CODEWITHSUNDEEP
c++arrays
Diabl0658
Diabl0658

Reputation: 41

Filling a dynamic array c++

I have a struct with pointers to floats that i want to turn into an array of an indeterminate size. At the beginning of my program I want to declare a few of these structs and turn them into different sized arrays, like this:

struct _arr {
   float * a;
}

...

_arr x;
x.a = (float *)malloc(sizeof(float)*31);
x.a = { 6,
        1, 1, 1, 0     , 0     ,
        1, 0, 1, 0     , 0.0625,
        1, 1, 0, 0.0625, 0     ,
        1, 0, 1, 0     , 0.0625,
        1, 0, 0, 0.0625, 0.0625,
        1, 1, 0, 0.0625, 0
      };

Unfortunately this doesn't work, does anyone have any suggestions get the values into the array besides adding in each value in individually (such as a[0] = 6;)?

Upvotes: 0

Views: 1100

Answers (3)

juanchopanza
juanchopanza

Reputation: 227390

This could be simplified by storing a std::vector<float>:

#include <vector>

struct arr_ {
   std::vector<float> a;
};

In C++11, the initialization is trivial:

arr_ x{ {1.0f, 2.0f, 3.0f, 4.0f, 5.0f} };

Unfortunately, there is no trivial way to perform such an initialization in C++03. One option would be to initialize from a temporary fixed size array:

float farray_[5] = {1.0f, 2.0f, 3.0f, 4.0f, 5.0f};
arr_ x{ std::vector<float>(farray_, farray_+5)};

Upvotes: 3

beyrem
beyrem

Reputation: 436

x.a is a pointer and when you change x.a = xx you change the address

try this code:

x.a = new float( 6, 1, 1, 1, 0 , 0 , 1, 0, 1, 0 , 0.0625, 1, 1, 0, 0.0625, 0 , 1, 0, 1, 0 , 0.0625, 1, 0, 0, 0.0625, 0.0625, 1, 1, 0, 0.0625, 0 ) ;

Upvotes: 0

Karthik T
Karthik T

Reputation: 31952

You can initialize an array on the stack and then copy/memcpy to your dynamic memory. But using vector as suggested would be the better choice.

Upvotes: 1

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