I'm obviously not quite getting the 'end-of-file' concept with C++ as the below program just isn't getting past the "while (cin >> x)" step. Whenever I run it from the command line it just sits there mocking me.
Searching through SO and other places gives a lot of mention to hitting ctrl-z then hitting enter to put through an end-of-file character on windows, but that doesn't seem to be working for me. That makes me assume my problem is elsewhere. Maybe defining x as a string is my mistake? Any suggestions about where I'm going wrong here would be great.
Note: sorry for the lack of comments in the code - the program itself is supposed to take in a series of
words and then spit back out the count for each word.
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>
using std::cin;
using std::cout; using std::endl;
using std::sort;
using std::string; using std::vector;
int main()
{
cout << "Enter a series of words separated by spaces, "
"followed by end-of-file: ";
vector<string> wordList;
string x;
while (cin >> x)
wordList.push_back(x);
typedef vector<string>::size_type vec_sz;
vec_sz size = wordList.size();
if (size == 0) {
cout << endl << "This list appears empty. "
"Please try again." << endl;
return 1;
}
sort(wordList.begin(), wordList.end());
cout << "Your word count is as follows:" << endl;
int wordCount = 1;
for (int i = 0; i != size; i++) {
if (wordList[i] == wordList[i+1]) {
wordCount++;
}
else {
cout << wordList[i] << " " << wordCount << endl;
wordCount = 1;
}
}
return 0;
}
If you're on windows ^Z has to come as the first character after a newline, if you're on a unixy shell then you want to type ^D.
The input portion of your code works. The only real problem I see is with the loop the tries to count up the words:
for (int i = 0; i != size; i++) {
if (wordList[i] == wordList[i+1]) {
The valid subscripts for wordList run from 0 through size-1. In the last iteration of your loop, i=size-1, but then you try to use wordList[i+1], indexing beyond the end of the vector and getting undefined results. If you used wordList.at(i+1) instead, it would throw an exception, quickly telling you more about the problem.
My guess is that what's happening is that you're hitting Control-Z, and it's exiting the input loop, but crashing when it tries to count the words, so when you fix that things will work better in general. If you really can't get past the input loop after fixing the other problem(s?), and you're running under Windows, you might try using F6 instead of entering control-Z -- it seems to be a bit more dependable.
I pretty much always use getline when using cin (particularly when what I want is a string):
istream& std::getline( istream& is, string& s );
So, you'd call getline(cin, x) and it would grab everything up to the newline. You have to wait for the newline for cin to give you anything anyway. So, in that case, your loop would become:
while(getline(cin, x))
wordList.push_back(x);
cin does not accept blank space or line breaks so execution of cin does not complete unless you enter something , here is a test program that gives you what you want
#include "stdafx.h"
#include<iostream>
#include <string>
#include <sstream>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string str = "";
while(std::getline(cin, str) && str!="")
{
cout<<"got "<<str<<endl;
}
cout<<"out"<<endl;
cin>>str;
return 0;
}
Related
I've tried a bunch of methods listed on here but none of them work. It's always waiting for more input.
I've tried while(std::getline(std::cin, line)) and the method below, nothing seems to work:
#include <iostream>
#include <sstream>
using namespace std;
int main(){
long length = 1UL<<32;
int array[length];
// memset(array, 0, (length-1) * sizeof(int));
for(int i = 0; i < length; i++)
array[i] = 0;
string line;
int num;
while(!cin.eof()){
getline(cin,line);
stringstream ss(line);
ss >>num;
array[num]++;
}
for(int i = 0; i < length; i++)
if(array[i]){
cout << i << ": ";
cout << array[i] << endl;
}
}
First off, do not use std::cin.eof() to control your loop! It doesn't work. Also, you always need to check for successful input after the input.
That said, to terminate the input you'll need to enter the appropriate end of file character, probably at the start of the line (how it works entirely somewhat depends on the system, some settings, etc.). On Windows you'd use Ctrl-Z, on UNIXes you'd use Ctrl-D.
First off, this part of your program attempts to allocate 4 GB of memory on the stack, which doesn't work on my machine (good luck finding any machine with 4 GB of continuous memory space):
long length = 1UL<<32;
int array[length];
If I change that to a much more reasonable:
long length = 32;
Then it works fine for me:
$ g++ -g test.cpp -o test && ./test
2
5
# pressed control+d
2: 1
5: 2
$
So I'm guessing something else is wrong.
Note: Unless you actually plan to use all of those indexes, you may want to considering using an unordered_map, so you only use the space you actually need.
The condition you are looking for can be most easily tested by evaluating "std::cin" as a bool, i.e. while (cin). But it won't do this until you have tried to read beyond EOF, so expect an empty getline:
#include <iostream>
#include <string>
int main() {
std::string input;
while (std::cin) {
std::cout << "Type something in:\n";
std::getline(std::cin, input);
if(input.empty())
continue;
std::cout << "You typed [" << input << "]\n";
}
std::cout << "Our work here is done.\n";
return 0;
}
Live demo: http://ideone.com/QR9fpM
A string is a variable-length sequence of characters. Why does it receive anything and prints it out?
#include <iostream>
#include <string>
using namespace std;
int main (){
string word;
while (cin >> word){
cout << word << endl;
}
return 0;
}
In this program, we read into a string, not an int. How can I fall out of this while loop i.e hit an invalid input?
Reading into a string will not fail, all input is valid. You may add any validation you like once the string is read.
Your question is a little vague, but if you're asking how to end the loop you can do it with an end-of-file. On Linux this you can generate one from the console with Control-D, and on Windows with Control-Z plus Enter.
Because you are taking the input in a string and string is a sequence of characters .so it takes anything you input from the keyboard either it is number or alphabet or any special character .
How can I check for invalid input?
If you could define what you consider to be "invalid input" you can filter for it in one of the std::string helper methods. In your example you eluded to numbers not being strings... so if you want to do something with pure numbers...
#include <iostream>
#include <string>
using std::string;
using std::cin;
using std::cout;
using std::endl;
int main (){
string word;
while (cin >> word){
bool isNumber = (word.find_first_not_of("0123456789") == std::string::npos);
if (isNumber){
cout << "it's a number! " << word << endl;
}else{
cout << word << endl;
}
}
return 0;
}
I am trying to create an vector <int> whose size is not pre-defined. It should take in numbers as long as there are numbers in the input terminal and should stop reading when I hit Enter. I tried many solutions including the ones given here and here. In the second case, I can enter a non-integer to terminate the input to the vector. If I use the first solution (code added below), it listens to the input indefinitely.
Code:
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <iterator>
using std::cout;
using std::cin;
using std::vector;
using std::string;
using std::istringstream;
int main()
{
//cout << "Enter the elements of the array: \n";
//vector <int> arr ( std::istream_iterator<int>( std::cin ), std::istream_iterator<int>() );
vector <int> arr;
string buf;
cout << "Enter the elements of the array: \n";
while(getline(cin, buf))
{
istringstream ssin(buf);
int input;
while(ssin >> input)
{
arr.push_back(input);
}
}
cout << "The array: \n";
for(size_t i = 0; i < arr.size(); i++)
{
cout << arr[i] << " ";
}
return 0;
}
1) I don't feel that typing in a character or a very large number to end listening to input is very elegant. However, the solution with istringstream seems to be the way to go. I am not sure why it doesn't work.
2) Is there any way to detect the Enter from keyboard to terminate listening to input? I tried using cin.get(), but it changed the numbers in the vector.
3) Any other methods or suggestions?
Let's take things one step at a time.
We want to read up until enter is pressed. That means you probably want to use std:getline to read a line.
Then you want to parse it, so you want to put the line into an istringstream.
Then you want to read numbers. While you're reading them, you apparently want to ignore anything other than digits, and you want to keep reading even if you get to a group of digits that can't be converted to a number.
That leaves a few things that aren't entirely clear, such as what to do with that input that's too large to convert? Do you want to just skip to the next? Do you want to read some digits as a number, then read remaining digits as another number?
Likewise, what do you want to do if you get something like "123a456"? Should it be skipped completely, read as "123" (and the "a456" ignored)? Should it be read as "123" and "456", and just the "a" ignored?
For the moment let's assume that we're going to read space-separated groups of characters, and convert all those to numbers that we can. If something is too big to convert to a number, we'll ignore it (in its entirety). If we have a group like "123a456", we'll read the "123" as a number, and ignore the "a456".
To achieve this, we can do something like this:
std::string line;
std::getline(infile, line);
std::istringstream input(line);
std::string word;
std::vector<int> output;
while (input >> word) {
try {
int i = std::stoi(word);
output.push_back(i);
}
catch (...) {}
}
For example, given input like: "123a456 321 1111233423432434342343223344 9", this will read in [123, 321, 9].
Of course, I'm just taking a guess about your requirements, and I haven't worked at making this particularly clean or elegant--just a straightforward implementation of one possible set of requirements.
Please see the comments from #LearningC and #M.M.
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <iterator>
using std::cout;
using std::cin;
using std::vector;
using std::string;
using std::istringstream;
int main()
{
vector <int> arr;
string buf;
int input;
cout << "Enter the elements of the array: \n";
getline(cin, buf);
istringstream ssin(buf);
while(ssin >> input)
{
arr.push_back(input);
}
cout << "The array: \n";
for(size_t i = 0; i < arr.size(); i++)
{
cout << arr[i] << " ";
}
return 0;
}
I'm having difficulties with a particular piece of code I'm learning from "Programming Principles And Practice Using C++".
I can't get an output from a loop refering to a vector. Am using std_lib_facilities and stdafx because the book and MVS told me so.
#include "stdafx.h"
#include "../../std_lib_facilities.h"
int main()
{
vector<string>words;
for(string temp; cin>>temp; )
words.push_back(temp);
cout << "Number of words: " << words.size() << '\n';
}
This will produce nothing. I'll get the prompt, type in some words, then enter, then nothing.
Tried some variations I got here and from other websites as well, such as:
//here i tried the libraries the guy used in his code
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
cout << "Please enter a series of words followed by End-of-File: ";
vector<string> words;
string word;
string disliked = "Broccoli";
while (cin >> word)
words.push_back(word);
cout << "\nNumber of words: " << words.size() << endl;
// cycle through all strings in vector
for (int i = 0; i < words.size(); ++i)
{
if (words[i] != disliked)
cout << words[i] << endl;
else
cout << "BLEEP!\n";
}
return 0;
}
Still nothing.
After trying some things, by elimination I'm pretty certain the problem is with the loop-to-vector communication, because all of these work fine:
int main()
{
vector<string>words = { "hi" };
words.push_back("hello");
cout << words[1] << "\n"; // this will print hello
for (int i = 0; i < words.size();++i) {
cout << words[i] << "\n"; // this will print out all elements
// inside vector words, ( hi, hello)
}
cout << words.size();// this will print out number 2
for (string temp; cin >> temp;) {
words.push_back(temp);
}
cout << words.size();// this won't do anything after i type in some
// words; shouldn't it increase the size of the
// vector?
}
Neither will this alone:
int main()
{
vector<string>words = { "hi" };
for (string temp; cin >> temp;) {
words.push_back(temp);
}
cout << words.size();
}
What am I missing, please? Thank you in advance.
Input the strings and when done press Ctrl+Z (followed by Enter) if on Windows or Ctrl+D if on Linux. When you do that the cin>>temp; condition inside your for loop will evaluate to false and your program will exit the loop.
Firstly, it is not necessary to use the std_lib_facilities.h. That is just something used in the book to avoid having every example in the book regularly include a set of standard headers, or to correct for non-standard behaviours between compilers. It is also a header that that does using namespace std - you will find numerous examples (both on SO and the wider internet) explaining why it is VERY poor practice to have using namespace std in a header file.
Second, it is not necessary to use stdafx.h either. That is something generated by Microsoft IDE, and provides a means of speeding up compilation in large projects, because of how it causes the compiler to work with precompiled headers. If you only expect to use Microsoft compilers, then feel free to fill your boots and use this one. However, it is not standard C++, may (depending on IDE and project settings) include windows specific headers that will not work with non-Microsoft compilers, and in forums will probably discourage people who use other compilers from helping you - since they will have good reason to assume your code uses Microsoft-specific extensions, which will mean they probably can't help you.
The first sample of code can be rewritten, in standard C++ (without use of either header above) as
#include <vector> // for std::vector
#include <string> // for std::string
#include <iostream> // std::cout and other I/O facilities
int main()
{
std::vector<std::string> words;
for(std::string temp; std::cin >> temp; )
words.push_back(temp);
std::cout << "Number of words: " << words.size() << '\n';
}
Before you get excited, this will exhibit the same problem (not apparently finishing). The reason is actually the termination condition of the loop - std::cin >> temp will only terminate the loop if end of file or some other error is encountered in the stream.
So, if you type
The cow jumped over the moon
std::cin will continue to wait for input. It is generally necessary for the USER to trigger and end of file condition. Under windows, this requires the user to enter CTRL-Z on an empty line followed by the enter key.
An alternative would be to have some pre-agreed text that cause the loop to exit, such as
#include <vector> // for std::vector
#include <string> // for std::string
#include <iostream> // std::cout and other I/O facilities
int main()
{
std::vector<std::string> words;
for(std::string temp; std::cin >> temp && temp != "zzz"; )
words.push_back(temp);
std::cout << "Number of words: " << words.size() << '\n';
}
which will cause the program to exit when the input contains the word zzz. For example
The cow jumped over the moon zzz
There are other techniques, such as reading one character at a time, and stopping when the user enters two consecutive newlines. That requires your code to interpret every character, and decide what constitutes a word. I'll leave that as an exercise.
Note there is no means in standard C++ to directly read keystrokes - the problems above are related to how standard streams work, and interact with the host system.
The user can also use the program "as is" by placing the same text into an actual file, and (when the program is run) redirect input for your program to come from that file. For example your_executable < filename.
I'm trying to collect user's input in a string variable that accepts whitespaces for a specified amount of time.
Since the usual cin >> str doesn't accept whitespaces, so I'd go with std::getline from <string>
Here is my code:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; i++)
{
string local;
getline(cin, local); // This simply does not work. Just skipped without a reason.
//............................
}
//............................
return 0;
}
Any idea?
You can see why this is failing if you output what you stored in local (which is a poor variable name, by the way :P):
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; i++)
{
string local;
getline(cin, local);
std::cout << "> " << local << std::endl;
}
//............................
return 0;
}
You will see it prints a newline after > immediately after inputting your number. It then moves on to inputting the rest.
This is because getline is giving you the empty line left over from inputting your number. (It reads the number, but apparently doesn't remove the \n, so you're left with a blank line.) You need to get rid of any remaining whitespace first:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
cin >> ws; // stream out any whitespace
for(int i = 0; i < n; i++)
{
string local;
getline(cin, local);
std::cout << "> " << local << std::endl;
}
//............................
return 0;
}
This the works as expected.
Off topic, perhaps it was only for the snippet at hand, but code tends to be more readable if you don't have using namespace std;. It defeats the purpose of namespaces. I suspect it was only for posting here, though.
Declare a character to get in the carriage return after you have typed in the number.char ws;int n;cin>>n;ws=cin.get();
This will solve the problem.
Using cin>>ws instead of ws=cin.get(),will make first character of your string to be in variable ws,instead of just clearing '\n'.
It's quite simple.
U jst need to put a cin.get() at the end of the loop.
Are you hitting enter? If not get line will return nothing, as it is waiting for end of line...
My guess is that you're not reading n correctly, so it's converting as zero. Since 0 is not less that 0, the loop never executes.
I'd add a bit of instrumentation:
int n;
cin >> n;
std::cerr << "n was read as: " << n << "\n"; // <- added instrumentation
for // ...
why this happens :
This happens because you have mixed cin and cin.getline.
when you enter a value using cin, cin not only captures the value, it also captures the newline. So when we enter 2, cin actually gets the string “2\n”. It then extracts the 2 to variable, leaving the newline stuck in the input stream. Then, when getline() goes to read the input, it sees “\n” is already in the stream, and figures we must have entered an empty string! Definitely not what was intended.
old solution :
A good rule of thumb is that after reading a value with cin, remove the newline from the stream. This can be done using the following :
std::cin.ignore(32767, '\n'); // ignore up to 32767 characters until a \n is removed
A better solution :
use this whenever you use std::getline() to read strings
std::getline(std::cin >> std::ws, input); // ignore any leading whitespace characters
std::ws is a input manipulator which tell std::getline() to ignore any leading whitespace characters
source : learncpp website
goto section (Use std::getline() to input text)
hope this is helpful
Is n properly initialized from input?
You don't appear to be doing anything with getline. Is this what you want?
getline returns an istream reference. Does the fact that you're dropping it on the ground matter?
On which compiler did you try this? I tried on VC2008 and worked fine. If I compiled the same code on g++ (GCC) 3.4.2. It did not work properly. Below is the versions worked in both compilers. I dont't have the latest g++ compiler in my environment.
int n;
cin >> n;
string local;
getline(cin, local); // don't need this on VC2008. But need it on g++ 3.4.2.
for (int i = 0; i < n; i++)
{
getline(cin, local);
cout << local;
}
The important question is "what are you doing with the string that gives you the idea that the input was skipped?" Or, more accurately, "why do you think the input was skipped?"
If you're stepping through the debugger, did you compile with optimization (which is allowed to reorder instructions)? I don't think this is your problem, but it is a possibility.
I think it's more likely that the string is populated but it's not being handled correctly. For instance, if you want to pass the input to old C functions (eg., atoi()), you will need to extract the C style string (local.c_str()).
You can directly use getline function in string using delimiter as follows:
#include <iostream>
using namespace std;
int main()
{
string str;
getline(cin,str,'#');
getline(cin,str,'#');
}
you can input str as many times as you want but one condition applies here is you need to pass '#'(3rd argument) as delimiter i.e. string will accept input till '#' has been pressed regardless of newline character.
Before getline(cin, local), just add if(i == 0) { cin.ignore(); }. This will remove the last character (\n) from the string, which is causing this problem and its only needed for the first loop. Otherwise, it will remove last character from the string on every iteration. For example,
i = 0 -> string
i = 1 -> strin
i = 2 -> stri
and so on.
just use cin.sync() before the loop.
just add cin.ignore() before getline and it will do the work
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; i++)
{
string local;
cin.ignore();
getline(cin, local);
}
return 0;
}