Create an array of char from string array

Question

(language : C++) I have this array:

 string myArray[] = {"Apple", "Ball", "Cat"};

Is it possible to store each element in the above array to a new array? Something like this.

  char word1[] = myArray[0];
  char word2[] = myArray[1];
  char word3[] = myArray[2];

I checked the above code, it would throw an error. How would I get this functionality? I cannot use two-dimensional array because I don't know the length of my word in my actual program. A file has the list of words, I would have to read it into the array and get the above string array.

So myArray would have the line of text from the file and you want individual arrays for each word you encounter in the line? Can you shed some light on the end goal for this process? — Forty3
– Forty3, Commented Mar 24, 2017 at 22:15
Do you want to copy the data or do you just want a more readable access? — Tomas
– Tomas, Commented Mar 24, 2017 at 22:36
Why do you need to use character arrays? See std::string::c_str(). Look at the difficulty you are going through. Stay with std::string. — Thomas Matthews
– Thomas Matthews, Commented Mar 24, 2017 at 23:18

Community · Accepted Answer · 2017-05-23 12:10:21Z

1

As per the example that you have posted, this is what you are looking for:

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

int main() {
    string myArray[] = {"Apple", "Ball", "Cat"};

    char test0[myArray[0].length()];
    strcpy(test0, myArray[0].c_str());
    char test1[myArray[1].length()];
    strcpy(test1, myArray[1].c_str());
    char test2[myArray[2].length()];
    strcpy(test2, myArray[2].c_str());

    int i=0;
    for(i=0; i<(sizeof(test0)/sizeof(*test0)); i++)
        cout<<test0[i]<<" ";
    cout<<"\n";
    for(i=0; i<(sizeof(test1)/sizeof(*test1)); i++)
        cout<<test1[i]<<" ";
    cout<<"\n";
    for(i=0; i<(sizeof(test2)/sizeof(*test2)); i++)
        cout<<test2[i]<<" ";
    cout<<"\n"; 

    return 0;
}

In the above code, I have created character arrays test0[], test1[] and test2[] of length equal to the corresponding string in myArray[]. Then I used strcpy() to copy the corresponding string from myArray[] to the character array (test0[], etc). Finally, I just printed these new character arrays.

Working code here.

Note: I am assuming that you are using GCC, since it supports VLAs. If not, then you can use an array of particular length (or better yet, a vector).

Hope this is helpful.

edited May 23, 2017 at 12:10

CommunityBot

11 silver badge

answered Mar 24, 2017 at 22:20

abhishek_naik

1,2952 gold badges15 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Miles Budnek Over a year ago

Standard C++ doesn't have VLAs, so char test[str0.length()]; is not valid code. Some compilers provide it as an extension, but it's not standard.

Thomas Matthews Over a year ago

My understanding is that declared arrays must have a compile-time constant as their capacity. Otherwise one must use the new operator and dynamically allocate the array.

Tyler Lewis · Accepted Answer · 2017-03-24 22:45:25Z

0

Old style (c++98/c++03):

#include <string>
#include <iostream>

int main()
{
    std::string myArray[] = { "Apple", "Ball", "Cat" };
    char *firstString = new char[myArray[0].length() + 1];
    char *secondString = new char[myArray[1].length() + 1];
    char *thirdString = new char[myArray[2].length() + 1];

    strcpy(firstString, myArray[0].c_str());
    strcpy(secondString, myArray[1].c_str());
    strcpy(thirdString, myArray[2].c_str());

    std::cout << "firstString = " << firstString << std::endl;
    std::cout << "secondString = " << secondString << std::endl;
    std::cout << "thirdString = " << thirdString << std::endl;

    delete firstString;
    delete secondString;
    delete thirdString;

    return 0;
}

New style (c++11/14):

#include <string>
#include <iostream>
#include <memory>

int main()
{
    std::string myArray[] = { "Apple", "Ball", "Cat" };
    std::unique_ptr<char> firstString{ new char[myArray[0].length() + 1] };
    std::unique_ptr<char> secondString{ new char[myArray[1].length() + 1]};
    std::unique_ptr<char> thirdString{ new char[myArray[2].length() + 1]};

    strcpy(firstString.get(), myArray[0].c_str());
    strcpy(secondString.get(), myArray[1].c_str());
    strcpy(thirdString.get(), myArray[2].c_str());

    std::cout << "firstString = " << firstString.get() << std::endl;
    std::cout << "secondString = " << secondString.get() << std::endl;
    std::cout << "thirdString = " << thirdString.get() << std::endl;

    return 0;
}

answered Mar 24, 2017 at 22:45

Tyler Lewis

8817 silver badges19 bronze badges

4 Comments

user6490375 Over a year ago

Would you please care to explain your C++11 approach? Like, why you are using a unique_ptr<>, the .get() method, etc.?

Tyler Lewis Over a year ago

Yeah, no problem. Basically, std::unique_ptr is a safer replacement whenever you have something that you must create on the heap/dynamically (using the new operator). When the destructor for std::unique_ptr is called (when it falls out of scope, etc), it will automatically delete the resource held, so you never have to worry about a memory leak by forgetting to use delete. However, a std::unique_ptr is not the exact same thing as a raw pointer, and for functions that expect a raw pointer, you can use the .get() method to return the underlying raw pointer to the object you created.

user6490375 Over a year ago

So, can I use unique_ptr<> majority of the times when I would require the new operator? Also, could you please point to some resources wherein I would learn about how to apply my C++11 knowledge? I know C++, but not C++11, since I didn't practice it. I would appreciate some resources to practice.

Tyler Lewis Over a year ago

Yes! That's exactly right. Idiomatic C++11 means you try to use new and delete as scarcely as possible. C++11 is really an entirely new language, it has so many good features. I learned all of my C++11/14 knowledge from Scott Meyer's "Effective Modern C++". It is of course excellent, but expect to read it a few times to grasp the concepts. I found it extremely terse, and so much high level information is packed into such a small book that you really have to take it slow. In regards to truly using it, rewrite old projects using as much c++11 as you can, and apply the concepts from that book.

Collectives™ on Stack Overflow

Create an array of char from string array

2 Answers 2

2 Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related