How do I convert vector of strings into vector of integers in C++?

Question

I have a vector of strings. Need help figuring out how to convert it into vector of integers in order to be able to work with it arithmetically. Thanks!

#include         


        

Answer 1

There are two independent tasks.

1. Convert a single string to an integer
2. Having something that can convert from A to B, convert std::vector<A> to std::vector<B>

I suggest you try to do them separately, and then combine the results. If one of these tasks proves difficult, you will be able to ask a more focused question.

Answer 2

Use boost::lexical_cast. And surround it with try-catch block.

try
{
   for (size_t i=0; i<vectorOfStrings.size(); i++)
   {
      vectorOfIntegers.push_back(boost::lexical_cast<int>(vectorOfStrings[i]));
   }
}
catch(const boost::bad_lexical_cast &)
{
    //not an integer 
}

---

Or you can use Boost.Spirit parser (which someone claims is faster than even atoi()) as:

int get_int(const std::string & s)
{
    int value = 0;
    std::string::const_iterator first = s.begin();
    bool r = phrase_parse(first,s.end(),*int_[ref(value)=_1], space);
    if ( !r || first != s.end()) throw "error"; 
    return value;
}

//Usage
int value = get_int("17823");
std::cout << value << std::endl; //prints 17823

The full demo using your code : http://ideone.com/DddL7

Answer 3

There are mulitple ways of converting a string to an int.

Solution 1: Using Legacy C functionality

int main()
{
    //char hello[5];     
    //hello = "12345";   --->This wont compile

    char hello[] = "12345";

    Printf("My number is: %d", atoi(hello)); 

    return 0;
}

Solution 2: Using lexical_cast(Most Appropriate & simplest)

int x = boost::lexical_cast<int>("12345"); 

Surround by try-catch to catch exceptions.

Solution 3: Using C++ Streams

std::string hello("123"); 
std::stringstream str(hello); 
int x;  
str >> x;  
if (!str) 
{      
   // The conversion failed.      
} 

Answer 4

Here is the working version made up using the above comments.

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

using namespace std;

int main(int argc, char* argv[]) {

    vector<string> vectorOfStrings;
    vectorOfStrings.push_back("1");
    vectorOfStrings.push_back("2");
    vectorOfStrings.push_back("3");

    for (int i=0; i<vectorOfStrings.size(); i++)
    {
        cout<<vectorOfStrings.at(i)<<endl;
    }

    vector<int> vectorOfIntegers;
    int x;
    for (int i=0; i<vectorOfStrings.size(); i++)
    {
        stringstream str(vectorOfStrings.at(i));
        str >> x;
        vectorOfIntegers.push_back(x);
    }

    int sum = 0;
    for (int i=0; i<vectorOfIntegers.size(); i++)
    {
        sum += vectorOfIntegers.at(i);
    }
    cout<<sum<<endl;
    cin.get();

    return 0;
}

Answer 5

#include <string>
#include <vector>

#include <iterator>
#include <algorithm>
#include <boost/lexical_cast.hpp>

using namespace std;

int stringToInteger(const std::string& s)
{
    return boost::lexical_cast<int>(s);
}

int main(int /*argc*/, char* /*argv*/[])
{
    vector<string> vectorOfStrings;

    // ..

    vector<int> vectorOfIntegers;
    std::transform(vectorOfStrings.begin(), vectorOfStrings.end(), std::back_inserter(vectorOfIntegers), stringToInteger);

    // ..
}

You can replace the implementation of stringToInteger(..) with your preferred conversion function.

Answer 6

What about:

#include <algorithm>
#include <boost/lexical_cast.hpp>

template<typename C1, typename C2>
void castContainer(const C1& source, C2& destination)
{
    typedef typename C1::value_type source_type;
    typedef typename C2::value_type destination_type;
    destination.resize(source.size());
    std::transform(source.begin(), source.end(), destination.begin(), boost::lexical_cast<destination_type, source_type>);
}

It can convert vector<string> into vector<int>, and also other container<T1> into container2<T2>, e.g.: list -> list.

Full code:

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <string>
#include <boost/lexical_cast.hpp>

template<typename C1, typename C2>
void castContainer(const C1& source, C2& destination)
{
    typedef typename C1::value_type source_type;
    typedef typename C2::value_type destination_type;
    destination.resize(source.size());
    std::transform(source.begin(), source.end(), destination.begin(), boost::lexical_cast<destination_type, source_type>);
}

template<typename T, typename T2>
std::vector<T>& operator<<(std::vector<T>& v, T2 t)
{
    v.push_back(T(t));
    return v;
}

main(int argc, char *argv[])
{   
    std::vector<std::string> v1;
    v1 << "11" << "22" << "33" << "44";
    std::cout << "vector<string>: ";
    std::copy(v1.begin(), v1.end(), std::ostream_iterator<std::string>(std::cout, ", "));
    std::cout << std::endl;

    std::vector<int> v2;
    castContainer(v1, v2);

    std::cout << "vector<int>: ";
    std::copy(v2.begin(), v2.end(), std::ostream_iterator<int>(std::cout, ", "));
    std::cout << std::endl;
}