I am making a simple encryption program, but I can't get the return function right. I want to replace the [ with \n. But I can't get this to work. This is my current solution:
#include <string>
#include <iostream>
#include <algorithm>
#include <fstream>
std::ifstream in("file.txt");
std::ofstream out("result.txt");
std::string line;
while (!in.eof())
{
std::getline(in, line);
std::replace(line.begin(), line.end(), "[", "\n");
out << line;
}
Replace " with '
This means you have to use character instead of string.
This is working at my side.
#Blaze
Related
I want to be able to a string that contains certain characters in a file that contains one string per line.
#include <iostream>
#include <fstream>
#include <string>
int main(){
string line;
ifstream infile;
infile.open("words.txt");
while(getline(infile, line,' ')){
if(line.find('z')){
cout << line;
}
}
}
That's my attempt at finding all the string that contains the character z.
The text file contains random strings such as
fhwaofhz
cbnooeht
rhowhrj
perwqreh
dsladsap
zpuaszu
so with my implementation, it should only print out the strings with the character z in it. However, it seems to be reprinting out all the contents from the text file again.
Problem:
In your file the strings aren't separated by a space (' ') which is the end delimiter, they are separated by a end of line ('\n'), that is a different character. As a consequence, in the first getline everything goes to line. line contains all the text in the file, including z's, so all the content is printed. Finally, the code exits the while block after running once because getline reaches the end of the file and fails.
If you run this code
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::string line;
std::ifstream infile;
infile.open("words.txt");
while(getline(infile, line,' ')){
std::cout << "Hi";
if(line.find('z')){
std::cout << line;
}
}
}
"Hi" will be only printed once. That is because the while block is only executed once.
Additionaly, see that line.find('z') won't return 0 if not match is found, it will return npos. See it running this code (As it says here):
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::string line;
std::ifstream infile;
infile.open("words.txt");
while(getline(infile,line)){
std::cout << line.find('z');
if(line.find('z')){
std::cout << line << "\n";
}
}
}
Solution:
Use getline(infile,line) that is more suitable for this case and replace if(line.find('z')) with if(line.find('z') != line.npos).
while(getline(infile,line)){
if(line.find('z') != line.npos){
std::cout << line << "\n";
}
}
If you need to put more than one string per line you can use the operator >> of ifstream.
Additional information:
Note that the code you posted won't compile because string, cout and ifstream are in the namespace std. Probably it was a part of a longer file where you were using using namespace std;. If that is the case, consider that it is a bad practice (More info here).
Full code:
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::string line;
std::ifstream infile;
infile.open("words.txt");
while(getline(infile,line)){
if(line.find('z') != line.npos){
std::cout << line << "\n";
}
}
}
getline extracts characters from the source and stores them into the variable line until the delimitation character is found. Your delimiter character is a space (" "), which isn't present in the file, so line will contain the whole file.
Try getline(infile, line, '\n') or simply getline(infile, line) instead.
The method find returns the index of the found character, where 0 is a perfectly valid index. If the character is not found, it returns npos. This is a special value whcih indicates "not found", and it's nonzero to allow 0 to refer to a valid index. So the correct check is:
if (line.find('z') != string::npos)
{
// found
}
I have a large .txt file and I want to read all of the words inside it and print them on the screen. The first thing I did was to use std::getline() in this way:
std::vector<std::string> words;
std::string line;
while(std::getline(std::cin,line)){
words.push_back(line);
}
and then I printed out all the words present in the vector words. The .txt file is passed from command line as ./a.out < myTxt.txt.
The problem is that each component of the vector is a whole line, and so I am not reading each word.
The problem, I guess, is the spaces between words: how can I tell the code to ignore them? More specifically, is there any function that I can use in order to read each word from a .txt file?
UPDATE:
I'm trying to avoid all the commas ., but also ? ! (). I used find_first_of(), but my program doesn't work. Also, I don't know how to set what are the characters I don't want to be read, i.e. ., ?, !, and so on
std::vector<std::string> my_vec;
std::string line;
while(std::cin>>line){
std::size_t pos = line.find_first_of("!");
std::string line = line.substr(pos);
my_vec.push_back(line);
}
'>>' operator of type string exactly fills your requirements.
std::vector<std::string> words;
std::string line;
while (std::cin >> line) {
words.push_back(line);
}
If you need remove some noisy characters, e.g. ',','.', you can replace them with space character first.
#include <iostream>
#include <sstream>
#include <vector>
#include <algorithm>
int main() {
std::vector<std::string> words;
std::string line;
while (getline(std::cin, line)) {
std::transform(line.begin(), line.end(), line.begin(),
[](char c) { return std::isalnum(c) ? c : ' '; });
std::stringstream linestream(line);
std::string w;
while (linestream >> w) {
std::cout << w << "\n";
words.push_back(w);
}
}
}
cppreference
The getline function, as it sounds, only returns a whole line. You can split each line on spaces after reading it, or you can read word by word using operator>>:
string word;
while (cin >> word){
cout << word << "\n";
words.push_back(word);
}
Use operator>> instead of std::getline(). The operator will read individual whitespace-separated substrings for you.
#include <iostream>
#include <string>
#include <vector>
std::vector<std::string> my_vec;
std::string s;
while (std::cin >> s){
// use s as needed...
}
However, you may still end up receiving strings that have punctuation in them without any surrounding whitespace, ie hello,world, so you will have to manually split those strings as needed, eg:
#include <iostream>
#include <string>
#include <vector>
#include <cctype>
std::vector<std::string> my_vec;
std::string s;
while (std::cin >> s){
std::string::size_type start = 0, pos;
while ((pos = s.find_first_of(".,?!()", start)) != std::string::npos){
my_vec.push_back(s.substr(start, pos-start));
start = s.find_first_not_of(".,?!() \t\f\r\n\v", pos+1);
}
if (start == 0)
my_vec.push_back(s);
else if (start != std::string::npos)
my_vec.push_back(s.substr(start));
}
What is the right way to split a string like below at a specific character-combination into a string vector?
string myString = "This is \n a test. Let's go on. \n Yeah.";
split at "\n" to get this result:
vector<string> myVector = {
"This is ",
" a test. Let's go on. ",
" Yeah."
}
I was using boost algorithm library but now I'd like to achieve this all without using an external library like boost.
#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>
std::vector<std::string> result;
boost::split(result, "This is \n a test. Let's go on. \n Yeah.",
boost::is_any_of("\n"), boost::token_compress_on);
How about something like this:
#include <iostream>
#include <sstream>
#include <vector>
#include <string>
#include <iterator>
class line : public std::string {};
std::istream &operator>>(std::istream &iss, line &line)
{
std::getline(iss, line, '\n');
return iss;
}
int main()
{
std::istringstream iss("This is \n a test. Let's go on. \n Yeah.");
std::vector<std::string> v(std::istream_iterator<line>{iss}, std::istream_iterator<line>{});
// test
for (auto const &s : v)
std::cout << s << std::endl;
return 0;
}
Basically make a new type of string which is line and use stream iterator to read whole lines straight to vector range constructor
Working demo: https://ideone.com/4qdfY2
Solution 1: Just to remove "\n" from the string.
Just to remove "\n", you can use erase-remove idiom . SEE LIVE HERE
#include <iostream>
#include <string>
#include <algorithm>
int main()
{
std::string myString = "This is \n a test. Let's go on. \n Yeah.";
myString.erase(std::remove(myString.begin(), myString.end(), '\n'),
myString.end());
std::cout << myString<< std::endl;
}
Output:
This is a test. Let's go on. Yeah
Solution 2: To remove "\n" from the string and save each split at \n to a vector. (un-efficient)
Replace all \n occurance with some other charectors, which doesn't exist in the string (here I have chosen ;). Then parse with the help of std::stringstream and std::getline as follows. SEE LIVE HERE
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <sstream>
int main()
{
std::string myString = "This is \n a test. Let's go on. \n Yeah.";
std::replace(myString.begin(), myString.end(), '\n', ';');
std::stringstream ssMyString(myString);
std::string each_split;
std::vector<std::string> vec;
while(std::getline(ssMyString, each_split, ';')) vec.emplace_back(each_split);
for(const auto& it: vec) std::cout << it << "\n";
}
Output:
This is
a test. Let's go on.
Yeah.
Solution 3: To remove "\n" from the string and save each split at \n to a vector.
Loop through the string and find positions(using std::string::find) where \n(end position) finds. Push back the substrings (std::string::substr) using the information of starting position and the number of charectors between start and end position. Each time update the start and end positions, so that look up will not start again from the beging of the input string. SEE LIVE HERE
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstddef>
int main()
{
std::string myString = "This is \n a test. Let's go on. \n Yeah.";
std::vector<std::string> vec;
std::size_t start_pos = 0;
std::size_t end_pos = 0;
while ((end_pos = myString.find("\n", end_pos)) != std::string::npos)
{
vec.emplace_back(myString.substr(start_pos, end_pos - start_pos));
start_pos = end_pos + 1;
end_pos += 2;
}
vec.emplace_back(myString.substr(start_pos, myString.size() - start_pos)); // last substring
for(const auto& it: vec) std::cout << it << "\n";
}
Output:
This is
a test. Let's go on.
Yeah.
I am working on creating a program that is supposed to read a text file (ex. dog, buddy,,125,,,cat,,,etc...) line by line and parse it based on commas. This is what I have so far but when I run it, nothing happens. I am not entirely sure what i'm doing wrong and I am fairly new to the higher level concepts.
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <cstdlib>
#include <sstream>
#include <vector>
using namespace std;
int main()
{
std::ifstream file_("file.txt"); //open file
std::string line_; //declare line_ as a string
std::stringstream ss(line_); //using line as stringstream
vector<string> result; //declaring vector result
while (file_.is_open() && ss.good())
{ //while the file is open and stringstream is good
std::string substr; //declares substr as a string
getline( ss, substr, ',' ); //getting the stringstream line_ and substr and parsing
result.push_back(substr);
}
return 0;
}
Did you forget to add a line like std::getline(file_, line_);? file_ was not read from at all and line_ was put into ss right after it was declared when it was empty.
I'm not sure why you checked if file_ is open in your loop condition since it will always be open unless you close it.
As far as I know, using good() as a loop condition is not a good idea. The flags will only be set the first time an attempt is made to read past the end of the file (it won't be set if you read to exactly the end of the file when hitting the delimiter), so if there was a comma at the end of the file the loop will run one extra time. Instead, you should somehow put the flag check after the extraction and before you use the result of the extraction. A simple way is to just use the getline() call as your loop condition since the function returns the stream itself, which when cast into a bool is equivalent to !ss.fail(). That way, the loop will not execute if the end of the file is reached without extracting any characters.
By the way, comments like //declaring vector result is pretty much useless since it gives no useful information that you can't easily see from the code.
My code:
#include <iostream>
#include <fstream>
#include <vector>
#include <sstream>
int main()
{
std::ifstream file("input.txt");
std::string line, word;
std::vector<std::vector<string>> result; //result[i][j] = the jth word in the input of the ith line
while(std::getline(file, line))
{
std::stringstream ss(line);
result.emplace_back();
while(std::getline(ss, word, ','))
{
result.back().push_back(word);
}
}
//printing results
for(auto &i : result)
{
for(auto &j : i)
{
std::cout << j << ' ';
}
std::cout << '\n';
}
}
I'm trying to split a string in individual words using vector in C++. So I would like to know how to ignore spaces in vector, if user put more than one space between words in string.
How would I do that?
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
cout<<"Sentence: ";
string sentence;
getline(cin,sentence);
vector<string> my;
int start=0;
unsigned int end=sentence.size();
unsigned int temp=0;
while(temp<end){
int te=sentence.find(" ",start);
temp=te;
my.push_back(sentence.substr(start, temp-start));
start=temp+1;
}
unsigned int i;
for(i=0 ; i<my.size() ; i++){
cout<<my[i]<<endl;
}
return 0;
}
Four things:
When reading input from a stream into astring using the overloaded >> operator, then it automatically separates on white-space. I.e. it reads "words".
There exists an input stream that uses a string as the input, std::istringstream.
You can use iterators with streams, like e.g. std::istream_iterator.
std::vector have a constructor taking a pair of iterators.
That means your code could simply be
std::string line;
std::getline(std::cin, line);
std::istringstream istr(line);
std::vector<std::string> words(std::istream_iterator<std::string>(istr),
std::istream_iterator<std::string>());
After this, the vector words will contain all the "words" from the input line.
You can easily print the "words" using std::ostream_iterator and std::copy:
std::copy(begin(words), end(words),
std::ostream_iterator<std::string>(std::cout, "\n"));
The easiest way is to use a std::istringstream like follows:
std::string sentence;
std::getline(std::cin,sentence);
std::istringstream iss(sentence);
std::vector<std::string> my;
std::string word;
while(iss >> word) {
my.push_back(word);
}
Any whitespaces will be ignored and skipped automatically.
You can create the vector directly using the std::istream_iterator which skips white spaces:
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <iterator>
int main() {
std::string str = "Hello World Lorem Ipsum The Quick Brown Fox";
std::istringstream iss(str);
std::vector<std::string> vec {std::istream_iterator<std::string>(iss),
std::istream_iterator<std::string>() };
for (const auto& el : vec) {
std::cout << el << '\n';
}
}
Here is a function which divides given sentence into words.
#include <string>
#include <vector>
#include <sstream>
#include <utility>
std::vector<std::string> divideSentence(const std::string& sentence) {
std::stringstream stream(sentence);
std::vector<std::string> words;
std::string word;
while(stream >> word) {
words.push_back(std::move(word));
}
return words;
}
Reducing double, triple etc. spaces in string is a problem you'll encounter again and again. I've always used the following very simple algorithm:
Pseudocode:
while " " in string:
string.replace(" ", " ")
After the while loop, you know your string only has single spaces since multiple consecutive spaces were compressed to singles.
Most languages allow you to search for a substring in a string and most languages have the ability to run string.replace() so it's a useful trick.