CODEWITHSUNDEEP
c++inputiostream
Guille
Guille

Reputation: 63

How to read until EOF from cin in C++

I am coding a program that reads data directly from user input and was wondering how could I (without loops) read all data until EOF from standard input. I was considering using cin.get( input, '\0' ) but '\0' is not really the EOF character, that just reads until EOF or '\0', whichever comes first.

Or is using loops the only way to do it? If so, what is the best way?

Upvotes: 105

Views: 289626

Answers (11)

Richard Smith
Richard Smith

Reputation: 49682

After researching KeithB's solution using std::istream_iterator, I discovered the std:istreambuf_iterator.

Test program to read all piped input into a string, then write it out again:

#include <iostream>
#include <iterator>
#include <string>

int main()
{
  std::istreambuf_iterator<char> begin(std::cin), end;
  std::string s(begin, end);
  std::cout << s;
}

istreambuf_iterator bypasses a bunch of locale and formatting processing, it's essentially a lower level version of istream_iterator, and for the purpose of reading stdin until EOF with no intermediate processing it's more suitable out of the box.

Upvotes: 46

dimon-ksi
dimon-ksi

Reputation: 1

One line for loop:

for( std::string line; std::getline(std::cin, line); std::cout << line << std::endl );

Upvotes: 0

trotterdylan
trotterdylan

Reputation: 1101

The only way you can read a variable amount of data from stdin is using loops. I've always found that the std::getline() function works very well:

std::string line;
while (std::getline(std::cin, line))
{
    std::cout << line << std::endl;
}

By default getline() reads until a newline. You can specify an alternative termination character, but EOF is not itself a character so you cannot simply make one call to getline().

Upvotes: 100

FrankHB
FrankHB

Reputation: 2495

Probable simplest and generally efficient:

#include <iostream>
int main()
{
    std::cout << std::cin.rdbuf();
}

If needed, use stream of other types like std::ostringstream as buffer instead of standard output stream here.

Upvotes: 7

0xbadf00d
0xbadf00d

Reputation: 18178

One option is to a use a container, e.g.

std::vector<char> data;

and redirect all input into this collection until EOF is received, i.e.

std::copy(std::istream_iterator<char>(std::cin),
    std::istream_iterator<char>(),
    std::back_inserter(data));

However, the used container might need to reallocate memory too often, or you will end with a std::bad_alloc exception when your system gets out of memory. In order to solve these problems, you could reserve a fixed amount N of elements and process these amount of elements in isolation, i.e.

data.reserve(N);    
while (/*some condition is met*/)
{
    std::copy_n(std::istream_iterator<char>(std::cin),
        N,
        std::back_inserter(data));

    /* process data */

    data.clear();
}

Upvotes: 0

derpface
derpface

Reputation: 1691

Wait, am I understanding you correctly? You're using cin for keyboard input, and you want to stop reading input when the user enters the EOF character? Why would the user ever type in the EOF character? Or did you mean you want to stop reading from a file at the EOF?

If you're actually trying to use cin to read an EOF character, then why not just specify the EOF as the delimiter?

// Needed headers: iostream

char buffer[256];
cin.get( buffer, '\x1A' );

If you mean to stop reading from a file at the EOF, then just use getline and once again specify the EOF as the delimiter.

// Needed headers: iostream, string, and fstream

string buffer;

    ifstream fin;
    fin.open("test.txt");
    if(fin.is_open()) {
        getline(fin,buffer,'\x1A');

        fin.close();
    }

Upvotes: 1

Bryan
Bryan

Reputation: 1

while(std::cin) {
 // do something
}

Upvotes: 0

liborm
liborm

Reputation: 2724

Sad side note: I decided to use C++ IO to be consistent with boost based code. From answers to this question I chose while (std::getline(std::cin, line)). Using g++ version 4.5.3 (-O3) in cygwin (mintty) i got 2 MB/s throughput. Microsoft Visual C++ 2010 (/O2) made it 40 MB/s for the same code.

After rewriting the IO to pure C while (fgets(buf, 100, stdin)) the throughput jumped to 90 MB/s in both tested compilers. That makes a difference for any input bigger than 10 MB...

Upvotes: 4

Degvik
Degvik

Reputation: 3180

Using loops:

#include <iostream>
using namespace std;
...
// numbers
int n;
while (cin >> n)
{
   ...
}
// lines
string line;
while (getline(cin, line))
{
   ...
}
// characters
char c;
while (cin.get(c))
{
   ...
}

resource

Upvotes: 72

luke
luke

Reputation: 37443

You can use the std::istream::getline() (or preferably the version that works on std::string) function to get an entire line. Both have versions that allow you to specify the delimiter (end of line character). The default for the string version is '\n'.

Upvotes: 2

KeithB
KeithB

Reputation: 17007

You can do it without explicit loops by using stream iterators. I'm sure that it uses some kind of loop internally.

#include <string>
#include <iostream>
#include <istream>
#include <ostream>
#include <iterator>

int main()
{
// don't skip the whitespace while reading
  std::cin >> std::noskipws;

// use stream iterators to copy the stream to a string
  std::istream_iterator<char> it(std::cin);
  std::istream_iterator<char> end;
  std::string results(it, end);

  std::cout << results;
}

Upvotes: 58

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