If I have:
struct a_struct
{
int an_int;
a_struct(int f) : an_int(f) {}
a_struct() : an_int(0) {}
};
class a_class
{
a_struct * my_structs;
a_class() {...}
};
I can do:
a_class() {my_structs = new a_struct(1)}
//or
a_class() {my_structs = new a_struct [10]}
But I cannot do:
a_class() {my_structs = new a_struct(1) [10]}
//or
a_class() {my_structs = new a_struct() [10]}
Is there any correct syntax to get this to work? Or an easy work around?
If using the STL is an option, you could use std::vector instead of a dynamic array.
I think that this will work:
std::vector<a_struct> my_structs;
my_structs.assign(10, 1);
If not, this should:
my_structs.assign(10, a_struct(1));
std::vector<a_struct> my_structs(10, 1);You could allocate a raw chunk of memory and use placement new to initialize each struct:
int number_of_structs = 10;
my_structs = (a_struct*)new unsigned char[sizeof(a_struct) * number_of_structs];
// allocate a raw chunk of memory
a_struct* p = m_structs;
for (int i=0; i<number_of_structs; i++)
{
new (p) a_struct(i);
p++;
}
//When done should add code for deallocation to help people
// to understand the full cycle of memory management.
for (auto i=0; i<number_of_structs; ++i) {
my_structs[i].~a_struct();
}
delete[] my_structs;
See also: What uses are there for "placement new"?
You could use an array of pointers to pointers. Then you can create the array that will hold pointers to a_struct(), so you can decide later which constructor to use:
class a_class {
a_struct ** my_structs;
a_class() { my_structs = new a_struct* [10]}
void foo () {
my_structs[0] = new a_struct(1);
my_structs[5] = new a_struct("some string and float constructor", 3.14);
}
};
You can't do it directly on any particular parameterized constructor. However you can do,
a_struct *my_struct[10] = {}; // create an array of pointers
for (int i = 0; i < 10; i++)
my_struct[i] = new a_struct(i); // allocate using non-default constructor
I suggest using a std::vector container instead of going through this process.
