Книга: Standard Template Library Programmer



Category: functors

Component type: type


Logical_or<T> is a function object; specifically, it is an Adaptable Binary Predicate, which means it is a function object that tests the truth or falsehood of some condition. If f is an object of class logical_and<T> and x and y are objects of class T (where T is convertible to bool) then f(x,y) returns true if and only if either x or y is true. [1]


Finds the first instance of either ' ' or 'n' in a string.

char str[MAXLEN];

const char* wptr = find_if(str, str + MAXLEN, compose2(logical_or<bool>(), bind2nd(equal_to<char>(), ' '), bind2nd(equal_to<char>(), 'n')));
assert(wptr == str + MAXLEN || *wptr == ' ' || *wptr == 'n');


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

Template parameters

Parameter Description
T The type of logical_or's arguments

Model of

Adaptable Binary Predicate, DefaultConstructible

Type requirements

T must be convertible to bool.

Public base classes

binary_function<T, T, bool>


Member Where defined Description
first_argument_type Adaptable Binary Function The type of the first argument: T
second_argument_type Adaptable Binary Function The type of the second argument: T
result_type Adaptable Binary Function The type of the result: bool
bool operator()(const T& x, const T& y) const Binary Function Function call operator. The return value is x || y.
logical_or() Default Constructible The default constructor.

New members

All of logical_or's members are defined in the Adaptable Binary Function and Default Constructible requirements. Logical_or does not introduce any new members.


[1] Logical_and and logical_or are not very useful by themselves. They are mainly useful because, when combined with the function object adaptor binary_compose, they perform logical operations on other function objects.

See also

The function object overview, logical_and, logical_not.

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