Combining a vector of strings

user_178481 0
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I've been reading Accelerated C++ and I have to say it's an interesting book.

In chapter 6, I have to use a function from <algorithm> to concatenate from a vector<string> into a single string. I could use accumulate, but it doesn't help because string containers can only push_back characters. 

int main () {
  using namespace std;
  string str = "Hello, world!";
  vector<string>  vec (10, str);
  // Concatenate here?

  return 0;
}

How do I join the strings together?

vector stl c++ string
5 Answers

Assuming this is question 6.8, it doesn't say you have to use accumulate - it says use "a library algorithm". However, you can use accumulate:

#include <numeric>
    
int main () {
    std::string str = "Hello World!";
    std::vector<std::string> vec(10,str);
    std::string a = std::accumulate(vec.begin(), vec.end(), std::string(""));
    std::cout << a << std::endl;
}

All that accumulate does is set 'sum' to the third parameter, and then for all of the values 'val' from first parameter to second parameter, do:

sum = sum + val

it then returns 'sum'. Despite the fact that accumulate is declared in <numeric> it will work for anything that implements operator+()

Note: This solution, while elegant, is inefficient, as a new string will be allocated and populated for each element of vec.

Admin1

How about std::copy?

std::ostringstream os;
std::copy( vec_strings.begin(), vec_string.end(), ostream_iterator<string>( os ) );
cout << os.str() << endl;
Sanjaya_R_93530

I am not sure about your question.Where lies the problem? Its just a matter of a loop.

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

int main () 
{
    std::string str = "Hello World!";
    std::vector<string>  vec (10,str);

    for(size_t i=0;i!=vec.size();++i)
        str=str+vec[i];
    std::cout<<str;
}

EDIT :

Use for_each() from <algorithm>

Try this:

#include<vector>
#include<string>
#include<iostream>
#include<algorithm>
using namespace std;
string i;
void func(string &k)
{
  i+=k;
}
int main () {
    string str = "Hello World!";
    vector<string>  vec (10,str);

    for_each(vec.begin(),vec.end(),func);
    cout<<i;
    return 0;
  }
user_1655200

This answer is an improved version of the one from @PrasoonSaurav by adding a helpful sep argument.

inline std::string joinStrings(std::vector<std::string> arr, std::string sep) {
    std::string out = arr[0];
    for(unsigned int i = 1; i < arr.size(); i++) {
        out += sep + arr[i];
    }
    return out;
}

// Overload function parameter to add default value for the separator
inline std::string joinStrings(std::vector<std::string> arr) {
    return joinStrings(arr, std::string(", "));
}
user_23138890
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