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buggy highest element program - help needed

DragonOsman (715)
It's intentionally buggy in the book. I need to fix it. But there's also another problem for me.

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// Osman Zakir
// 11 / 10 / 2017
// Bjarne Stroustrup: Programming: Principles and Practice Using C++ 2nd Edition
// Chapter 20 "Find highest element" example code (with templated high() function)
// This program has a serious bug that I have to find and fix.

#include "../../cust_std_lib_facilities.h"
#include <iostream>
#include <vector>
#include <vld.h>

template<typename Iterator>
Iterator high(Iterator first, Iterator last);
double *get_from_jack(int *count);
std::vector<double> *get_from_jill();
void fct();

int main()
{
	fct();
	keep_window_open();
}

template<typename Iterator>
Iterator high(Iterator first, Iterator last)
	// return an iterator to the element in [first:last) that has the highest value
{
	Iterator high = first;
	for (Iterator p = first; p != last; ++p)
	{
		if (*high < *p)
		{
			high = p;
		}
	}
	return high;
}

double *get_from_jack(int *count)
{
	*count = 10;
	double *data_arr = nullptr;
	try
	{
		data_arr = new double[*count];
	}
	catch (const std::bad_alloc &e)
	{
		std::cout << "Bad allocation error: " << e.what() << '\n';
	}
	catch (const std::exception &e)
	{
		std::cout << "Exception: " << e.what() << '\n';
	}

	std::size_t i = 0;
	std::cout << "Please enter 10 velocitices or more velocities: enter anything that is not a number to stop:\n";
	for (double val; std::cin >> val;)
	{
		std::cin.ignore(32767, '\n');
		if (i >= static_cast<std::size_t>(*count))
		{
			double *new_arr = nullptr;
			try
			{
				new_arr = new double[*count + 1];
			}
			catch (const std::bad_alloc &e)
			{
				std::cout << "Bad allocation error: " << e.what() << '\n';
			}
			catch (const std::exception &e)
			{
				std::cout << "Exception: " << e.what() << '\n';
			}
			try
			{
				std::copy(data_arr, data_arr + *count, new_arr);
			}
			catch (const std::exception &e)
			{
				std::cerr << "Exception: " << e.what() << '\n';
			}
			data_arr = new_arr;
			delete[] new_arr;
			new_arr = nullptr;
		}
		data_arr[i] = val;
		++i;
	}
	std::cin.ignore(32767, '\n');
	std::cin.clear();
	std::cin.clear();
	*count = i;
	return data_arr;
}

std::vector<double> *get_from_jill()
{
	constexpr int size = 10;
	std::vector<double> *data_vec = nullptr;
	try
	{
		data_vec = new std::vector<double>(size);
	}
	catch (const std::bad_alloc &e)
	{
		std::cerr << "Bad alloction error: " << e.what() << '\n';
	}

	std::cout << "Please enter 10 velocitices or more velocities: enter anything that is not a number to stop:\n";
	for (double val; std::cin >> val;)
	{
		std::cin.ignore(32767, '\n');
		data_vec->push_back(val);
	}
	return data_vec;
}

void fct()
{
	int jack_count = 0;
	double *jack_data = get_from_jack(&jack_count);
	std::vector<double> *jill_data = get_from_jill();

	double *jack_high = high(jack_data, jack_data + jack_count);
	std::vector<double> &v = *jill_data;
	double *jill_high = high(&v[0], &v[0] + v.size());

	std::cout << "Jill's high " << *jill_high << "; Jack's high " << *jack_high << '\n';

        delete[] jack_data;
	jack_data = nullptr;
	delete jill_data;
	jill_data = nullptr;
}


The read loop for the vector won't run. And the program is giving wrong results with input like this:
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, saying that the largest value is whatever I entered last. And sometimes it gives me a heap corruption error, too. And it even freezes after printing the results, sometimes.

fct() and high() were given in the book. I wrote main() and the functions for getting the data myself.

I think I know why the program gives wrong results: It depends on what the first number is. It expects the given sequence to be sorted, and gives wrong results otherwise.

Edit: The reason it freezes is because there's a breakpoint triggered by fct() line 141. It shows there's a problem with me calling delete[] there when I run the code in the debugger. But when I comment that line out, VLD shows I have a leak because I didn't free that memory. How do I fix this? (But yeah, I need to fix the problem with get_from_jill() first, for why the input loop won't run).

Edit2: Line 141 on my IDE and line 132 on here, for some reason.
Last edited on
DragonOsman (715)
Okay, never mind about the line number; my own updated code got longer. I'll post it here:
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// Osman Zakir
// 11 / 10 / 2017
// Bjarne Stroustrup: Programming: Principles and Practice Using C++ 2nd Edition
// Chapter 20 "Find highest element" example code (with templated high() function)
// This program has a serious bug that I have to find and fix.

#include "../../cust_std_lib_facilities.h"
#include <iostream>
#include <vector>
#include <vld.h>

template<typename Iterator>
Iterator high(Iterator first, Iterator last);
double *get_from_jack(int *count);
std::vector<double> *get_from_jill();
void fct();

int main()
{
	try
	{
		fct();
		std::cin.ignore(32767, '\n');
		std::cin.clear();
	}
	catch (const std::exception &e)
	{
		std::cerr << "Exception: " << e.what() << '\n';
	}
	keep_window_open();
}

template<typename Iterator>
Iterator high(Iterator first, Iterator last)
	// return an iterator to the element in [first:last) that has the highest value
{
	Iterator high = first;
	for (Iterator p = first; p != last; ++p)
	{
		if (*high < *p)
		{
			high = p;
		}
	}
	return high;
}

double *get_from_jack(int *count)
{
	*count = 10;
	double *data_arr = nullptr;
	try
	{
		data_arr = new double[*count];
	}
	catch (const std::bad_alloc &e)
	{
		std::cout << "Bad allocation error: " << e.what() << '\n';
	}
	catch (const std::exception &e)
	{
		std::cout << "Exception: " << e.what() << '\n';
	}

	std::size_t i = 0;
	std::cout << "Please enter 10 velocitices or more velocities: enter anything that is not a number to stop:\n";
	for (double val; std::cin >> val;)
	{
		std::cin.ignore(32767, '\n');
		if (i >= static_cast<std::size_t>(*count))
		{
			double *new_arr = nullptr;
			try
			{
				new_arr = new double[*count + 1];
			}
			catch (const std::bad_alloc &e)
			{
				std::cout << "Bad allocation error: " << e.what() << '\n';
			}
			catch (const std::exception &e)
			{
				std::cout << "Exception: " << e.what() << '\n';
			}
			try
			{
				std::copy(data_arr, data_arr + *count, new_arr);
			}
			catch (const std::exception &e)
			{
				std::cerr << "Exception: " << e.what() << '\n';
			}
			data_arr = new_arr;
			delete[] new_arr;
			new_arr = nullptr;
		}
		data_arr[i] = val;
		++i;
	}
	std::cin.ignore(32767, '\n');
	std::cin.clear();
	std::cin.clear();
	*count = i;
	return data_arr;
}

std::vector<double> *get_from_jill()
{
	constexpr int size = 10;
	std::vector<double> *data_vec = nullptr;
	try
	{
		data_vec = new std::vector<double>(size);
	}
	catch (const std::bad_alloc &e)
	{
		std::cerr << "Bad alloction error: " << e.what() << '\n';
	}

	std::cout << "Please enter 10 velocitices or more velocities: enter anything that is not a number to stop:\n";
	double val = 0;
	while (std::cin >> val)
	{
		data_vec->push_back(val);
	}
	return data_vec;
}

void fct()
{
	int jack_count = 0;
	double *jack_data = get_from_jack(&jack_count);
	std::vector<double> *jill_data = get_from_jill();

	double *jack_high = high(jack_data, jack_data + jack_count);
	std::vector<double> &v = *jill_data;
	double *jill_high = high(&v[0], &v[0] + v.size());

	std::cout << "Jill's high " << *jill_high << "; Jack's high " << *jack_high << '\n';

        delete[] jack_data;
	jack_data = nullptr;
	delete jill_data;
	jill_data = nullptr;
}
Last edited on
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