Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/numeric/ratio/ratio multiply"

From cppreference.com
< cpp‎ | numeric‎ | ratio
(+)
 
m (fmt)
 
(12 intermediate revisions by 5 users not shown)
Line 1: Line 1:
−
{{cpp/title | ratio_multiply}}
+
{{cpp/title|ratio_multiply}}
−
{{cpp/numeric/ratio/sidebar}}
+
{{cpp/numeric/ratio/navbar}}
−
{{ddcl list begin}}
+
{{ddcl|header=ratio|since=c++11|1=
−
{{ddcl list header | ratio}}
+
−
{{ddcl list item | 1=
+
 
template< class R1, class R2 >
 
template< class R1, class R2 >
−
using ratio_multiply = /* unspecified */;
+
using ratio_multiply = /* see below */;
 
}}
 
}}
−
{{ddcl list end}}
 
  
−
The template alias {{tt|std::ratio_multiply}} denotes the result of multiplying two exact rational fractions represented by the {{cpp|std::ratio}} instances {{tt|R1}} and {{tt|R2}}. The result a {{cpp|std::ratio}} instance {{tt|std::ratio<Num, Denom>}} where {{cpp|1=Num == R1::num * R2::num}} and {{cpp|1=Denom == R1::den * R2::den}}.
+
The alias template {{tt|std::ratio_multiply}} denotes the result of multiplying two exact rational fractions represented by the {{lc|std::ratio}} specializations {{tt|R1}} and {{tt|R2}}.
  
−
===Member types===
+
The result is a {{lc|std::ratio}} specialization {{c|std::ratio<U, V>}}, such that given  {{c|1=Num == R1::num * R2::num}} and {{c|1=Denom == R1::den * R2::den}} (computed without arithmetic overflow), {{tt|U}} is {{c|std::ratio<Num, Denom>::num}} and {{tt|V}} is {{c|std::ratio<Num, Denom>::den}}.
−
{{tdcl list begin}}
+
−
{{tdcl list hitem | Member type | Definition}}
+
−
{{tdcl list item | {{tt|type}} | {{cpp|std::ratio<num, den>}}}}
+
−
{{tdcl list end}}
+
  
−
===Member constants===
+
===Notes===
−
{{dcl list begin}}
+
If {{tt|U}} or {{tt|V}} is not representable in {{lc|std::intmax_t}}, the program is ill-formed. If {{tt|Num}} or {{tt|Denom}} is not representable in {{lc|std::intmax_t}}, the program is ill-formed unless the implementation yields correct values for {{tt|U}} and {{tt|V}}.
−
{{dcl list mem sconst | nolink=true | num | {{cpp|constexpr}} value of type {{cpp|std::intmax_t}} equal to {{tt|sign(Num) * sign(Denom) * abs(Num) / gcd(Num, Denom)}} }}
+
 
−
{{dcl list mem sconst | nolink=true | den | {{cpp|constexpr}} value of type {{cpp|std::intmax_t}} equal to {{tt|abs(Denom) / gcd(Num, Denom)}} }}
+
The above definition requires that the result of {{c|std::ratio_multiply<R1, R2>}} be already reduced to lowest terms; for example, {{c|std::ratio_multiply<std::ratio<1, 6>, std::ratio<4, 5>>}} is the same type as {{c|std::ratio<2, 15>}}.
−
{{dcl list end}}
+
  
 
===Example===
 
===Example===
−
{{example cpp
+
{{example
−
|
+
|
−
| code=
+
|code=
 
#include <iostream>
 
#include <iostream>
 
#include <ratio>
 
#include <ratio>
 +
 
int main()
 
int main()
 
{
 
{
−
     typedef std::ratio<2, 3> two_third;
+
     using two_third = std::ratio<2, 3>;
−
     typedef std::ratio<1, 6> one_sixth;
+
     using one_sixth = std::ratio<1, 6>;
−
     typedef std::ratio_multiply<two_third, one_sixth> r;
+
     using product = std::ratio_multiply<two_third, one_sixth>;
−
     std::cout << "2/3 * 1/6 = " << r::num << '/' << r::den << '\n';
+
    static_assert(std::ratio_equal_v<product, std::ratio<13, 117>>);
 +
     std::cout << "2/3 * 1/6 = " << product::num << '/' << product::den << '\n';
 
}
 
}
−
| output=
+
|output=
 
2/3 * 1/6 = 1/9
 
2/3 * 1/6 = 1/9
 
}}
 
}}
 +
 +
===See also===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/numeric/ratio/dsc ratio_divide}}
 +
{{dsc end}}
 +
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 14:46, 20 March 2023

 
C++
 
Metaprogramming library
Type traits
Type categories
(C++11)
(C++14)  
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)  
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Type properties
(C++11)
(C++11)
(C++11)
(C++11)
(C++14)
(C++11)
(C++17)
(C++23)
(C++11)
(C++11)
(C++11)
(C++11)(until C++20*)
(C++11)(deprecated in C++20)
(C++11)
(C++11)
(C++20)
(C++20)
(C++23)
(C++17)
Type trait constants
(C++11)(C++17)(C++11)(C++11)
Metafunctions
(C++17)
(C++17)
(C++17)
Supported operations
Relationships and property queries
Type modifications
(C++11)(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Type transformations
(C++11)(deprecated in C++23)
(C++11)(deprecated in C++23)
(C++11)
(C++20)
(C++11)
(C++17)

(C++11)
(C++11)
(C++20)
(C++11)
(C++11)(until C++20*)(C++17)
(C++20)
Compile-time rational arithmetic
Compile-time integer sequences
(C++14)
 
Compile time rational arithmetic
(C++11)
Arithmetic
(C++11)
(C++11)
ratio_multiply
(C++11)
(C++11)
Comparison
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
 
Defined in header <ratio>
template< class R1, class R2 >
using ratio_multiply = /* see below */;
 (since C++11)

The alias template std::ratio_multiply denotes the result of multiplying two exact rational fractions represented by the std::ratio specializations R1 and R2.

The result is a std::ratio specialization std::ratio<U, V>, such that given Num == R1::num * R2::num and Denom == R1::den * R2::den (computed without arithmetic overflow), U is std::ratio<Num, Denom>::num and V is std::ratio<Num, Denom>::den.

[edit] Notes

If U or V is not representable in std::intmax_t, the program is ill-formed. If Num or Denom is not representable in std::intmax_t, the program is ill-formed unless the implementation yields correct values for U and V.

The above definition requires that the result of std::ratio_multiply<R1, R2> be already reduced to lowest terms; for example, std::ratio_multiply<std::ratio<1, 6>, std::ratio<4, 5>> is the same type as std::ratio<2, 15>.

[edit] Example

Run this code
#include <iostream>
#include <ratio>
 
int main()
{
    using two_third = std::ratio<2, 3>;
    using one_sixth = std::ratio<1, 6>;
    using product = std::ratio_multiply<two_third, one_sixth>;
    static_assert(std::ratio_equal_v<product, std::ratio<13, 117>>);
    std::cout << "2/3 * 1/6 = " << product::num << '/' << product::den << '\n';
}

Output: 

2/3 * 1/6 = 1/9

[edit] See also

(C++11)
 divides two ratio objects at compile-time
(alias template)[edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/ratio/ratio_multiply&oldid=149445"