C++ assign element of a string to a new string

Question

Im trying to assign a piece of a string, to a new string variable. Now Im pretty new so longer, but easier to understand explanations are the best for me. Anyways, how Im trying to do it is like this:

string test = "384239572";
string u = test[4];

The full code of what im trying to do is this:

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

int main()
{
string test = "384239572";
string u = test[4];
int i = 0;
istringstream sin(u);
sin >> i;
cout << i << endl;
return 0;
}

Though it seems to complain at the upper part that I put up there. So how can I take a small part of a string from a string, and assign it to a new string? Thanks a lot in advance! If you know any good links or anything about this, that would be appreciated too!

jcpennypincher · Accepted Answer · 2011-06-01 04:03:31Z

4

use substring,

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

int main()
{
    string test = "384239572";
    string u = test.substr(4,1);
    cout << u << endl;
    return 0;
}

answered Jun 1, 2011 at 4:03

jcpennypincher

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GWW · Accepted Answer · 2011-06-01 03:59:54Z

3

You can use one of the string constructors

string u(1,test[4]);

EDIT: The 1 indicates the number of times to repeat the character test[4]

In your code you are trying to assign a char to a string object.

answered Jun 1, 2011 at 3:59

GWW

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5 Comments

samuraiseoul Over a year ago

Okay, thanks, what does the 1 in this do though? Also can you maybe explain to me why my method doesn't work? That way I can have maximum understanding for future reference? :D

cgmb Over a year ago

It's in the constructor documentation he linked: string ( size_t n, char c ); Content is initialized as a string formed by a repetition of character c, n times.

samuraiseoul Over a year ago

So when I use test[] it becomes a char and is no longer a string?

samuraiseoul Over a year ago

Also I noticed that when I do string u; u = test[1]; It works, but if I try to do it in one line it won't. Why is that?

GWW Over a year ago

The string assignment operator is overloaded to support assinging a char to a string.

Ernest Friedman-Hill · Accepted Answer · 2011-06-01 04:03:18Z

2

The string class has a method substr() that would be useful here:

// Substring consisting of 1 character starting at 0-based index 4
string u = test.substr(4, 1);

This generalizes nicely to substrings of any length.

answered Jun 1, 2011 at 4:03

Ernest Friedman-Hill

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