# std::discard_block_engine

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< cpp‎ | numeric‎ | random

Defined in header `<random>` |  |
template< class Engine, std::size_t P, std::size_t R > class discard_block_engine; |  | (since C++11)

`discard_block_engine` is a pseudo-random number engine adaptor that discards a certain amount of data produced by the base engine. From each block of size P generated by the base engine, the adaptor keeps only R numbers, discarding the rest.

### Template parameters

Engine | - | the type of the wrapped engine.
P | - | the size of a block. Expected that \(\small{P>0}\)P > 0.
R | - | the number of used numbers per block. Expected that \(\small{0<R\le P}\)0 < R ≤ P.
Type requirements
- `Engine` must meet the requirements of RandomNumberEngine.

### Member types

Member type | Definition
`result_type` (C++11) | `Engine::result_type`

### Member functions

(constructor) (C++11) | constructs the engine adaptor (public member function)
seed (C++11) | sets the state of the underlying engine (public member function)
base (C++11) | returns the underlying engine (public member function)

##### Generation

operator() (C++11) | advances the state of the underlying engine and returns the generated value (public member function)
discard (C++11) | advances the adaptor's state by a specified amount (public member function)

##### Characteristics

min [static] (C++11) | gets the smallest possible value in the output range of the underlying engine. (public static member function)
max [static] (C++11) | gets the largest possible value in the output range of the underlying engine. (public static member function)

### Non-member functions

operator==operator!= (C++11)(C++11)(removed in C++20) | compares the internal states of the adaptors and underlying engines (function)
operator<<operator>> (C++11) | performs stream input and output on pseudo-random number engine adaptor (function)

### Member constants

constexpr size_t block_size [static] (C++11) | the size of the block, P (public static member constant)
constexpr size_t used_block [static] (C++11) | the number of used numbers per block, R (public static member constant)

### Example

| This section is incomplete Reason: no example

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