Set all values of an existing array to "magic numbers"

Question

So I know that I can set each value of an array to a "magic number" (in this case a magic string) at the time of construction like;

string * myArray[] = {"foo", "bar", "baz"};

What would be useful is if I could declare my array;

string * myArray[100];

Then later (in an if statement) set its values;

myArray = {"foo", "bar", "baz"};

(the actual array will contain ~30 magic strings, so I don't want to assign them all one at a time)

I understand that magic numbers (or magic strings) are not good. However the system I am working in is CERN's root, which is full of interesting eccentricities, and I would rather not to lose any more time searching for a neater approach. So in the interest of not letting perfect become the enemy of the good I am going to use magic numbers.

What's the quickest option here?

Edit; The accepted answer works great for c++11. If, like me, you don't have that option, here is a very-nasty-but-functional solution. (Programmers with sensibilities please shield your eyes.)

int numElements;
vector<char *> myArray;
if(someCondition){
  numElements = 3;
  string * tempArray[] = {"foo", "bar", "baz"}]
  for(int n = 0; n < numElements; n++){
    const char * element = (tempArray[n]);
    myArray.push_back(element);
  }
}else if(anoutherCondition){
//More stuff
}

Could do, but does that help? We still cant set like `={"foo", "bar", "baz"}` I think? — Jekowl, Aug 07 '15 at 15:31
@NathanOliver Loop over all the branches in a tree (by name) — Jekowl, Aug 07 '15 at 15:33
That doesn't compile did you mean `std::string myArray[] = {"foo", "bar", "baz"};`? — Galik, Aug 07 '15 at 15:35
Then skip using an array and use a [`std::vector`](http://en.cppreference.com/w/cpp/container/vector). It has a function called `push_back()` that you can use to add elements to it during run-time and it will automatically expand to handle as many elements as you need. — NathanOliver, Aug 07 '15 at 15:35
@Giorgi because that was working when I had only one option (didn't need the if statement) is it bad style? — Jekowl, Aug 07 '15 at 15:35
@NathanOliver Yes but then I have do them one at a time and I might as well do `myArray[n] = "foo"` — Jekowl, Aug 07 '15 at 15:36
Please use `std::array` if you want a static array, or `std::vector` if you want a dynamic array. There's no use for raw arrays in C++ anymore. — Emil Laine, Aug 07 '15 at 15:41

score 3 · Accepted Answer · answered Aug 07 '15 at 15:37

3

Although built-in arrays do not allow aggregate assignments, std::vector lets you do this:

vector<string> data;
if (someCondition) {
    data = {"quick", "brown", "fox"};
} else {
    data = {"jumps", "over", "the", "lazy", "dog"};
}

Demo.

This approach has several advantages:

The syntax is compact and intuitive
Assigned aggregates are allowed to have different length
Resources allocated to std::vector are freed automatically.

answered Aug 07 '15 at 15:37

Sergey Kalinichenko

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I receive an error from this - its long though so its in the bottom of the question. – Jekowl Aug 07 '15 at 15:45
@Jekowl You need to compile as (at least) C++11. – Emil Laine Aug 07 '15 at 15:47
@Jekowl This syntax is available in C++11 and C++14, so you may need to turn on a special flag in your compiler (assuming that your compiler supports C++11 or higher). – Sergey Kalinichenko Aug 07 '15 at 15:48
@zenith ah, that may not be possible. I will leave this question open for a bit longer, to see if any alternatives are suggested, then accept this answer for the benefit of future readers. – Jekowl Aug 07 '15 at 15:48
Can you use the ternary (?:) operator to replace the assignment with a construction? – KABoissonneault Aug 07 '15 at 16:29
@KABoissonneault Yes, but the syntax is a little different ([demo](http://ideone.com/7mh9w3)). – Sergey Kalinichenko Aug 07 '15 at 16:37
@dasblinkenlight Alright, it doesn't seem worth it in that case since it's going to end up as an assignment anyway – KABoissonneault Aug 07 '15 at 16:38

score 2 · Answer 2 · answered Aug 07 '15 at 15:41

I think you probably mean an array of std::string rather than an array of std::string* like this:

std::string myArray[] = {"foo", "bar", "baz"};

The way I would do this is to allow a std::vector to manage the array for me. That allows me to easily copy, move or swap new values in later:

std::vector<std::string> myVector = {"foo", "bar", "baz"};

myVector = {"wdd", "ghh", "yhh"};

Set all values of an existing array to "magic numbers"

2 Answers2