << ' ';

cout << endl;

}

// The output is 3 2 3 2 4 3 1 1 2 2 0 3 4 4 4 4 2 1 0 0

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h. This function object is an SGI extension; it is not part of the C++ standard.

None.

Random Number Generator, Adaptable Unary Function

None.

unary_function

These members are not defined in the Adaptable Unary Function requirements, but are specific to subtractive_rng .

[1] See section 3.6 of Knuth for an implementation of the subtractive method in FORTRAN. Section 3.2.2 of Knuth analyzes this class of algorithms. (D. E. Knuth, The Art of Computer Programming. Volume 2: Seminumerical Algorithms , second edition. Addison-Wesley, 1981.)

[2] Note that the sequence produced by a subtractive_rng is completely deterministic, and that the sequences produced by two different subtractive_rng objects are independent of each other. That is: if R1 is a subtractive_rng , then the values returned when R1 is called depend only on R1 's seed and on the number of times that R1 has been called. Calls to other subtractive_rng objects are irrelevant. In implementation terms, this is because the class subtractive_rng contains no static members.

Random Number Generator

Categories: functors, adaptors

Component type: type

Binder1st is a function object adaptor: it is used to transform an adaptable binary function into an adaptable unary function. Specifically, if f is an object of class binder1st , then f(x) returns F(c, x) , where F is an object of class AdaptableBinaryFunction and where c is a constant. Both F and c are passed as arguments to binder1st 's constructor. [1]

The easiest way to create a binder1st is not to call the constructor explicitly, but instead to use the helper function bind1st .

Finds the first nonzero element in a list.

list L;

…

list::iterator first_nonzero = find_if(L.begin(), L.end(), bind1st(not_equal_to(), 0));

assert(first_nonzero == L.end() || *first_nonzero != 0);

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h.

Adaptable Unary Function

AdaptableBinaryFunction must be a model of Adaptable Binary Function.

unary_function

These members are not defined in the Adaptable Unary Function requirements, but are specific to binder1st .