Read all integers from string c++

Question

I need some help with getting all the integers from a std::string and getting each of those integer into an int variable.

String example:

<blah> hi 153 67 216

I would like the program to ignore the "blah" and "hi" and store each of the integers into an int variable. So it comes out to be like:

a = 153
b = 67
c = 216

Then i can freely print each separately like:

printf("First int: %d", a);
printf("Second int: %d", b);
printf("Third int: %d", c);

Thanks!

Search this website. This has been asked and answered thousands of times. — Kerrek SB, Jun 26 '13 at 22:04
@0x499602D2 it could be anything "sdnjid blah hi 23 35 2" it was just an example — Mike, Jun 26 '13 at 22:07

David G · Accepted Answer · 2013-06-28T13:26:05.897

8

You can create your own function that manipulates a std::ctype facet by using its scan_is method. Then you can return the generated string to a stringstream object and insert the contents to your integers:

#include <iostream>
#include <locale>
#include <string>
#include <sstream>
#include <algorithm>
#include <iterator>
#include <cstring>

std::string extract_ints(std::ctype_base::mask category, std::string str, std::ctype<char> const& facet)
{
    using std::strlen;

    char const *begin = &str.front(),
               *end   = &str.back();

    auto res = facet.scan_is(category, begin, end);

    begin = &res[0];
    end   = &res[strlen(res)];

    return std::string(begin, end);
}

std::string extract_ints(std::string str)
{
    return extract_ints(std::ctype_base::digit, str,
         std::use_facet<std::ctype<char>>(std::locale("")));
}

int main()
{
    int a, b, c;

    std::string str = "abc 1 2 3";
    std::stringstream ss(extract_ints(str));

    ss >> a >> b >> c;

    std::cout << a << '\n' << b << '\n' << c;
}

Output:

1 2 3

Demo

edited Jun 28 '13 at 13:26

answered Jun 26 '13 at 22:50

David G

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...but It's missing `#include ` for `std::back_inserter` – Captain Obvlious Jun 26 '13 at 23:02
@Mike Yes, this code will work for gcc-4.7.2+. Is this code not compiling for you? Are you getting any errors? – David G Jun 26 '13 at 23:57
@0x499602D2 It is not compiling, im using gcc-4.2.1 – Mike Jun 26 '13 at 23:59
@Mike Replace the `auto` with `char const*`. – David G Jun 27 '13 at 00:02
@0x499602D2 now its 2 errors: 'struct std::string' has no member named 'front' and 'struct std::string' has no member named 'back' – Mike Jun 27 '13 at 00:08
Wow, you should upgrade your compiler lol. Use `begin = &str[0];` instead of `begin = &str.front()` and `end = &str[str.size()]` instead of `end = &str.back()`. Also, change `ctype>` to `ctype >` (a space must go between the tokens). – David G Jun 27 '13 at 00:12
@0x499602D2 Haha im compiling on iOS using theos thats why my compiler is not updated. Also, thanks it worked! – Mike Jun 27 '13 at 00:21
@user664303 *What* is outputting strings? I'm outputting *integers* to standard output. – David G Jul 14 '15 at 17:22
My mistake. Comment deleted. – user664303 Jul 14 '15 at 23:37

Alexandru Barbarosie · Answer 2 · 2013-06-26T22:17:40.027

1

Use std::isdigit() to check whether a character is a digit. Until space is not reached, add stepwise to a separate string.
Then use std::stoi() to convert your string to an int.
Clear the content of the string using clear() method.
Go to first step

Repeat until the end of the base string is not reached.

edited Jun 26 '13 at 22:17

answered Jun 26 '13 at 22:04

Alexandru Barbarosie

2,952
3
24
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score 1 · Answer 3 · edited May 23 '17 at 12:25

First use string tokenizer

std::string text = "token, test   153 67 216";

char_separator<char> sep(", ");
tokenizer< char_separator<char> > tokens(text, sep);

Then, if you do not know exactly how many values you will get, you shouldn't use single variables a b c, but an array like int input[200], or better, a std::vector, which can adapt to the number of elements you read.

std::vector<int> values;
BOOST_FOREACH (const string& t, tokens) {
    int value;
    if (stringstream(t) >> value) //return false if conversion does not succeed
      values.push_back(value);
}

for (int i = 0; i < values.size(); i++)
  std::cout << values[i] << " ";
std::cout << std::endl;

You have to:

#include <string>
#include <vector>
#include <sstream>
#include <iostream> //std::cout
#include <boost/foreach.hpp>
#include <boost/tokenizer.hpp>
using boost::tokenizer;
using boost::separator;

By the way, if you are programming C++ you might want to avoid using printf, and prefer std::cout

score 0 · Answer 4 · answered Jul 01 '15 at 19:26

#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <iterator>
#include <vector>

int main() {
    using namespace std;
   int n=8,num[8];
    string sentence = "10 20 30 40 5 6 7 8";
    istringstream iss(sentence);

  vector<string> tokens;
copy(istream_iterator<string>(iss),
     istream_iterator<string>(),
     back_inserter(tokens));

     for(int i=0;i<n;i++){
     num[i]= atoi(tokens.at(i).c_str());
     }

     for(int i=0;i<n;i++){
     cout<<num[i];
     }

}

score 0 · Answer 5 · answered Jul 17 '17 at 11:30

0

To read a line of string and extract integer from it,

 getline(cin,str);
 stringstream stream(str);
 while(1)
  {
    stream>>int_var_arr[i];
    if(!stream)
          break;
    i++;
    }
   }

the integers are stored in int_var_arr[]

answered Jul 17 '17 at 11:30

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Read all integers from string c++

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