I have for example the following piece of code:
string str;
int i;
cout<<"input:";
cin>>str;
cout<<"integer:";
cin>>i;
There is actually nothing wrong with this code, but if I paste some text into the command prompt in "input", it automatically fills some of the copied text into "integer". How can I solve this?
Edit: I can type texts as long as I want, but when I copy texts it goes wrong. I don't know why.
I guess, your text contains white spaces. So, std::cin will not work here. Use std::getline instead.
std::string str;
std::getline( std::cin, str );
There's a third parameter of std::getline - delimiter. By default, it's the new line char.
If your text does contain new line chars, than this will not work. You have 2 options:
find unique char, that may be used as delimiter and pass it as third parameter of std::getline
read line by line (using std::getline) from the user input (std::cin) and look for some special string, that will tell your program where the text ends. There's no other way to know where does the integer start (unless the text is with fixed size, but I doubt that)
string str;
int i;
cout<<"input:";
getline(cin, str);
// you want to read the whole line, operator>> will read until whitespace
cout<<"integer:";
cin>>i;
Related
ifstream InPut;
ofstream OutPut;
InPut.open("/Users/apple/Documents/Lập trình C++/OOP/Tập tin/Test1/Test1/FileIn.txt",ios_base::in);
string str, mssv;
getline(InPut,str);
InPut.seekg(1,ios_base::cur);
getline(InPut,mssv);
InPut.close();
cout<<""<<str<<"/"<<mssv;
return 0;
FileIn.txt:
Nguyen Xuan Sang-1520159
I just want to read "Nguyen Xuan Sang", but my code reads in all of FileIn.txt.
Computers can't read your mind. You never told it to read to the "-", so the computer has no way of knowing at all if you want to read until a space, line break, or something else.
getline() defaults to using a nextline as the delimiter, which in your case seems to cause it to read the whole file.
To tell getline() to read until a "-", specify the character as the third argument like this:
getline(InPut, str, '-');
Basically my issue is that I'm trying to read in data from a .txt file that's full of numbers and comments and store each line into a string vector, but my getline function stops reading at the first whitespace character so a comment like (* comment *) gets broken up into
str[0] = "(*";
str[1] = "comment";
str[2] = "*)";
This is what my codeblock for the getline function looks like:
int main() {
string line;
string fileName;
cout << "Enter the name of the file to be read: ";
cin >> fileName;
ifstream inFile{fileName};
istream_iterator<string> infile_begin {inFile};
istream_iterator<string> eof{};
vector<string> data {infile_begin, eof};
while (getline(inFile, line))
{
data.push_back(line);
}
And this is what the .txt file looks like:
101481
10974
1013
(* comment *) 0
28292
35040
35372
0000
7155
7284
96110
26175
I can't figure out why it's not reading the whole line.
This is for the very simple reason that your code is not using std::getline to read the input file.
If you look at your code very carefully, you will see that before you even get to that point, your code constructs an istream_iterator<string> on the file, and by passing it, and the ending istream_iterator<string> value to the vector's constructor, this effectively swallows the entire file, one whitespace-delimited word at a time, into the vector.
And by the time things get around to the getline loop, the entire file has already been read, and the loop does absolutely nothing. Your getline isn't really doing anything, with the current state of affairs.
Get rid of that stuff that involves istream_iterators, completely, and simply let getline do the job it was intended for.
string numbers;
string fileName = "text.txt";
ifstream inputFile;
inputFile.open(fileName.c_str(),ios_base::in);
inputFile >> numbers;
inputFile.close();
cout << numbers;
And my text.txt file is:
1 2 3 4 5
basically a set of integers separated by tabs.
The problem is the program only reads the first integer in the text.txt file and ignores the rest for some reason. If I remove the tabs between the integers it works fine, but with tabs between them, it won't work. What causes this? As far as I know it should ignore any white space characters or am I mistaken? If so is there a better way to get each of these numbers from the text file?
When reading formatted strings the input operator starts with ignoring leading whitespace. Then it reads non-whitespace characters up to the first space and stops. The non-whitespace characters get stored in the std::string. If there are only whitespace characters before the stream reaches end of file (or some error for that matter), reading fails. Thus, your program reads one "word" (in this case a number) and stops reading.
Unfortunately, you only said what you are doing and what the problems are with your approach (where you problem description failed to cover the case where reading the input fails in the first place). Here are a few things you might want to try:
If you want to read multiple words, you can do so, e.g., by reading all words:
std::vector<std::string> words;
std::copy(std::istream_iterator<std::string>(inputFile),
std::istream_iterator<std::string>(),
std::back_inserter(words));
This will read all words from inputFile and store them as a sequence of std::strings in the vector words. Since you file contains numbers you might want to replace std::string by int to read numbers in a readily accessible form.
If you want to read a line rather than a word you can use std::getline() instead:
if (std::getline(inputFile, line)) { ... }
If you want to read multiple lines, you'd put this operation into a loop: There is, unfortunately, no read-made approach to read a sequence of lines as there is for words.
If you want to read the entire file, not just the first line, into a file, you can also use std::getline() but you'd need to know about one character value which doesn't occur in your file, e.g., the null value:
if (std::getline(inputFile, text, char()) { ... }
This approach considers a "line" a sequence of characters up to a null character. You can use any other character value as well. If you can't be sure about the character values, you can read an entire file using std::string's constructor taking iterators:
std::string text((std::istreambuf_iterator<char>(inputFile)),
std::istreambuf_iterator<char>());
Note, that the extra pair of parenthesis around the first parameter is, unfortunately, necessary (if you are using C++ 2011 you can avoid them by using braces, instead of parenthesis).
Use getline to do the reading.
string numbers;
if (inputFile.is_open())//checking if open
{
getline (inputFile,numbers); //fetches entire line into string numbers
inputFile.close();
}
Your program does behave exactly as in your description : inputFile >> numbers; just extract the first integer in the input file, so if you suppress the tab, inputFile>> will extract the number 12345, not 5 five numbers [1,2,3,4,5].
a better method :
vector< int > numbers;
string fileName = "text.txt";
ifstream inputFile;
inputFile.open(fileName.c_str(),ios_base::in);
char c;
while (inputFile.good()) // loop while extraction from file is possible
{
c = inputFile.get(); // get character from file
if ( inputFile.good() and c!= '\t' and c!=' ' ) // not sure of tab and space encoding in C++
{
numbers.push_back( (int) c);
}
}
inputFile.close();
once again I ask for help. I haven't coded anything for sometime!
Now I have a text file filled with random gibberish. I already have a basic idea on how I will count the number of occurrences per word.
What really stumps me is how I will determine what line the word is in. Gut instinct tells me to look for the newline character at the end of each line. However I have to do this while going through the text file the first time right? Since if I do it afterwords it will do no good.
I already am getting the words via the following code:
vector<string> words;
string currentWord;
while(!inputFile.eof())
{
inputFile >> currentWord;
words.push_back(currentWord);
}
This is for a text file with no set structure. Using the above code gives me a nice little(big) vector of words, but it doesn't give me the line they occur in.
Would I have to get the entire line, then process it into words to make this possible?
Use a std::map<std::string, int> to count the word occurrences -- the int is the number of times it exists.
If you need like by line input, use std::getline(std::istream&, std::string&), like this:
std::vector<std::string> lines;
std::ifstream file(...) //Fill in accordingly.
std::string currentLine;
while(std::getline(file, currentLine))
lines.push_back(currentLine);
You can split a line apart by putting it into an std::istringstream first and then using operator>>. (Alternately, you could cobble up some sort of splitter using std::find and other algorithmic primitaves)
EDIT: This is the same thing as in #dash-tom-bang's answer, but modified to be correct with respect to error handing:
vector<string> words;
int currentLine = 1; // or 0, however you wish to count...
string line;
while (getline(inputFile, line))
{
istringstream inputString(line);
string word;
while (inputString >> word)
words.push_back(pair(word, currentLine));
}
Short and sweet.
vector< map< string, size_t > > line_word_counts;
string line, word;
while ( getline( cin, line ) ) {
line_word_counts.push_back();
map< string, size_t > &word_counts = line_word_counts.back();
istringstream line_is( line );
while ( is >> word ) ++ word_counts[ word ];
}
cout << "'Hello' appears on line 5 " << line_word_counts[5-1]["Hello"]
<< " times\n";
You're going to have to abandon reading into strings, because operator >>(istream&, string&) discards white space and the contents of the white space (== '\n' or != '\n', that is the question...) is what will give you line numbers.
This is where OOP can save the day. You need to write a class to act as a "front end" for reading from the file. Its job will be to buffer data from the file, and return words one at a time to the caller.
Internally, the class needs to read data from the file a block (say, 4096 bytes) at a time. Then a string GetWord() (yes, returning by value here is good) method will:
First, read any white space characters, taking care to increment the object's lineNumber member every time it hits a \n.
Then read non-whitespace characters, putting them into the string object you'll be returning.
If it runs out of stuff to read, read the next block and continue.
If the you hit the end of file, the string you have is the whole word (which may be empty) and should be returned.
If the function returns an empty string, that tells the caller that the end of file has been reached. (Files usually end with whitespace characters, so reading whitespace characters cannot imply that there will be a word later on.)
Then you can call this method at the same place in your code as your cin >> line and the rest of the code doesn't need to know the details of your block buffering.
An alternative approach is to read things a line at a time, but all the read functions that would work for you require you to create a fixed-size buffer to read into beforehand, and if the line is longer than that buffer, you have to deal with it somehow. It could get more complicated than the class I described.
Using type std::string to accept a sentence, for practice (I haven't worked with strings in C++ much) I'm checking if a character is a vowel or not. I got this:
for(i = 0; i <= analyse.length(); i++) {
if(analyse[i] == 'a' || analyse[i] == 'e' [..etc..]) {
...vowels++;
} else { ...
...consonants++;
}
This works fine if the string is all one word, but the second I add a space (IE: aeio aatest) it will only count the first block and count the space as a consonant, and quit reading the sentence (exiting the for loop or something).
Does a space count as no character == null? Or some oddity with std::string?, It would be helpful to know why that is happening!
EDIT:
I'm simply accepting the string through std::cin, such as:
std::string analyse = "";
std::cin >> analyse;
I'd guess you're reading your string with something like your_stream >> your_string;. Operator >> for strings is defined to work (about) the same as scanf's %s conversion, which reads up until it encounters whitespace -- therefore, operator>> does the same.
You can read an entire line of input instead with std::getline. You might also want to look at an answer I posted to a previous question (provides some alternatives to std::getline).
I can't tell from the code that you have pasted, but I'm going to go out on a limb and guess that you're reading into the string using the stream extraction operator (stream >> string).
The stream extraction operator stops when it encounters whitespace.
If this isn't what's going on, can you show us how you're populating your string, and what its contents are?
If I'm right, then you're going to want a different method of reading content into the string. std::getline() is probably the easiest method of reading from a file. It stops at newlines instead of at whitespace.
Edit based on edited question:
use this (doublecheck the syntax. I'm not in front of my compiler.):
std::getline(std::cin, analyze);
This ought to stop reading when you press "enter".
If you want to read in an entire line (including the blanks) then you should read using getline. Schematically it looks like this:
#include <string>
istream& std::getline( istream& is, string& s );
To read the whole line you do something like this:
string s;
getline( cin, s );
cout << "You entered " << s << endl;
PS: the word is "consonant", not "consenent".
The >> operator on an istream separates strings on whitespace. If you want to get a whole line, you can use readline(cin,destination_string).