Read all integers from string c++

问题

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!

回答1:

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

回答2:

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.

回答3:

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

回答4:

#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];
     }

}

回答5:

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[]

来源：https://stackoverflow.com/questions/17331250/read-all-integers-from-string-c

标签

c++

string

integer