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C++ Structs and Array question

Started by Hungry Joe Jan 8, 2003 at 1:51 PM 5 replies 1k views

Original Post

Jan 8, 2003 at 1:51 PM

i need to create an array of doubles, of dimensions [3][n] at the moment I am using 3 separate arrays like so: __________________________________ n = 23; double *x; x = (double *) new double[n]; double *y; y = (double *) new double[n]; double *z; z = (double *) new double[n]; __________________________________ what would make it much better would be if I could make an array of structs called, say, testPoints but I dont really know how to do that... can I just declare a struct in my header file like so __________________________________ struct TESTPOINTS{ double x =0; double y =0; double z =0; } __________________________________ then write: __________________________________ TESTPOINTS *points; points = (TESTPOINTS *) new TESTPOINTS[n]; _______________________ and if someone could tell me what a TYPEDEF means i would love you lots! thanks Joe

djsteffey

165

djsteffey

Jan 8, 2003 at 2:04 PM

you dont really need typedef for c++

  
struct TESTPOINTS
{
   double x;
   double y;
   double z;
};
.
.
.
.
TESTPOINTS*   points;
points = new TESTPOINTS[n];

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- Mr. T

CpMan

Jan 8, 2003 at 2:09 PM

quote:
Original post by ncsu121978
you dont really need typedef for c++

Nonsense. Who told you that. It''s incredibly useful for reducing code length in some cases, aliasing names together (how do you think you think the standard library does some things). Furthermore, if you''re doing things like template metapogramming, it''s neccesary in many cases.

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Fruny

203

Fruny

Jan 8, 2003 at 2:14 PM

Yes.


struct TESTPOINTS 
{
  double x,y,z;  // no default initialisers.
}

TESTPOINTS *points;
points = new TESTPOINTS[n]; // no need for a cast, new return ''the right type''.

delete[] point; // use the array version of delete to match new[]

A typedef creates an alias for a type : both names refer to the same type. Syntax is the same as declaring a variable, except with typedef in front.

typedef TESTPOINT Foo; // Foo is now the same type as TESTPOINT.

Hungry Joe

Author

Hungry Joe

Jan 8, 2003 at 3:45 PM

thanks folks! you''ve been a great help!

djsteffey

165

djsteffey

Jan 12, 2003 at 12:06 AM

sorry....i was thinking of #define
they suggest to use const instead of #define for c++

example

  
#define  MAX_POINTS   100

or

const int MAX_POINTS = 100;

they recommend the 2nd way for c++....not sure why...something about the compiler knowing it is a type or something.
Although i use the first method....since it will save on memory a little bit.

"I pity the fool, thug, or soul who tries to take over the world, then goes home crying to his momma."
- Mr. T

mond

Jan 12, 2003 at 12:16 AM

quote:
Although i use the first method....since it will save on memory a little bit.

Unless you''re writing C++ code for a wristwatch, I wouldn''t worry too much about the memory you''re using by switching from #define to const declarations. Pick the route that gives you the most robust code, then optimize from there if you find the need.

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