CODEWITHSUNDEEP
c++
Muhammad Hassan
Muhammad Hassan

Reputation: 11

Simple assignment of characters from one string to other is not working

I am trying to assign characters from one string to other using function but I am getting error.

"terminate called after throwing an instance of 'std::out_of_range' what(): basic_string::at: __n (which is 0) >= this->size() (which is 0)"

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

void split (std::string line)
{
    std::string::size_type leng=0;
    leng=line.length();
    std::string k;

    for (long unsigned int i=0;i<leng; i++)
    {
        k.at(i)=line.at(i);
    }

    std::cout<<k;
}

int main()
{
    std::string line = "";
    std::cout << "Enter a string: ";
    getline(std::cin, line);
    split(line);
}

Upvotes: 1

Views: 138

Answers (4)

Agustin Durand
Agustin Durand

Reputation: 11

You are trying to access an element of an empty string, please use this code.

#include <iostream>
#include <string>

void split (const std::string& line) // pass parameter by reference to avoid copy
{
    std::string::size_type leng = line.length();
    std::string k;
    k.resize(leng); // use resize to create space for the new characters

    for (long unsigned int i = 0; i < leng; i++)
    {
        k.at(i)=line.at(i);
    }

    std::cout << k;
}

int main()
{
    std::string line = "";
    std::cout << "Enter a string: ";
    getline(std::cin, line);
    split(line);
}

Upvotes: 0

sweenish
sweenish

Reputation: 5202

#include <iostream>
#include <string>

void split (std::string line)
{
    std::string::size_type leng = line.length();
    std::string k;

    for (long unsigned int i = 0; i < leng; i++)
    {
        k.push_back(line.at(i));  // This is the only real change
    }

    std::cout << k;
}


int main()
{
    std::string line = "";
    std::cout << "Enter a string: ";
    getline(std::cin, line);
    split(line);
}

When k is declared, it is empty. It's size is therefore 0. You are using the .at() function, which accesses a specific element (character) and throws an exception when you go out of bounds. You immediately go out of bounds because k is empty.

Now, your function doesn't split (yet, or you left that part out), but .push_back() seems like it will fit what you're trying to do best. It will add the characters to the end of the string, and grow the string as needed; you won't have to worry about manually managing its size.

Upvotes: 1

Reza Mahdi
Reza Mahdi

Reputation: 98

This exception is thrown because any new string that is created whitout initial content, have 0 len. Accessing characters via at() expect that index have a character, but the k have no no value even at 0.

You can resize the string first, and then use at()

std::string k;
k.resize(leng);

Upvotes: 1

Lukas-T
Lukas-T

Reputation: 11340

When you initialize k it is an emtpy string. So k.at(i) will be out of of bounds as the error message says.

There are plenty of ways to copy a string, you could use a constructor like std::string k(line); or k.assign(line) or you could use resize() to resize k before the loop.

Upvotes: 4

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