Making reversed output using vector, stl - c++

Question

I read data from a text file named test.txt. File contents:
C++ is disturbing me every day
and i want a result like,
++C si gnibrutsid yreve yad (reversed words)
is me C++ day every disturbing (sorted based on length)
How can I do it? Here's what I have tried:
#include <fstream>
#include <iostream>
#include <vector>
using namesapce std;
string file { "test.txt" }
int main()
{
ifstream in(file);
vector<char> v{istreambuc_iterator<char>(in), istreambuf_iterator < char()};
/* my horrible coding
int n{ 0 };
for (auto i = v.cbegin(); i < v.cend(); ++i)
{
int tmp=0;
if (*i == ' ')
{
v[n] = tmp;
v[n] = *i;
tmp = *i;
}n++;
}
--------------------*/
for (auto c : v) cout << c;
}

Answer 1

Read each word individually, and then do whatever processing you want:
#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <vector>
void printReversedWords(std::vector<std::string> const& vec) noexcept {
for (auto const& str : vec) {
std::copy(str.crbegin(), str.crend(),
std::ostream_iterator<char>(std::cout));
std::cout << ' ';
}
std::cout << '\n';
}
// remove noexcept if you care catching bad_alloc
void printSortedVec(std::vector<std::string> const& vec) noexcept {
auto const vec_view = [&vec] {
std::vector<std::string const*> vec_view;
vec_view.reserve(vec.size());
std::transform(vec.cbegin(), vec.cend(), std::back_inserter(vec_view),
[](auto const& str) { return &str; });
std::sort(vec_view.begin(), vec_view.end(),
[](auto const* const pstr1, auto const* const pstr2) {
return pstr1->size() < pstr2->size();
});
return vec_view;
}(); // IILE
for (auto const* const pstr : vec_view) std::cout << *pstr << ' ';
std::cout << '\n';
}
int main() {
auto constexpr fileName = "./test.txt";
std::ifstream in(fileName);
if (!in) {
std::cerr << "Failed to open the file";
return -1;
}
std::vector<std::string> const vec{ std::istream_iterator<std::string>(in), {} };
printReversedWords(vec);
printSortedVec(vec);
}

Answer 2

You can use C++ build in algorithms.
First see the example code, which could give you and idea on how it could be implemented:
#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include <iterator>
#include <algorithm>
const std::string fileName{ "test.txt" };
int main() {
// Open the file and check, if it could be opened.
if (std::ifstream inStream(fileName); inStream) {
// Read all words from the file into our vector
std::vector words(std::istream_iterator<std::string>(inStream), {});
std::cout << "\nReversed words:\n\n";
// Show reversed words
std::transform(words.begin(), words.end(), std::ostream_iterator<std::string>(std::cout, " "),
[](const std::string& s) { return std::string(s.rbegin(), s.rend()); });
// Sort
std::sort(words.begin(), words.end());
// Show sorted list of words
std::cout << "\n\n\nSorted list of words:\n\n";
std::copy(words.begin(), words.end(), std::ostream_iterator<std::string>(std::cout, " "));
std::cout << "\n\n";
}
else {
std::cerr << "\n*** Error: Could not open file: " << fileName << "\n\n";
}
return 0;
}
First, we open the file and check, if open was successful. This we do with the if with init statement. So we prevent pollution of the outer namespace. The stream variable is just used within the if-statement. And by using the init part of the if-statement, we will open the file. The condition part of the if-statement is just the stream variable. And this will work, because the bool operator of the ios::stream is overloaded and will return, if the file stream is ok or not.
OK, now the file is open, and we wan to read all words. So, we define a std::vector named "words". There is no need to define the template parameter of the std::vector. With C++17 CTAD (Class Template Argument Deduction), because it will be deduced automatically.
We use the range constructor of the std::vector (here number 5). The begin iterator is the std::istream_iterator. It will call the extractor operator >> until all input is consumed. Please note. We do not need to explicitly mention the end iterator, since the {} will be used as default initializer. Please see here: constructor number 1.
So, be defining the variable and using its range constructor, we will read all words from the file.
For reversing the words, we will also use the range constructor of the std::sting. And as begin and end iterator we use the reversed versions. So, very simple.
And to show the reversed strings, we will use std::transform, go over all words, put it into the std::ostream_operator. This will call the inserter operator << for all words. And the transformation function is a Lambda, that returns the reversed string.
Sorting is trivial and also copying the sorted words to std::cout is rather simple.
All this results in elegant and modern C++ code, with only a few lines.