Struct Initialization

[Travis]

struct Point
{
int x;
int y;
};

Point Lines[3] =
{
{0,1},
{1,2},
{2,3}
}
The above works fine. What I'd like to do is declare Lines first and
then populate the array later without having to individually add .x =
and .y= for every attribute.

Point Lines[3];

Lines[0] = {0,1};

This doesn't work. Is there someway to do that though without

Point Lines[3];
Lines[0].x=0;
Lines[0].y=1;

Thanks

[Victor Bazarov]

Travis wrote:

struct Point
{
int x;
int y;
};

Point Lines[3] =
{
{0,1},
{1,2},
{2,3}
}
The above works fine. What I'd like to do is declare Lines first and
then populate the array later without having to individually add .x =
and .y= for every attribute.

Point Lines[3];

Lines[0] = {0,1};

This doesn't work. Is there someway to do that though without

Point Lines[3];
Lines[0].x=0;
Lines[0].y=1;

No. There are no "aggregate literals" in C++ yet. You can, of course
create a pseudo-constructor (or a "factory function"):

Point createPoint(int x, int y) {
Point p = { x, y };
return p;
}

and then do

Lines[0] = createPoint(0,1);
Lines[1] = createPoint(1,2);

etc.

V
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[Mike Wahler]

"Travis" <tr***********@gmail.comwrote in message
news:d7**********************************@25g2000h sx.googlegroups.com...

struct Point
{
int x;
int y;
};

Point Lines[3] =
{
{0,1},
{1,2},
{2,3}
}
The above works fine. What I'd like to do is declare Lines first and
then populate the array later without having to individually add .x =
and .y= for every attribute.

Point Lines[3];

Lines[0] = {0,1};

This doesn't work. Is there someway to do that though without

Point Lines[3];
Lines[0].x=0;
Lines[0].y=1;

Thanks

struct Point
{
int x;
int y;
public:
Point(int xx = 0, int yy = 0) : x(xx), y(yy) { }
};

int main()
{
Point Lines[3];
Lines[0] = Point(0, 1);
Lines[1] = Point(1, 2);
Lines[2] = Point(2, 3);
return 0;
}
-Mike

[Eric Pruneau]

"Travis" <tr***********@gmail.coma écrit dans le message de news:
d7**********************************...oglegroups.com...

struct Point
{
int x;
int y;
};

Point Lines[3] =
{
{0,1},
{1,2},
{2,3}
}
The above works fine. What I'd like to do is declare Lines first and
then populate the array later without having to individually add .x =
and .y= for every attribute.

Point Lines[3];

Lines[0] = {0,1};

This doesn't work. Is there someway to do that though without

Point Lines[3];
Lines[0].x=0;
Lines[0].y=1;

Thanks

No but you can add a SetPoint function

struct Point
{
int x;
int y;
void SetPoint(int NewX, int NewY) { x=NewX; y = NewY; }
}
Point Lines[3];
Lines[0].SetPoint(0,1);

-----------------------

Eric Pruneau

[Rolf Magnus]

Victor Bazarov wrote:

>Point Lines[3];

Lines[0] = {0,1};

This doesn't work. Is there someway to do that though without

Point Lines[3];
Lines[0].x=0;
Lines[0].y=1;

No. There are no "aggregate literals" in C++ yet. You can, of course
create a pseudo-constructor (or a "factory function"):

Point createPoint(int x, int y) {
Point p = { x, y };
return p;
}

and then do

Lines[0] = createPoint(0,1);
Lines[1] = createPoint(1,2);

Or simply a regular constructor (if the struct doesn't have to be POD).

[Travis]

So I'm not sure what I'm missing.

Here's my test http://paste.cbwhiz.com/281

If I uncomment line 27 and comment out 28-30, everything works.

As it is though, I get a link error (I believe) that says : undefined
reference to `Point::Point[in-charge]()'

Also, I have tried class and struct, both produce the same results.

[Victor Bazarov]

Travis wrote:

So I'm not sure what I'm missing.

Here's my test http://paste.cbwhiz.com/281

If I uncomment line 27 and comment out 28-30, everything works.

As it is though, I get a link error (I believe) that says : undefined
reference to `Point::Point[in-charge]()'

Also, I have tried class and struct, both produce the same results.

You declared the default c-tor in 'Point', but never defined it. When
you define an array of Point and provide no initialisers, the default
c-tor is *used*. Since no definition exists, the linker cannot find the
function. Change the constructors from

Point();
Point(int x_, int y_) : x(x_), y(y_) { }

to
explicit Point(int x_ = 0, int y_ = 0) : x(x_), y(y_) { }

(thus making your constructor both parameterised AND default).
V
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[Travis]

On Jul 14, 1:34*pm, Victor Bazarov <[e-mail]:

Travis wrote:

So I'm not sure what I'm missing.

Here's my testhttp://paste.cbwhiz.com/281

If I uncomment line 27 and comment out 28-30, everything works.

As it is though, I get a link error (I believe) that says : undefined
reference to `Point::Point[in-charge]()'

Also, I have tried class and struct, both produce the same results.

You declared the default c-tor in 'Point', but never defined it. *When
you define an array of Point and provide no initialisers, the default
c-tor is *used*. *Since no definition exists, the linker cannot find the
function. *Change the constructors from

* * * * *Point();
* * * * *Point(int x_, int y_) : x(x_), y(y_) { }

to
* * * * *explicit Point(int x_ = 0, int y_ = 0) : x(x_), y(y_) { }

(thus making your constructor both parameterised AND default).

V
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Ah ha. Fantastic. Thank you very much. Sometimes another pair of eyes
is worth millions.

Thanks again

[Victor Bazarov]

Travis wrote:

[..] Sometimes another pair of eyes
is worth millions.

:-) If I had a nickel every time I heard that...

You're welcome!

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask