PPP2 Chapter 11 Exercise 13

[DragonOsman]

Okay, here's another one. Reading a text file and then writing out the words in reverse order. I'm having trouble printing out the words in reverse order. How do I read strings from a file in reverse order them in a vector? Maybe that'll help.

Anyway, this is what I have right now (I've included the Exercise Specs in comments at the top of the file, as always):

// chapter11ex13.cpp : Defines the entry point for the console application.
// Osman Zakir
// 3 / 9 / 2017
// Bjarne Stroustrup: Programming: Principles and Practice Using C++ 2nd Edition
// Chapter 11 Exercise 13
// Exercise Specifications:
/**
 * Reverse the order of words (defined as whitespace-separated strings) in a
 * file. For example, Norwegian Blue parrot becomes parrot Blue Norwegian .
 * You are allowed to assume that all the strings from the file will fit into
 * memory at once.
 */

#include "../../cust_std_lib_facilities.h"
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>

int main()
{
	using namespace std;
	cout << "Please enter name of input file: ";
	string ifname;
	cin >> ifname;
	ifstream ifs{ ifname };
	if (!ifs)
	{
		cout << "Error: cannot open input file " << ifname << '\n';
		keep_window_open();
		return 1;
	}

	string file_input;
	vector<string> input_vector;
	while (getline(ifs, file_input))
	{
		input_vector.push_back(file_input);
		reverse(input_vector.begin(), input_vector.end());
	}

	for (auto i = input_vector.rbegin(); i != input_vector.rend(); ++i)
	{
		
		cout << *i;
	}
	cout << '\n';
	keep_window_open();
}

Right now, the input file's contents are printed out as is.

[ne555]

draw the flow diagram, let's start from there.


> Reverse the order of words (defined as whitespace-separated strings)
¿where are you getting each word?

[gunnerfunner]

you're reading the whole line but you need to read it in word by word so that you can reverse it later on. so stringstream the line, stream >> temp_string (which parses on whitespace), push_back(temp_string) into std::vector<std::string> and then apply the reverse iterators to print

[DragonOsman]

@gunnerfunner: Great advice, thanks. I'll see if I can do that without asking for further help (I'll try to finish it myself, but if I can't, I'll try asking again).

So basically I need to define an istringstream and read words with it one by one in a loop, and then push them back into the vector?

@me555: I have an input file. It's a really short file, though:

The Norwegian Blue parrot is a parrot that, obviously, would be from Norway if it existed.

Edit: Okay, I did it without istrinstream since I didn't get how to do that while also actually reading from the input file I want to read from. This is my current code (and it works perfectly as far as I can see):

// chapter11ex13.cpp : Defines the entry point for the console application.
// Osman Zakir
// 3 / 9 / 2017
// Bjarne Stroustrup: Programming: Principles and Practice Using C++ 2nd Edition
// Chapter 11 Exercise 13
// Exercise Specifications:
/**
 * Reverse the order of words (defined as whitespace-separated strings) in a
 * file. For example, Norwegian Blue parrot becomes parrot Blue Norwegian .
 * You are allowed to assume that all the strings from the file will fit into
 * memory at once.
 */

#include "../../cust_std_lib_facilities.h"
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>

std::vector<std::string> fill_v(std::istream &is);
void print_strings_v(const std::vector<std::string> &str_v);

int main()
{
	using namespace std;
	cout << "Please enter name of input file: ";
	string ifname;
	cin >> ifname;
	ifstream ifs{ ifname };
	if (!ifs)
	{
		cout << "Error: cannot open input file " << ifname << '\n';
		keep_window_open();
		return 1;
	}
	vector<string> input_v = fill_v(ifs);
	print_strings_v(input_v);
	keep_window_open();
}

std::vector<std::string> fill_v(std::istream &is)
{
	using namespace std;
	string input;
	vector<string> input_v;
	while (is >> input)
	{
		input_v.push_back(input);
	}
	return input_v;
}

void print_strings_v(const std::vector<std::string> &str_v)
{
	using namespace std;
	for (auto i = str_v.rbegin(); i != str_v.rend(); ++i)
	{
		cout << *i << ' ';
	}
	cout << '\n';
}

Anyone have a long input file I can test this baby out on?

[48T7M4Gy]

Anyone have a long input file I can test this baby out on?

Why not just find a suitable amount on an online newspaper and cut and paste into a .txt file.

[Thomas1965]

Maybe try an ebook at Gutenberg.org

[gunnerfunner]

to avoid reallocation of the vector during read what's the best way to reserve vector memory at the outset, depending on the file size?
the example here http://www.cplusplus.com/reference/istream/istream/tellg/ suggests a char array depending on the file size but how'd that translate to std::vector<std::string> as we're using in this case?

[DragonOsman]

How would I specify the size of a vector beforehand?

[gunnerfunner]

How would I specify the size of a vector beforehand?

this is quite easily done but the question I raised was how to get this size before-hand:

#include <iostream>
#include <vector>
#include <string>

int main()
{
    std::vector<std::string> myVec(1000);
    std::cout << myVec.size()<<"\n";
}

[gunnerfunner]

Actually Dragon it might be better to use the reserve() method just to allocate memory to prevent future reallocations. Giving an initial size to the vector means any subsequent push_back or emplace_back would start from the end of the sized vector:

#include <iostream>
#include <vector>
#include <string>

int main()
{
    std::vector<std::string> myVec{};
    myVec.reserve(1000);
    std::cout << myVec.size()<<"\n";//prints 0
}

[DragonOsman]

So, like this?

// chapter11ex13.cpp : Defines the entry point for the console application.
// Osman Zakir
// 3 / 9 / 2017
// Bjarne Stroustrup: Programming: Principles and Practice Using C++ 2nd Edition
// Chapter 11 Exercise 13
// Exercise Specifications:
/**
 * Reverse the order of words (defined as whitespace-separated strings) in a
 * file. For example, Norwegian Blue parrot becomes parrot Blue Norwegian .
 * You are allowed to assume that all the strings from the file will fit into
 * memory at once.
 */

#include "../../cust_std_lib_facilities.h"
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>

std::vector<std::string> fill_v(std::istream &is);
void print_strings_v(const std::vector<std::string> &str_v);

int main()
{
	using namespace std;
	cout << "Please enter name of input file: ";
	string ifname;
	cin >> ifname;
	ifstream ifs{ ifname };
	if (!ifs)
	{
		cout << "Error: cannot open input file " << ifname << '\n';
		keep_window_open();
		return 1;
	}
	ifs.seekg(0, ifs.end);
	size_t length = ifs.tellg();
	ifs.seekg(0, ifs.beg);
	vector<string> input_v;
	input_v.reserve(length);
	input_v = fill_v(ifs);
	print_strings_v(input_v);
	keep_window_open();
}

std::vector<std::string> fill_v(std::istream &is)
{
	using namespace std;
	string input;
	vector<string> input_v;
	while (is >> input)
	{
		input_v.push_back(input);
	}
	return input_v;
}

void print_strings_v(const std::vector<std::string> &str_v)
{
	using namespace std;
	for (auto i = str_v.rbegin(); i != str_v.rend(); ++i)
	{
		cout << *i << ' ';
	}
	cout << '\n';
}

By the way, how much of a chance do you guys think there is for the Networking TS to be standardized? I really want it to happen, but I can't go and participate in committee meetings (I probably shouldn't even if I could, though, since I'm still learning).

[gunnerfunner]

size_t length = ifs.tellg();

tellg() return type is std::streampos http://www.cplusplus.com/reference/ostream/ostream/tellp/

You should be able to convert the result from tellp to a std::string::size_type by casting.

http://stackoverflow.com/questions/5262027/how-do-all-the-different-size-types-relate-to-each-other
tellp() has the same return type as tellg() http://www.cplusplus.com/reference/ostream/ostream/tellp/ which means that the solution offered through above link should also be applicable here
in turn, you could 'optimize' this a bit further by making a reasonable assumping about the average length of words - say its 4 - therefore input_v.reserve would be scaled down by a factor of 4 from static_cast<std::string::size_type>(length)
and this link is also very useful for reading really large files beyond the size of your RAM:
http://stackoverflow.com/questions/34751873/how-to-read-huge-file-in-c
ps: i must also add the disclaimer that i've not had to read in very large files, so if anybody has a better/different suggestion do chip in

[DragonOsman]

Yeah, thanks for those.

I'll read up on those later. But for now I think I can mark this as "solved".

@gunnerfunner: You think you could come over to the thread I made for Chapter 12 Exercise 11 (it's the one that mentions equilateral triangles in the title)? I have a runtime error about two polygons lying in a straight line, and apparently my y-axis values are all outside the window. I don't know how to best points in a GUI, I guess.

[gunnerfunner]

You think you could come over to the thread I made for Chapter 12 Exercise 11

thanks for the invite but I'd be utterly useless at GUI stuff and need to learn myself, good luck!