CODEWITHSUNDEEP
c++carraysdynamicmalloc
ParoX
ParoX

Reputation: 5933

Dynamic and continuous array

Is there anyway to make a 1D dynamic and continuous array using C++11?

I will take in the size of the array via stdin and once it's created it won't need to be resized.

Right now I am using a 1D vector of enums, and my biggest performance issue is the vector [] operator.

If it can't be done in C++, I am open to ways of doing it with malloc and C, just please note the best way to delete it.

Edit: Didn't realize vectors were night and day with debug and release. I reran callgrind with -O3 and now the issue is ostream not vectors - thanks to everyone who made me second guess myself before I rewrote it all using arrays when not needed.

Upvotes: 0

Views: 557

Answers (5)

Paul Draper
Paul Draper

Reputation: 83283

If you are using C++, using malloc is probably a poor (inferior) idea.

int length;
cin >> length;

MyType * array = new MyType[length];

Then to delete,

delete[] MyType;

Upvotes: 0

rAndom69
rAndom69

Reputation: 765

    int size = 10;
    std::unique_ptr<int[]>  a(new int[size]);

Follows RAII (that is array is autodestructed) However I don't think vector [] operator should be performance issue. In debug compilation it may be checked, however in release it should not.

In MSVC there is feature called checked iterators which may "kill" performance. However you're able to switch this feature off (just google it)

Upvotes: 3

George Sovetov
George Sovetov

Reputation: 5238

std::vector has enough performance to use in production. It is used for solving problems on programming contests. Maybe, you forget to compile into release?

Also, you can use new and delete operators.

To free allocated memory use free(void *ptr) function.

Upvotes: 2

Abhijit
Abhijit

Reputation: 63737

You can always dynamically create contiguous homogeneous storage of a certain type from the heap using the new operator 

Type *pType = new Type[size](initial_value)

In Order to delete the storage, you need to explicitly invoke the array delete operator

delete[] pType

But, when you say, and my biggest performance issue is the vector [] operator., I doubt. Did you profile the retail version of your code? How do you know the vector subscript is your performance bottleneck?

Upvotes: 3

Floris
Floris

Reputation: 46405

In C you create a 1-D array with

int *ptr=NULL;
int num_elements = 0;
printf("how many elements?\n");
if(scanf("%d", &num_elements)==1) {
  ptr = malloc(sizeof(int)*num_elements);
  if(ptr == NULL) {
    printf("unable to allocate %d elements\n", num_elements);
    exit 0;
  }
}

and when you're done, you call

free(ptr);

Make sure you call it only once! Some people will do 

if( ptr != NULL ) {
  free(ptr);
  ptr = NULL;
}

as defensive coding - prevents accidentally freeing it twice.

Upvotes: 0

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