read input separated by whitespace(s) or newline…?

问题:

I'm grabbing input from a standard input stream. Such as,

1 2 3 4 5

or

1
2
3
4
5

I'm using:

std::string in;
std::getline(std::cin, in);

But that just grabs upto the newline, correct? How can I get input whether they are separated by newline OR whitespace(s) using only iosteam, string, and cstdlib?

回答1:

Just use:

your_type x;
while (std::cin >> x)
{
    // use x
}

operator>> will skip whitespace by default. You can chain things to read several variables at once:

if (std::cin >> my_string >> my_number)
    // use them both

getline() reads everything on a single line, returning that whether it's empty or contains dozens of space-separated elements. If you provide the optional alternative delimiter ala getline(std::cin, my_string, ' ') it still won't do what you seem to want, e.g. tabs will be read into my_string.

Probably not needed for this, but a fairly common requirement that you may be interested in sometime soon is to read a single newline-delimited line, then split it into components...

std::string line;
while (std::getline(std::cin, line))
{
    std::istringstream iss(line);
    first_type first_on_line;
    second_type second_on_line;
    third_type third_on_line;
    if (iss >> first_on_line >> second_on_line >> third_on_line)
        ...
}

回答2:

Use 'q' as the the optional argument to getline.

#include <iostream>
#include <sstream>

int main() {
    std::string numbers_str;
    getline( std::cin, numbers_str, 'q' );

    int number;
    for ( std::istringstream numbers_iss( numbers_str );
          numbers_iss >> number; ) {
        std::cout << number << ' ';
    }
}

http://ideone.com/I2vWl

回答3:

std::getline( stream, where to?, delimiter ie

std::string in;
std::getline(std::cin, in, ' '); //will split on space

or you can read in a line, then tokenize it based on whichever delimiter you wish.

回答4:

the user pressing enter or spaces is the same.

int count = 5;
int list[count]; // array of known length
cout << "enter the sequence of " << count << " numbers space separated: ";
// user inputs values space separated in one line.  Inputs more than the count are discarded.
for (int i=0; i<count; i++) {
    cin >> list[i];
}

回答5:

#include <iostream>

using namespace std;

string getWord(istream& in) 
{
    int c;

    string word;

    // TODO: remove whitespace from begining of stream ?

    while( !in.eof() ) 
    {

        c = in.get();

        if( c == ' ' || c == '\t' || c == '\n' ) break;

        word += c;
    }

    return word;
}

int main()
{
    string word;

    do {

        word = getWord(cin);

        cout << "[" << word << "]";

    } while( word != "#");

    return 0;
}

回答6:

int main()
{
    int m;
    while(cin>>m)
    {
    }
}

This would read from standard input if it space separated or line separated .