How to transform a vector into a string?

Question

I am trying to pass a value from C++ to TCL. As I cannot pass pointers without the use of some complicated modules, I was thinking of converting a vector to a char array and then passing this as a null terminated string (which is relatively easy).

I have a vector as follows:

12, 32, 42, 84

which I want to convert into something like:

"12 32 42 48"

The approach I am thinking of is to use an iterator to iterate through the vector and then convert each integer into its string representation and then add it into a char array (which is dynamically created initially by passing the size of the vector). Is this the right way or is there a function that already does this?

Wow, me too. Exactly this scenario! – Andy Dent Nov 30 '11 at 23:49 — Andy Dent, Nov 30 '11 at 23:49

score 62 · Accepted Answer · answered Mar 25 '10 at 20:12

62

What about:

std::stringstream result;
std::copy(my_vector.begin(), my_vector.end(), std::ostream_iterator<int>(result, " "));

Then you can pass the pointer from result.str().c_str()

answered Mar 25 '10 at 20:12

fbrereto

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This will not include the spaces, will it? – Jon Benedicto Mar 25 '10 at 20:13
The space is passed to the iterator, so they will be included. – stefaanv Mar 25 '10 at 20:17
4

Sir, I will never ever again forget about ostream_iterator and copy. Thank you. – Björn Pollex Mar 25 '10 at 20:19
4

@Adrian McCarthy: You don't need to `#include ` or `` for this example code. `` contains the needed definitions. You do need ``, `` and ``. – Billy ONeal Mar 25 '10 at 20:48
2

How do you avoid the trailing space? – avakar Mar 25 '10 at 20:54
Thanks for the approach! – Legend Mar 25 '10 at 22:31
1

You can use `string::erase` to remove the trailing space afterwards. – Björn Pollex Mar 26 '10 at 08:47
3

@BillyONeal: You're probably right in ``, but you need `` for `std::ostream_iterator`. – Adrian McCarthy Mar 26 '10 at 15:45
@Adrian McCarthy: Doh! Open mouth insert foot Bill! :) You are correct sir! – Billy ONeal Mar 26 '10 at 15:53
How to get a big number instead of string i.e instead of "12 32 42 48" 12324248? – nbbk Dec 31 '13 at 08:38
@BillyONeal Thank you for telling us which libraries are needed to be included. I hate it when the user that answers does not provide that information, does give me a hard time, and many other users too, I believe. – Silidrone Oct 08 '18 at 15:20

score 7 · Answer 2 · answered Mar 25 '10 at 20:15

7

You can use copy in conjunction with a stringstream object and the ostream_iterator adaptor:

#include <iostream>

#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> v;
    v.push_back(12);
    v.push_back(32);
    v.push_back(42);
    v.push_back(84);

    stringstream ss;
    copy( v.begin(), v.end(), ostream_iterator<int>(ss, " "));
    string s = ss.str();
    s = s.substr(0, s.length()-1);  // get rid of the trailing space

cout << "'" << s << "'";

    return 0;
}

Output is:

'12 32 42 84'

answered Mar 25 '10 at 20:15

John Dibling

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Thanks for trailing space removal... – Legend Mar 25 '10 at 22:33
1

In case your having issue with VS2015 on using ostream_iterator, include as header file. – Akshay Apr 08 '17 at 09:03

score 4 · Answer 3 · answered Mar 25 '10 at 20:13

4

I'd use a stringstream to build the string. Something like:

std::vector<int>::const_iterator it;
std::stringstream s;
for( it = vec.begin(); it != vec.end(); ++it )
{
    if( it != vec.begin() )
        s << " ";

    s << *it;
}

// Now use s.str().c_str() to get the null-terminated char pointer.

answered Mar 25 '10 at 20:13

Jon Benedicto

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+1 for avoiding the trailing space of my suggestion. – Björn Pollex Mar 25 '10 at 20:15
At expense of extra comparisons if( it != vec.begin() ). – Viet Mar 26 '10 at 10:18

score 2 · Answer 4 · answered Mar 25 '10 at 20:11

You got it right, but you can use std::ostringstream to create your char array.

#include <sstream>

std::ostringstream StringRepresentation;
for ( vector<int>::iterator it = MyVector.begin(); it != MyVector.end(); it++ ) {
    StringRepresentation << *it << " ";
}

const char * CharArray = StringRepresentation.str().c_str();

In this case, CharArray is only for reading. If you want to modify the values, you will have to copy it. You can simplify this by using Boost.Foreach.

How to transform a vector into a string?

4 Answers4

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