I am trying to read a line of string characters with numbers (e.g "30 40 50 20") and put them into a vector. I also need to avoid empty space and newlines. But when I read the input, it doesn't see the string "30", it sees the characters "3" and "4".
void Input() {
getline(cin,line, '\n');
for (int i = 0; i < line.length(); i++) {
if (! (isspace(line[i]))) {
cout << line[i] << ", ";
scores.push_back(line[i]);//(atoi(input));
}
}
cout << scores.size() << "! ";
}
A line like "30 40 50" won't give a vector size of 3, it will give a size of 6.
What are the optimal ways to get around this issue?
EDIT: I should have clarified in the original message that this is for a challenge, in which I am unable to include the string stream library in the original case.
I think you're doing the right thing grabbing the whole line before parsing, otherwise you get into a bit of a pickle. But you do actually have to do some parsing. Right now you're just pulling out individual characters.
The following isn't optimal but it'll get you started — continue using formatted stream extraction, but isolated to this line from the file.
So:
void Input()
{
getline(cin, line, '\n');
istringstream ss(line);
int val;
while (ss >> val)
scores.push_back(val);
cout << scores.size() << "! ";
}
Read the line and put into a std::istringstream, then read as "normally" using the >> operator from the string stream.
Putting the line into a std::istringstream and extracting the numbers from that is the best way.
Here's an alternative to a manual loop using the standard library:
std::istringstream numbers(line);
std::copy(std::istream_iterator<int>(numbers),
std::istream_iterator<int>(),
std::back_inserter(scores));
It is probably best to take advantage of an input stringsteam, example: http://www.cplusplus.com/reference/sstream/stringstream/stringstream/.
The extraction operator allows you to parse data from the stream to some variable of datatype T. Another advantage of input stringstreams is the ability to query whether the pass was successful, and in your case ignore whitespace characters by setting the skipws format flag.
Example:
int main () {
std::istringstream ss("30 40 50");
float val = 0.0f;
while( ss >> std::skipws >> val )
{
std::cout << val << "\n";
}
return 0;
}
Out: 30 40 50
Related
I'm trying to create a program to separate a single line into a vector of strings separated by the blank spaces in said line, so turn:
foo bar
into
["foo", "bar"]
This is what I have so far:
string command;
string command_temp;
vector<string> command_seperated;
std::cin >> command;
for (int i = 0; i < command.length(); i++){
if (isspace(command[i])){
cout << "blankspace" << endl; command_seperated.push_back(command_temp);
command_temp.clear();
}
command_temp.push_back(command[i]);
for (int i = 0; i < command_temp.size(); i++){
cout << command_temp[i];
}
cout << endl;
}
for (int i = 0; i < command_seperated.size(); i++){
cout << command_seperated[i] << endl;
}
But, if I input "foo bar" when prompted, this just returns:
foo bar
f
fo
foo
Process returned 0 (0x0) execution time : 2.596 s
Press any key to continue
I assume the reason the last for loop isn't printing anything is that there's nothing in it and the push_back to command_seperated isn't working. I have no idea why.
I also don't know why the entire program seems to just stop working after the first blank space.
Using this to refresh my rudimentary C++ skills, so I would appreciate an explanation of why I'm wrong, rather than a more elegant alternative solution.
What you are seeing is normal behavior of operator>>, which is used for reading formatted input. It skips leading whitespace (if the skipws flag is enabled on the stream, which it normally is), then reads until EOF or whitespace is encountered. So, in your example, std::cin >> command receives only foo even though you entered foo bar. If you invoked std::cin >> command a 2nd time, you would receive bar.
To read a string that contains whitespace in it, use std::getline() instead:
std::getline(std::cin, command);
It does not skip leading whitespace, and reads until EOF or a linebreak (ie, from typing Enter) is encountered.
That being said, the parsing code you have shown can be greatly simplified if you use a std::istringstream with operator>> to parse the command, eg:
std::string command, token;
std::vector<std::string> command_seperated;
std::getline(std::cin, command);
std::istringstream iss(command);
while (iss >> token) {
command_seperated.push_back(token);
}
for (const auto &str : command_seperated){
cout << str << endl;
}
This may be a very simplistic question, but I have not found any examples to guide me. I am trying to write class in C++ that can read a text file where columns of data (float, char, int, etc...) are separated by spaces. I would like the class to be able to ignore some columns and read in specified columns. For now I am experimenting with one and two column formats and progressing from there. A brief example of a test input file is listed below.
103.816
43.984
2214.5
321.5
615.8
8.186
37.6
My first attempt at writing a code to read in one column of data is trivial and looks like this.
void Read_Columnar_File::Read_File(const std::string& file_name)
{
int i;
std::ifstream inp(file_name,std::ios::in | std::ios::binary);
if(inp.is_open()) {
std::istream_iterator<float> start((inp)), end;
std::vector<float> values(start,end);
for(i=0; i < 7; i++) std::cout << values[i] << std::endl;
}
else std::cout << "Cannot Open " << file_name << std::endl;
inp.close();
}
In my next attempt I am trying to read in only one column of a two column format like the input shown below. The numbers are just made up for this example
103.816 34.18
43.984 21.564
2214.5 18.5
321.5 1.00
615.8 4.28
8.186 1.69
37.6 35.48
I modified the code format slightly to look like the example below. I am using a brief but of pseudocode after the inp >> statement to illustrate that I am trying to get the code to skip to the next line after reading in the first column. my question is "How do I get the code to just read the first column and then skip to the next line where again it just reads the first column of data and make it keep doing this until the end of file?" And thank you in advance for any advice that you can give.
void Read_Columnar_File::Read_File(const std::string& file_name)
{
int i;
float input;
std::vector<float> values;
std::ifstream inp(file_name,std::ios::in | std::ios::binary);
if(inp.is_open()) {
for(i=0; i < 7; i++) {
inp >> input >> \\ - At this point I want the code to skip to the next
\\ line of the input file to only read the first column
\\ of data
values.push_back(input);
}
for(i=0; i < 7; i++) std::cout << values[i] << std::endl;
}
else std::cout << "Cannot Open " << file_name << std::endl;
inp.close();
}
You can use the member function ignore() to discard all the characters until the next line. I would also fix up your code to use a for() loop predicated on the success of the extraction so your code will work for any number of columns, not just 7:
for (float input; inp >> input; values.push_back(input))
{
inp.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
When you want to read only part of a line, and skip the rest of that line, one easy starting point is to:
read the entire line into a string
put the whole string into an istringstream
Parse out the parts you care about
Repeat
As a rule, I generally find this easier to generalize than ones that alternate between reading and ignoring data as it's being read from the file.
I am new to programming in C++.
I am trying to ask the user an input (for example):
std::string numbers;
std::cout << What is your favorite number;
std::cin >> numbers
If the user entered
1, 2, 3
How do I extract only the number "2"? I know in python, you would do something like numbers[1], but is there a same way in C++ as well?
So, "what are your favorite numbers?"
The idea is the same as in python or any other language: split the input line by the separator character, trim if you care, and finally get the element you want, if it exists.
Splitting a string by a character
Eventually, trim
Finally, you should have a vector of string, and you can get the second with v[1] or similar, checking if it exists
you can get the length of string by numbers.length().
then you can use for loop.
for(int i =0 ; i < numbers.length();i++)
{
if(numbers[i] == '2')
// do what you want you do here with 2
}
Keep in mind, your cin won't get entire "1, 2, 3" string because of whitespace. You should use getline instead of cin.
such as..
getline(cin, numbers,'\n');
To catch a line of numbers:
int main()
{
std::vector<int> numbers;
std::string line;
std::getline(std::cin, line); // First read the whole line of input
std::stringstream linestream(line); // Set up to parse the line
int number;
while(linestream >> number) { // Read a number
char x; // for the comma
linestream >> x; // remove the comma
numbers.push_back(number); // Add to the vector (array)
}
// Print the number
std::cout << "The second number is: " << numbers[1] << "\n"; // vectors are 0 indexed
}
I have been working on this for a while and can't fix it. I am very new to C++. So far I can get 10 things into my array but the output is not legible, it's just a bunch of numbers. I have read other posts with similar code but for some reason mine isn't working.
The input text file is 10 lines of fake data like this:
56790 "Comedy" 2012 "Simpsons" 18.99 1
56791 "Horror" 2003 "The Ring" 11.99 7
My code is here:
(My output is below my code)
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
struct DVD {
int barcode;
string type;
int releaseDate;
string name;
float purchaseprice;
int rentaltime;
void printsize();
};
int main () {
ifstream in("textfile.exe");
DVD c[10];
int i;
for (int i=0; i < 10; i++){
in >> c[i].barcode >> c[i].type >> c[i].releaseDate >>
c[i].name >> c[i].purchaseprice >> c[i].rentaltime;
}
for (int i=0;i< 10;i++) {
cout << c[i].barcode<<" ";
cout << c[i].type<<" ";
cout << c[i].releaseDate<<" ";
cout << c[i].name << " ";
cout << c[i].purchaseprice << " ";
cout << c[i].rentaltime << "\n";
}
return 0;
}
My output looks similar to garbage, but there are 10 lines of it like my array:
-876919876 -2144609536 -2.45e7 2046
A comment on what to study to modify my code would be appreciated.
As suggested by cmbasnett, ifstream in("textfile.exe") reads in an executable file. If you with for the program to read in a text file, changing it to ifstream in("textfile.txt") should work.
You always need to check that your input is actually correct. Since it may fail prior to reading 10 lines, you should probably also keep a count of how many entries you could successfully read:
int i(0);
for (; i < 10
&& in >> c[i].barcode >> c[i].type >> c[i].releaseDate
>> c[i].name >> c[i].purchaseprice >> c[i].rentaltime; ++i) {
// ???
}
You actual problem reading the second line is that your strings are quoted but the approach used for formatted reading of strings doesn't care about quotes. Instead, strings are terminated by a space character: the formatted input for strings will skip leading whitespace and then read as many characters until another whitespace is found. On your second line, it will read "The and then stop. The attempt to read the purchaseprice will fail because Ring isn't a value numeric value.
To deal with that problem you might want to make the name quotedstring and define an input and output operators for it, e.g.:
struct quoted_string { std::string value; };
std::istream& operator>> (std::istream& in, quoted_string& string) {
std::istream::sentry cerberos(in); // skips leading whitespace, etc.
if (in && in.peek() == '"') {
std::getline(in.ignore(), string.value, '"');
}
else {
in.setstate(std::ios_base::failbit);
}
return in;
}
std::ostream& operator<< (std::ostream& out, quoted_string const& string) {
return out << '"' << string.value << '"';
}
(note that the code isn't test but I'm relatively confident that it might work).
Just to briefly explain how the input operator works:
The sentry is used to prepare the input operation:
It flushes the tie()d std::ostream (if any; normally there is none except for std::cin).
It skips leading whitespace (if any).
It checks if the stream is still not in failure mode (i.e., neither std::ios_base::failbit nor `std::ios_base::badbit are set).
To see if the input starts with a quote, in.peek() is used: this function returns an int indicating either that the operation failed (i.e., it returns std::char_traits<char>::eof()) or the next character in the stream. The code just checks if it returns " as it is a failure if the stream returns an error or any other character is present.
If there is a quote, the quote is skipped using file.ignore() which by default just ignores one character (it can ignore more characters and have a character specified when to stop).
After skipping the leading quote, std::getline() is used to read from file into string.value until another quote is found. The last parameter is defaulted to '\n' but for reading quoted string using a '"' is the correct value to use. The terminating character is, conveniently, not stored.
I have a text file with a line like:
James Dean 10 Automotive 27010.43
and I need to read that file and put each of the 4 above into arrays.
char nameArray[MAX][NAME_MAX];
int yearArray[MAX];
char departmentArray[MAX][DEP_MAX];
double payArray[MAX];
while(i < MAX && infile) {
infile.getline(nameArray[i], 20);
infile >> yearArray[i];
infile.getline(departmentArray[i], 15);
infile >> payArray[i];
cout << nameArray[i] << " " << yearArray[i] << " " << departmentArray[i] << " " << fixed << setprecision(2) << payArray[i] << endl;
i++;
}
The code is cut down just to give you an idea of what I am trying to do, but when I run this, I get something like:
James Dean -858993460 -92559631349317830000000000000000000000000000
000000000000000000.00
Thanks for the help.
==== Edit ==========================================
I changed from getline to get, thanks for that. I have to use get and not >> because some of the lines I am reading in are more than just "James Dean", they are up to 20 char long...ex: "William K. Woodward" is another one.
So, if I just use get, then it reads the first line in fine, but then I get the same messed up text for the second line.
Here is the code:
infile.get(nameArray[i], 20);
infile >> yearArray[i];
infile.get(departmentArray[i], 15);
infile >> payArray[i];
The getline functions takes an input stream and a string to write to. So, two getline calls read in two lines. Your input mechanism is broken. Either, use getline or the stream extraction operator (i.e. >>) but not both.
If you plan to use getline you need to parse the string (which is effectively one line of input) into tokes, and then store them in appropriately typed arrays. The second and fourth tokens are numbers, hence you will need to convert these from string to int or double.
The operator >> approach:
string name, surname;
int year;
double pay;
while (infile) {
infile >> name >> surname >> year >> department >> pay;
namearray[ i ] = name + " " + surname;
// ...
payarray[ i ] = pay;
++i;
}
The getline approach:
string line;
while (getline(infile, line)) {
parse(line, tokens);
namearray[ i ] = token[ 0 ] + " " + token[ 1 ];
// ...
payarray[ i ] = strTodouble(token[ 4 ]);
++i;
}
// parse definition
void parse(string line, vector<string>& token) {
// roll your own
}
double strToDouble(string s) {
// ...
}
I dont see where you define infile but I will assume that it is an ifile . In that case you should use it the same way u use cin to get input.
Why do you do a getline () ?
That function will stop only at an '\n' char or at an EOF char. So it means, you start reading the int after the end of the line, some random data.
Correct me if i'm wrong, but are there 20 or 19 characters in that first string (James Dean) before the number (10) ?