Optional parameters: Difference between revisions

=={{header|C++}}==

This implementation only accepts function pointers for the comparators, and does not accept function objects, for simplicity.

<lang cpp>#include <vector>

#include <algorithm>

#include <string>

// helper comparator that is passed to std::sort()

template <class T>

struct sort_table_functor {

typedef bool (*CompFun)(const T &, const T &);

CompFun ordering;

int column;

bool reverse;

sort_table_functor(CompFun o, int c, bool r) :

ordering(o), column(c), reverse(r) { }

bool operator()(const std::vector<T> &x, const std::vector<T> &y) {

const T &a = x[column],

&b = y[column];

return reverse ? ordering(b, a)

: ordering(a, b);

}

};

// natural-order less-than comparator

template <class T>

bool myLess(const T &x, const T &y) { return x < y; }

// this is the function we call, which takes optional parameters

template <class T>

void sort_table(std::vector<std::vector<T> > &table,

int column = 0, bool reverse = false,

bool (*ordering)(const T &, const T &) = myLess) {

std::sort(table.begin(), table.end(),

sort_table_functor<T>(ordering, column, reverse));

}

#include <iostream>

// helper function to print our 3x3 matrix

template <class T>

void print_matrix(std::vector<std::vector<T> > &data) {

for () {

for (int j = 0; j < 3; j++)

std::cout << data[i][j] << "\t";

std::cout << std::endl;

}

}

// order in descending length

bool desc_len_comparator(const std::string &x, const std::string &y) {

return x.length() > y.length();

}

int main() {

std::string data_array[3][3] =

{

{"a", "b", "c"},

{"", "q", "z"},

{"zap", "zip", "Zot"}

};

std::vector<std::vector<std::string> > data_orig;

for (int i = 0; i < 3; i++) {

std::vector<std::string> row;

for (int j = 0; j < 3; j++)

row.push_back(data_array[i][j]);

data_orig.push_back(row);

}

print_matrix(data_orig);

std::vector<std::vector<std::string> > data = data_orig;

sort_table(data);

print_matrix(data);

data = data_orig;

sort_table(data, 2);

print_matrix(data);

data = data_orig;

sort_table(data, 1);

print_matrix(data);

data = data_orig;

sort_table(data, 1, true);

print_matrix(data);

data = data_orig;

sort_table(data, 0, false, desc_len_comparator);

print_matrix(data);

return 0;

}</lang>