I would like to figure out how to read a whole line (including spaces) with std::cin. I am aware of the existence of std::getline, I would just like to figure out how to do it with std::cin so I can better understand iostream in C++. I've tried using a for loop with std::cin, however it keeps reading past the end of the line. Any help would be greatly appreciated.
Also the cin << only allows us to enter one word into a string.
However, there is a cin function that reads text containing blanks.
std::cin.get(name, MAX);
get will read all characters including spaces until Max characters have been read or the end of line character (‘\n’) is reached and will put them into the name variable.
You should decide what is MAX.
Related
I have a problem.
i want the user to enter a number in my c++ program, but during the input i want to prevent that he just presses enter without having made an input, thus creating a line break.
I have already solved the problem in another place where the user has to enter a character.
I have read the character with getchar, determined the position of the cursor with the ANSI escape sequences and provided the whole thing with a do while loop.
But since I want to read in a number between 0 and 250, getchar would not be suitable.
scanf and cin both wait for a valid input and cause these nasty line breaks.
I have already thought about using getchar anyway and storing the characters in a char array whose indices I then convert to the corresponding numbers which I then add up to the actual number which can then be stored again in an int variable.
But surely there is an easier alternative or?
Translated with www.DeepL.com/Translator (free version)
This line will flush the newline character
cin.ignore(256, '\n');
Just started learning C++ and encountered an issue with strings while doing an exercise.
So I initialized std::string phrase; while allowing the user to input and save the phrase to the string with std::cin >> phrase;. Now my issue comes when the inputed phrase has spaces, I noticed that the computer will only save the characters up till the first word only.
With the phrase "sunsets are great", the phrase.size() only came out to 7, so the following words after the first space were not saved.
The entire exercise is supposed to compare all of the letters in the whole inputted string with another set of values. Should I be using a different function for this?
Any help would be appreciated! :)
I have also had this problem when i was first starting out.
whenever you want to read a string i would use the getline.
ie
string phase
cout << "enter phase" <<endl;
getline(cin,phase);
If you want to take an entire line including space(s), you may use the following code:
string str; // declaration
getline(cin, str);
Remember: cin.get and cin will trim all the inputted characters just after first space.
Enjoy.
I learn to program in c++ with previous experience with python and R. Id say I understand for loops well, but now I found out that I do not know nothig about them. Here is piece of code.
for (int i = 0; i != 1; ){
string name;
getline(infile, name);
if (name == end_input){
i = 1;
}
else{
names.push_back(name);
}
}
Whole program should (and do) read names (name) from file infile and store them into names string. Than I want them to store in another file. When I look on the code, I would thing c++ do following instructions:
create integer i and set it to 0
create string name
read the line from infile and store this line into names string vector.
this will repeat unless name == end_input
From this I would say that c++ will store first line in input file again and again because I didnt tell him to jump to next line after getline the first line. But program reads all names from that file, line by line as expected by author. How is that possible?
Thank you.
getline automatically moves to the next line after reading a line.
Also a do while loop might serve your purposes better here.
When an inbuilt function does not behave as you expected, the logical next step should be to check the Documentation. If you do, you will see the following:
Extracts characters from is and stores them into str until the delimitation character delim is found (or the newline character, '\n', for (2)).
The extraction also stops if the end of file is reached in is or if some other error occurs during the input operation.
If the delimiter is found, it is extracted and discarded (i.e. it is not stored and the next input operation will begin after it).
Which answers your Question.
So I'm trying to go through input line by line. Each line in the input is formatted like this:
Words_More words_even more words_What I Need to Go Through_ Random_ Random_Etc.
With a random amount of word clusters (The words separated by '_')
I want, for each line, to be able to ignore all the words until I get to the fourth word cluster which in the example I gave would be: "What I Need To Go Through" and then store those separate words in some data structure that I haven't decided upon yet.
My first thought would be to use
getline(cin, trash, '_');
three times and deal with the data that follows, but then how would I loop line by line until the end of the input?
You basically have two options:
use getline for each line, then parse it
use getline(stream, string) to get a line from your stream, and store it into a string. Then construct an istringstream to parse this again (with the getline you thought of.
get what you need, and then ignore() stuff unill the next newline
You do getline() thing, and then you call ignore() (doc)
to read and discard the rest of the line, so you can start again with the next line.
which one you use is up to you. but the second one has slightly better performance, if you care about that stuff.
I am trying to access different words in a string using std::istringstream and I am also doing so with multiple test cases.
int t;
cin>>t;
while(t--)
{
string arr;
cin.ignore();
getline(cin,arr);
istringstream iss(arr);
string word;
while(iss>>word)
{
cout<<word;
}
}
For the first test case, everything is perfect (i.e. it outputs the correct words). But for every subsequent test case, the first letter of the first word is left out.
Example:
Input:
4
hey there hey
hi hi hi
my name is xyz
girl eats banana
And I'm getting:
Output:
hey there hey
i hi hi
y name is xyz
irl eats banana
Can anyone please suggest me what to do and why is this error occurring?
Your problem is that formatted input, i.e., something like in >> value conventionally skips leading whitespace before attempting to read. Unformatted input, on the other hand, doesn't skip leading whitespace. With the std::cin.ignore(); in your loop you make the assumption that std::getline(std::cin, arr) would leave the newline in the input like the input of t does. That is not so. std::getline() extracts and stores all characters up to the first newline where it stop, still extracting the newline. So, you'd remove the cin.ignore(); from the loop.
The key question becomes how to switch between formatted input and unformatted input. Since the newline upon entry of a numeric value may be preceded with arbitrary spaces which you probably also want to ignore, there are essentially to ways:
std::cin >> std::ws; skips all leading whitespace. That may include multiple newlines and spaces at the beginning of the line. Skipping those may not necessarily desirable.
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); ignores all characters up to and including the first newline. That would allow for empty lines to follow up as well as lines starting with leading whitespace.
This line is the culprit: cin.ignore();.
When std::basic_istream::ignore is called without any arguments, it ignores exactly 1 character.
In your case, std::cin.ignore() will ignore the first letter, but not for the first test case, because at that point std::cin is empty, so there is nothing to ignore. But then, std::cin has the other words in it, so it ignores 1 character from the first word.
According to the documentation of std::basic_istream::ignore:
Extracts and discards characters from the input stream until and
including delim. ignore behaves as an UnformattedInputFunction
Its worth to mention that std::basic_istream::ignore will block and wait for user input if there is nothing to ignore in the stream.
With this in mind, lets break down what your code does:
the first time you call this function in your loop, it is going to
ignore the new line character that is still in the buffer from the
previous cin>>t operation. Then the getline statment will wait and read a line from the user.
The next time around, since there is nothing in the buffer to
ignore(as std::getline doesn't leave the new line character in the
buffer), it is going to block and wait for input to ignore. So
the next time the program block and waits for input, it is because
of the ignore() function,not the getline function as you would
have hoped, and the moment you provide an input(i.e you second test
case),one character from the input is going to be ignored.
The next getline function will not block since there is something
in the buffer left by the previous ignore function after it
ignores the first character of the input so getline will read the
remaining string which will happen to be one character short.
The process continues from step 2 until your loop terminates.
int t;
cin>>t;//this leaves new line character in the buffer
while(t--)
{
string arr;
cin.ignore();//this will ignore one character from the buffer,so the first time
//it will ignore the new line character from the previous cin input
//but next time it will block and wait for input to ignore
getline(cin,arr);//this will not block if there is something in the buffer
//to read
...
}
The solution would be to move the ignore statement out of the loop and next to your cin>>t statement. It's also better write ignore(INT_MAX,'\n'); in this case. You might also want to read this answer to see when and how to use ignore.