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digitalmars.D.learn - filling arrays, avoid default init

reply "Frank Benoit (keinfarbton)" <benoit tionex.removethispart.de> writes:
TypeA[] ta = .... ; // big array with something
TypeB[] tb;
tb.length = ta.length; // (1)
foreach( uint i, TypeA a; ta ){
  tb[i] = ta[i].getB();
}

(1) how can I avoid the default initialization?

-- Frank
Jan 09 2007
parent reply Lionello Lunesu <lio lunesu.remove.com> writes:
Frank Benoit (keinfarbton) wrote:

 TypeA[] ta = .... ; // big array with something
 TypeB[] tb;
 tb.length = ta.length; // (1)
 foreach( uint i, TypeA a; ta ){
   tb[i] = ta[i].getB();
 }
 
 (1) how can I avoid the default initialization?
 
 -- Frank



type[] t = void;
Jan 09 2007
parent reply Lionello Lunesu <lio lunesu.remove.com> writes:
Lionello Lunesu wrote:

 Frank Benoit (keinfarbton) wrote:

 TypeA[] ta = .... ; // big array with something
 TypeB[] tb;
 tb.length = ta.length; // (1)
 foreach( uint i, TypeA a; ta ){
   tb[i] = ta[i].getB();
 }

 (1) how can I avoid the default initialization?

 -- Frank



 type[] t = void;



Uhm, sorry. That doesn't seem to prevent the initialization at all...

L.
Jan 09 2007
parent reply Thomas Kuehne <thomas-dloop kuehne.cn> writes:
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Hash: SHA1

Lionello Lunesu schrieb am 2007-01-09:

 Lionello Lunesu wrote:

 Frank Benoit (keinfarbton) wrote:

 TypeA[] ta = .... ; // big array with something
 TypeB[] tb;
 tb.length = ta.length; // (1)
 foreach( uint i, TypeA a; ta ){
   tb[i] = ta[i].getB();
 }

 (1) how can I avoid the default initialization?

 -- Frank



 type[] t = void;



 Uhm, sorry. That doesn't seem to prevent the initialization at all...



Can you provide a code sampel?

Tested on Linux:
# import std.stdio;
# 
# typedef int X = 12_34_56_78;
# 
# void main(){
#    X[4] a;
#    X[4] b = void;
# 
#    writefln("a: %s", a);
#    writefln("b: %s", b);
# }

a: [12345678,12345678,12345678,12345678]
b: [-607311696,-609996928,0,-608522976]

Thomas


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Jan 09 2007
next sibling parent reply "Lionello Lunesu" <lionello lunesu.remove.com> writes:
 Uhm, sorry. That doesn't seem to prevent the initialization at all...



 Can you provide a code sampel?



Well, Frank's code:

TypeA[] ta = .... ; // big array with something
TypeB[] tb = void;
tb.length = ta.length; // (1)
foreach( uint i, TypeA a; ta ){
  tb[i] = ta[i].getB();
}

For unsized dynamic arrays (TypeB[]), =void does not prevent the 
initialization when you change the length later.

L.
Jan 09 2007
parent reply Thomas Kuehne <thomas-dloop kuehne.cn> writes:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Lionello Lunesu schrieb am 2007-01-10:

 Uhm, sorry. That doesn't seem to prevent the initialization at all...



 Can you provide a code sampel?



 Well, Frank's code:

 TypeA[] ta = .... ; // big array with something
 TypeB[] tb = void;
 tb.length = ta.length; // (1)
 foreach( uint i, TypeA a; ta ){
   tb[i] = ta[i].getB();
 }

 For unsized dynamic arrays (TypeB[]), =void does not prevent the 
 initialization when you change the length later.



It is working as advertised in
http://www.digitalmars.com/d/declaration.html (Void Initializations)
http://www.digitalamrs.com/d/arrays.html (Setting Dynamic Array Length)

The below code might help solve your problem with new'ing dynamic
arrays. (Windows most likely requires some "import" changes.)

# import internal.gc.gclinux;
# import internal.gc.gcbits;
# import internal.gc.gcx;
# import std.gc;
# 
# /**
#  * Void Initialization of a dynamic GC collected array
#  *
#  * Only use this template if you know what you are doing.
#  */
# template newVoidArray(T){
#    T[] newVoidArray(size_t elements){
#       return (cast(T*) (cast(GC)getGCHandle()).malloc(elements * T.sizeof))[0
.. elements];
#    }
# }
# 
# import std.stdio;
# typedef int X = 12_34_56_78;
# 
# void main(){
#    X[] a = new X[4];
#    X[] b = newVoidArray!(X)(4);
# 
#    writefln("a: %s", a);
#    writefln("b: %s", b);
# }

Thomas


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Jan 10 2007
parent "Frank Benoit (keinfarbton)" <benoit tionex.removethispart.de> writes:
Thanks for the answers.
Frank
Jan 10 2007
prev sibling parent Stewart Gordon <smjg_1998 yahoo.com> writes:
Thomas Kuehne wrote:

 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
 Lionello Lunesu schrieb am 2007-01-09:

 Lionello Lunesu wrote:

 Frank Benoit (keinfarbton) wrote:

 TypeA[] ta = .... ; // big array with something
 TypeB[] tb;
 tb.length = ta.length; // (1)
 foreach( uint i, TypeA a; ta ){
   tb[i] = ta[i].getB();
 }

 (1) how can I avoid the default initialization?

 -- Frank












Actually, it's unpredictable, even dangerous.


 Can you provide a code sampel?



----------
import std.stdio;

void main() {
     int[] data = void;

     writefln("%08x %08x", data.ptr, data.length);
     data.length = 16;
     writefln("%08x %08x", data.ptr, data.length);
     writefln(data);
}
----------

You'll be lucky if the last statement doesn't throw an AV.  The danger 
arises if you try to write to the memory at the uninitialised pointer.


 Tested on Linux:
 # import std.stdio;
 # 
 # typedef int X = 12_34_56_78;
 # 
 # void main(){
 #    X[4] a;
 #    X[4] b = void;




Of course that works.  That's a static array.

Stewart.
Jan 11 2007