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Confusion with structs

Started by antistuff Jan 4, 2003 at 11:10 PM 2 replies 450+ views

Original Post

Jan 4, 2003 at 11:10 PM

Im using c, not c++. So i have a struct like this typedef struct { int a; int b; } foo; now i have this foo f1, f2; f1.a = 1; f1.b = 2; if i go like this f2 = f1; is it the same as doing this f2.a = f1.a f2.b = f1.b i would think it is, but it seems like f2 = f1 makes f2 point to f1. but f2 isnt a pointer. which behavior is right? does it copy the values, or somethign else?

Fruny

203

Fruny

Jan 4, 2003 at 11:16 PM

f2 = f1;

is indeed exactly the same as

f2.a = f1.a
f2.b = f1.b

unless you have written a custom assignment operator.

johnnie2

Jan 4, 2003 at 11:18 PM

It''s a copy.

If you haven''t explicitly provided a copy constructor for that struct (which you can do, btw), the compiler automatically comes up with one. In this case, the members of the first struct would be copied to the members of the second struct.

RapscallionGL - arriving soon.

spock

Jan 5, 2003 at 4:23 AM

quote:
Original post by johnnie2
If you haven''t explicitly provided a copy constructor for that struct (which you can do, btw)

No, not in C you can''t.

Struct assignment and memberwise assignment may not be exactly equivalent due to the possibility of padding between structure members. The former may copy everything including padding while memberwise assignment will never copy padding.

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