Unable to read two strings with cin.get()

Question

sample execution Why does trying to input two strings using cin.get() fails? I can successfully read the first string but the input fails for second string and subsequent operations.. See the code:

#include <iostream>
#include <stdlib.h>

int main(){
long int n,k;
char a[11],b[11];
cin.get(a,11);

n = atoi(a);

cin.get(b,11);
cout<<b;   
k = atoi(b);


cout      << "\ncin.rdstate(): " << cin.rdstate()
      << "\n    cin.eof(): " << cin.eof()
      << "\n   cin.fail(): " << cin.fail()
      << "\n    cin.bad(): " << cin.bad()
      << "\n   cin.good(): " << cin.good() << endl << endl;
}

I am trying to input two strings and store them into long int variables as shown in program, but the cin.get(b,11) fails and stack overflow occurs for k= atoi(b) .Also, you may observe nothing is output for cout<<b .. And, at last cin.fail() is set to 1 , which means I am doing some kind of logical error.. Please help me in rectifying this! Please suggest some method which is fast and meant for c++ only .. (If you feel this question is too bad please mention in comments before down voting this, I am already struggling at 21 rep!)

do you still have the same problem? can you post the new code? — KooKoo, May 08 '15 at 09:00
Also, remember that if you enter a newline to terminate the first input, then the newline will *not* be extracted from the input stream. See e.g. [this `get` reference](http://en.cppreference.com/w/cpp/io/basic_istream/get). — Some programmer dude, May 08 '15 at 09:00
As you are coding in C++, I would recommend using `std::string` rather than C's `char[]` — Levi, May 08 '15 at 09:05
I recommend using [`std::string`](http://en.cppreference.com/w/cpp/string/basic_string) and [`std::getline`](http://en.cppreference.com/w/cpp/string/basic_string/getline) instead. And if you have C++11, then [`std::stoi`](http://en.cppreference.com/w/cpp/string/basic_string/stol) to convert to integer. — Some programmer dude, May 08 '15 at 09:08
is std::string fast enough?? I have to perform 2.5 Mbs of input and output in 3s .. I am doing this for a competition .. — anshabhi, May 08 '15 at 09:13

score 3 · Accepted Answer · answered May 08 '15 at 09:05

3

\n will remain in the buffer after the first cin. You can solve this problem by adding an empty cin.get()

cin.get(a,11);
n = atoi(a);
cin.get();
cin.get(b,11);
cout<<b;   
k = atoi(b);

answered May 08 '15 at 09:05

Praveen Kumar

121
1
7

score 1 · Answer 2 · edited May 23 '17 at 12:14

1

cin.get() Does not extract the delimiter from the input (documentation).

If you are C++ with streams it makes sense to use the built in functionality. In particular, C++ offers formatted I/O. To read two numbers you should use:

long int a, b;
cin >> a;
cin >> b;

This will read two numbers from the standard input.

If speed is a concern, try to turn off C I/O synchronisation: std::ios::sync_with_stdio(false); There is an interesting benchmark here that shows that if you turn of synchronisation with C I/O, streams are actually pretty fast.

edited May 23 '17 at 12:14

Community

1
1

answered May 08 '15 at 09:12

Roman Kutlak

2,684
1
19
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because of being formatted, cin is very slow for high volume operations.. I obviously know cin .. I started c++ with that only!! – anshabhi May 08 '15 at 09:15
1

thats superb! I just wanted the c speed in c++ and got it!! – anshabhi May 08 '15 at 09:39

Unable to read two strings with cin.get()

2 Answers2