How to Initialize a Point Array?

Question

I am writing some Win32 program. and I meet a problem. I define an array of Point,just like this:

   POINT points[3];

and now I want to Initialize it, and I know this is illegal

   POINT points[3] = { (295,295),(200,200),(400,500) };

so I need the correct way.

You don't really need the 3. Just let the computer do the counting for you. — cup
– cup, Commented Dec 18, 2013 at 21:48
@user3116182: Illegal? It doesn't do what you apparently want it to do, but it is certainly not illegal. The code will compile. — AnT stands with Russia
– AnT stands with Russia, Commented Dec 19, 2013 at 0:30

AnT stands with Russia · Accepted Answer · 2013-12-19 00:29:24Z

2

You can do it simply as

POINT points[3] = { 295, 295, 200, 200, 400, 500 };

but a safer thing to do would be this

POINT points[3] = { { 295, 295 }, { 200, 200 }, { 400, 500 } };

The amusing part is that what you originally wrote is not illegal (where did you get that idea?). The () you used inside your initializer will cause the inner , to be interpreted as comma operator. For example, expression (400, 500) evaluates to 500. That means that your original initializer is actually treated as

POINT points[3] = { 295, 200, 500 };

which is in turn equivalent to

POINT points[3] = { { 295, 200 }, { 500, 0 }, { 0, 0 } };

It doesn't do what you want it to do, but it is certainly not illegal.

edited Dec 19, 2013 at 0:29

answered Dec 18, 2013 at 21:57

AnT stands with Russia

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3 Comments

user3116182 Over a year ago

nice answer. I am sorry that my expression is not rigorous.

user3116182 Over a year ago

Can you tell me more about inner comma operator, such as its source code. @AndreyT

AnT stands with Russia Over a year ago

@user3116182: Comma operator in your original code case is a built-in operator, part of core C++ language. It has no "source code". There's plenty of info about it on the Net (en.wikipedia.org/wiki/Comma_operator).

David · Accepted Answer · 2013-12-18 21:53:52Z

0

As per the comments:

POINT points[] = {{295,295}, {200,200}, {400,500}};

answered Dec 18, 2013 at 21:53

David

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