std::cin. eof() tests for end-of-file (hence eof), not for errors.
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() .
The cin is an object which is used to take input from the user but does not allow to take the input in multiple lines. To accept the multiple lines, we use the getline() function. It is a pre-defined function defined in a <string.
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()
.
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
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;
}
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;
}
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.
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...
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