count(3C++)

Synopsis

   #include <stddef.h>        
   

   template<class T>
   ptrdiff_t count(
        const T& val,
        const T* b,
        const T* e       
   );       
   template <class T>  
   ptrdiff_t count_r(         
        int (*rel)(const T*,const T*),
        const T& val,    
        const T* b,   
        const T* e  
   );   
   template <class T>  
   ptrdiff_t count_p(       
        int (*pred)(const T*),     
        const T* b,          
        const T* e 
   );

Assumptions

(1) For the plain version, T::operator== defines an equivalence relation on T.

(2) For the relational version, rel defines an equivalence relation on T.

Description

These functions count elements that satisfy some criterion.

   template <class T>
   ptrdiff_t count(
       const T& val,
       const T* b,
       const T* e
       );

Counts elements equal to val, as determined by T::operator==.

   template <class T>
   ptrdiff_t count_r(
       int (*rel)(const T*,const T*),
       const T& val,
       const T* b,
       const T* e
       );

Like count, but uses rel to test for equality. That is, if p is a pointer into the array, then *p is counted if rel(p,&val)==0.

   template <class T>
   ptrdiff_t count_p(
       int (*pred)(const T*),
       const T* b,
       const T* e
   );

Counts elements that satisfy the predicate. That is, if p is a pointer into the array, then *p is counted if pred(p) is true.

Complexity

If N is the size of the array, then complexity is O(N). Exactly N tests of the relation are done.

Notes

Because a Block (see Block(3C++)) can always be used wherever an array is called for, Array Algorithms can also be used with Blocks. In fact, these two components were actually designed to be used together.

References

   Array_alg(3C++)
   Block(3C++)