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Full Discussion: Arrays in C++
Top Forums Programming Arrays in C++ Post 302584573 by John Tate on Friday 23rd of December 2011 05:03:25 PM
Old 12-23-2011
Arrays in C++
I've noticed something interesting in C++ programming. I've always done tricky stuff with pointers and references to have functions deal with arrays. Doing exercises again out of a C++ book has shown me an easier way, I didn't even know was there. It's weird to me.

When dealing with arrays, it seems if I pass an array to a function although I cannot return an array - if the array is changed it changes for the whole program. The array is seemingly global. Hence this code works (GCC 4.7)...

Code:
#include <iostream>

using namespace std;

int read_inputs(double inputs[], int capacity) {
    int current_size = 0;
    cout << "Please enter values, Q to quit:"<<endl;
    bool more = true;
    while (more)
    {
        double input;
        cin >> input;
        if (cin.fail()) {
            more = false;
        } else if (current_size < capacity) {
            inputs[current_size] = input;
            current_size++;
        }
    }
    return current_size;
}

void multiply(double values[], int size, double factor)
{
    for (int i = 0; i < size; i++)
    {
        values[i]=values[i] * factor;
    }
}

void print(double values[], int size)
{
    for (int i = 0; i < size; i++)
    {
        if (i > 0) {cout << ", ";}
        cout << values[i];
    }
    cout << endl;
}

int main() {
    const int CAPACITY = 1000;
    double values[CAPACITY];
    int size = read_inputs(values, CAPACITY);
    print(values, size);
    multiply(values, size, 2);
    print(values, size);

    return 0;
}

 

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LEARN ABOUT HPUX

judy

Judy(3X)																  Judy(3X)

NAME

       Judy functions - C libraries for creating and accessing dynamic arrays

SYNOPSIS

       Judy1  - maps an Index (word) to a bit
       JudyL  - maps an Index (word) to a word
       JudySL - maps an Index (string) to a word

DESCRIPTION

       The  Judy family of functions supports fully dynamic arrays.  These arrays may be indexed by a 32- or 64-bit word (depending on the proces-
       sor) or a string.  A dynamic array that is sparsely populated can be thought of as a mapping function.  There are 3 different Judy mappings
       currently supported:
       Judy1 maps an Index (word) to a bit.
       JudyL maps an Index (word) to a word.
       JudySL maps an Index (string) to a word.

       For  Judy1  functions and JudyL functions, Index should be declared as a Word_t type.  Word_t is defined in the Judy.h header file as a 32-
       or 64-bit unsigned native integer, and has the same number of bits as a pointer.

       For JudySL functions, each index is a null-terminated string.

       Judy arrays are both speed- and memory-efficient, with no tuning or configuration required, across a wide range of index set types (sequen-
       tial,  periodic,  clustered, random).  Judy's speed and memory usage are typically better than other data storage models such as skiplists,
       binary trees, b-trees, or even hashing, and improves with very large data sets.

       A Judy array is created merely by defining a null pointer and then storing (inserting) the first element into the array under that pointer.
       The memory used by a Judy array is proportional to the population (number of elements).

       Judy has two Application Program Interfaces (APIs): a C macro interface, and a function call interface.	Because the macro forms are faster
       and have a simpler error handling interface than the equivalent functions, they are the preferred way of calling the Judy functions.

       Since an initial (empty) Judy array is represented by a null pointer, it is possible to construct an array of Judy arrays.  In other words,
       a Judy array's values (except Judy1) can be pointers to other Judy arrays.

AUTHOR

       Judy was invented and implemented by Hewlett-Packard.  (Note:  Judy is named for the inventor's sister.)

FILES

       Locations of interest include:

       Documents, including HTML versions of the manual entries.

       Demonstration program source files.

SEE ALSO

       Judy1(3X), JudyL(3X), JudySL(3X),
       the Judy website, http://www.hp.com/go/judy/, for more information and Application Notes.

																	  Judy(3X)
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