I want to use a function from FMOD library that locks data in memory of a given sound and returns pointer to the data, so some reading or modification of the data can be done:
function FSOUND_Sample_Lock(Sptr: PFSoundSample; Offset: Integer; Length: Integer;
var Ptr1: Pointer; var Ptr2: Pointer; var Len1: Cardinal;
var Len2: Cardinal): ByteBool;
ptr1 and ptr2 is a pointer to memory, len1 and len2 is length of the data in the memory.
How can I iterate over the data at ptr1 reading each time next SmallInt ?
I'm using Delphi 7 so {$POINTERMATH ON} does not work
In a modern Delphi, with {$POINTERMATH ON}, you can index the elements of the array like this:
PSmallint(ptr1)[i]
If you don't have $POINTERMATH in your Delphi, or if you prefer to leave it off, you can do this:
type
TSmallintArray = array[0..MaxInt div SizeOf(Smallint)-1] of Smallint;
PSmallintArray = ^TSmallintArray;
And then access the elements with:
PSmallintArray(ptr1)[i]
Personally I've never found the latter approach to my tastes, but the choice is yours.
Related
Given a buffer and its size in bytes, is there a way to convert this to TBytes without copying it?
Example:
procedure HandleBuffer(_Buffer: PByte; _BufSize: integer);
var
Arr: TBytes;
i: Integer;
begin
// some clever code here to get contents of the buffer into the Array
for i := 0 to Length(Arr)-1 do begin
HandleByte(Arr[i]);
end;
end;
I could of course copy the data:
procedure HandleBuffer(_Buffer: PByte; _BufSize: integer);
var
Arr: TBytes;
i: Integer;
begin
// this works but is very inefficient
SetLength(Arr, _BufSize);
Move(PByte(_Buffer)^, Arr[0], _BufSize);
//
for i := 0 to Length(Arr)-1 do begin
HandleByte(Arr[i]);
end;
end;
But for a large buffer (about a hundred megabytes) this would mean I have double the memory requirement and also spend a lot of time unnecessarily copying data.
I am aware that I could simply use a PByte to process each byte in the buffer, I'm only interested in a solution to use a TBytes instead.
I think it's not possible, but I have been wrong before.
No, this is not possible (without unreasonable hacks).
The problem is that TBytes = TArray<Byte> = array of Byte is a dynamic array and the heap object for a non-empty dynamic array has a header containing the array's reference count and length.
A function that accepts a TBytes parameter, when given a plain pointer to an array of bytes, might (rightfully) attempt to read the (non-existing) header, and then you are in serious trouble.
Also, dynamic arrays are managed types (as indicated by the reference count I mentioned), so you might have problems with that as well.
However, in your particular example code, you don't actually use the dynamic array nature of the data at all, so you can work directly with the buffer:
procedure HandleBuffer(_Buffer: PByte; _BufSize: integer);
var
i: Integer;
begin
for i := 0 to _BufSize - 1 do
HandleByte(_Buffer[i]);
end;
I'm using Delphi XE and the Matlab 2012B compiler on Windows 7.
I'm trying to write several wrapper functions so DLL files created with the Matlab 2012b Compiler can be more easily called from Delphi XE. I found that I should use the _proxy functions when using the MCR, which indeed allowed me to call several functions successfully. I can also pass strings to Matlab without problems by passing them as PAnsiChar.
I'm currently trying to create a StructArray with some field names.
As I've already successfully created numeric arrays and matrices, I'm pretty sure the first 2 parameters are OK. I expect the last one is causing the error, but I don't know how to solve this (yet). Looking at the Matlab help and example files I'm doing what should be done. Obviously I'm wrong...
I know that with Matlab r13 we had to pass the fieldnames as an array[0..n] of pAnsiChar instead of an array of pAnsiChar. I tried this here as well to no avail.
Can someone tell me if I have indeed made the correct function mapping to mxCreateStructArray(_730_proxy) and if I'm passing the parameters as expected?
type
mxArray = pointer;
// mxArray *mxCreateStructArray(mwSize ndim, const mwSize *dims, int nfields, const char **fieldnames);
function MCRdll_CreateStructArray(aDimCount: integer; aDims: pointer; aFieldCount: integer; aFields: PPAnsiChar): mxArray; cdecl; external 'mclmcrrt8_0.dll' name 'mxCreateStructArray_730_proxy';
function MCR_CreateStructArray(aFieldNames: TArray<string>): mxArray;
var
i: integer;
lstDims: array of integer;
lstNames: array of pAnsiChar;
begin
SetLength(lstNames, Length(aFieldNames));
for i := 0 to Length(aFieldNames) - 1 do
lstNames[i] := ToPAnsiChar(aFieldNames[i]); //Creates a new PAnsiChar with the content of aFieldNames[i]
SetLength(lstDims, 2);
lstDims[0] := 1;
lstDims[1] := Length(aFieldNames);
//This call raises an "External Exception" from Matlab.
Result := MCRdll_CreateStructArray(Length(lstDims), #lstDims, Length(lstNames), #lstNames);
end;
The MATLAB C API function is:
mxArray *mxCreateStructArray(mwSize ndim, const mwSize *dims,
int nfields, const char **fieldnames);
As I understand it, mwSize is by default the same as int. That translates to Integer in Delphi. The const char** parameter is the address of an array of const C strings. Translate that to Delphi and you have:
function MCRdll_CreateStructArray(ndim: Integer; dims: PInteger;
nFields: Integer; fieldnames: PPAnsiChar): mxArray; cdecl;
external 'mclmcrrt8_0.dll' name 'mxCreateStructArray_730_proxy';
Now, how to get the parameters. Well, assuming you want a vector, dims is an array of length 2, and ndim is that length. I'd declare that as a static array:
var
dims: array [0..1] of Integer;
As for the field names, those are variable length. So you need a dynamic array of PAnsiChar. That is:
var
fieldnames: array of PAnsiChar;
You also need to pass the vector length for your struct array to your function. That makes your function be something like this:
function MCR_CreateStructArray(len: Integer;
const aFieldNames: array of AnsiString): mxArray;
var
i: integer;
dims: array [0..1] of Integer;
fieldnames: array of PAnsiChar;
begin
if Length(aFieldNames)=0 then
begin
Result := nil;
exit;
end;
dims[0] := 1;
dims[1] := len;
SetLength(fieldnames, Length(aFieldNames));
for i := 0 to high(fieldnames) do
fieldnames[i] := PAnsiChar(aFieldNames[i]);
Result := MCRdll_CreateStructArray(Length(dims), #lstDims[0],
Length(fieldnames), #fieldnames[0]);
end;
An alternative to the final parameter is to pass PPAnsiChar(fieldnames). That works because a dynamic array variable is the address of the first element.
So, what was wrong with your version? The biggest mistake you made was to use untyped pointers for the two arrays that you pass to MCRdll_CreateStructArray. This means that the compiler cannot check that you got the indirection correct. And you did not.
First of all in your code you pass #lstDims to the second parameter. Now lstDims is a dynamic array in your code. The implementation of that has lstDims being a pointer to the first element. So, informally, lstDims has type ^Integer. And therefore #lstDims has type ^^Integer. That's one level of indirection too far. And you made the exact same mistake in the final parameter.
One final point. I've change the signature of the function to receive an array of AnsiString. That's the easy way for me to write the code because I don't need to worry about the UTF-16 to ANSI conversion, and can use a simple PAnsiChar cast. You'd probably benefit from this helper:
function ToAnsiStringArray(const arr: array of string): TArray<AnsiString>;
var
i: Integer;
begin
SetLength(Result, Length(arr));
for i := 0 to high(Result) do
Result[i] := AnsiString(arr[i]);
end;
I've not compiled any of this so there may be some imprecision. I trust you'll not be put off by that.
As the topic indicates above, I'm wondering if there's a good example of a clean and efficient way to handle pointers as passed in function parms when processing the data sequentially. What I have is something like:
function myfunc(inptr: pointer; inptrsize: longint): boolean;
var
inproc: pointer;
i: integer;
begin
inproc := inptr;
for i := 1 to inptrsize do
begin
// do stuff against byte data here.
inc(longint(inproc), 1);
end;
end;
The idea is that instead of finite pieces of data, I want it to be able to process whatever is pushed its way, no matter the size.
Now when it comes to processing the data, I've figured out a couple of ways to do it successfully.
Assign the parm pointers to identical temporary pointers, then use those to access each piece of data, incrementing them to move on. This method is quickest, but not very clean looking with all the pointer increments spread all over the code. (this is what I'm talking about above)
Assign the parm pointers to a pointer representing a big array value and then incremently process that using standard table logic. Much cleaner, but about 500 ms slower than #1.
Is there another way to efficiently handle processing pointers in this way, or is there some method I'm missing that will both be clean and not time inefficient?
Your code here is basically fine. I would always choose to increment a pointer than cast to a fake array.
But you should not cast to an integer. That is semantically wrong and you'll pay the penalty anytime you compile on a platform that has pointer size different from your integer size. Always use a pointer to an element of the right size. In this case a pointer to byte.
function MyFunc(Data: PByte; Length: Integer): Boolean;
var
i: Integer;
begin
for i := 1 to Length do
begin
// do stuff against byte data here.
inc(Data);
end;
end;
Unless the compiler is having a really bad day, you won't find it easy to get better performing code than this. What's more, I think this style is actually rather clear and easy to understand. Most of the clarity gain comes in avoiding the need to cast. Always strive to remove casts from your code.
If you want to allow any pointer type to be passed then you can write it like this:
function MyFunc(P: Pointer; Length: Integer): Boolean;
var
i: Integer;
Data: PByte;
begin
Data := P;
for i := 1 to Length do
begin
// do stuff against byte data here.
inc(Data);
end;
end;
Or if you want to avoid pointers in the interface, then use an untyped const parameter.
function MyFunc(const Buffer; Length: Integer): Boolean;
var
i: Integer;
Data: PByte;
begin
Data := PByte(#Buffer);
for i := 1 to Length do
begin
// do stuff against byte data here.
inc(Data);
end;
end;
Use a var parameter if you need to modify the buffer.
I have a different opinion: For sake of readability I would use an array. Pascal was not designed to be able to access memory directly. Original pascal did not even have pointer arithmetic.
This is how I would use an array:
function MyFunc(P: Pointer; Length: Integer): Boolean;
var
ArrayPtr : PByteArray Absolute P;
I : Integer;
begin
For I := 0 to Length-1 do
// do stuff against ArrayPtr^[I]
end;
But if performance matters, I would write it like this
function MyFunc(P: Pointer; Length: Integer): Boolean;
var
EndOfMemoryBlock: PByte;
begin
EndOfMemoryBlock := PByte(Int_Ptr(Data)+Length);
While P<EndOfMemoryBlock Do begin
// do stuff against byte data here.
inc(P);
end;
end;
I am using: HawkNL library.
There is an nlRead procedure as follows:
function nlRead(socket: NLsocket; var buffer; nbytes: NLint): NLint;
In all examples and other resources a static array is used to read the bytes to.
Just something like this:
FBufArray = array [0..1024] of Byte;
I have a few questions regarding this matter.
Which model/type would be appropriate to satisfy nlRead function that I could
dynamically allocate space for read data?
I was trying to use Pointer and GetMem or dynamic table with SetLength, but It seemed not to work as it should.
What is the correct approach in the situation when I have to read bytes with the unknown speed and do it as fast as possible. I mean What should be the size of the buffor for example?
For me it is relevant because read bytes I have to re-send further at the same time.
Generally how can I read and send bytes as fast as it is possible?
If your question is about what to pass as 'buffer'. You can pass anything you like.
If you pass a pointer you have to dereference it. For example when you call nl Read
Procedure read;
Type
TChunk = record
data: pointer;
datasize: NLint;
End;
Var
Chunk: TChunk;
Const
IdealReadSize = 1024;
Begin
GetMem( Chunk.data, IdealReadSize);
Try
Chunk.datasize := nlRead( YourSocket, Chunk.data^, IdealReadSize );
// Chunk.datasize hold the count of bytes which have been effectively read
// (maybe less than 1024 in case of an error)
// do something with your chunk
Finally
Freemem( Chunk.data, IdealReadSize );
End;
End;
It's the same approach as the TStream.Read() procedure.
You could use an untyped pointer: var P: Pointer;, allocate with GetMem or AllocMem, pass it to your function dereferenced: nlRead(Socket, P^, Count); and deallocate with FreeMem.
With regard to speed, a static buffer, sufficiently large: Buf: array[0..BufSize - 1] of Byte is probably the best.
Question One
I have
var example : array[0..15] of char;
I want to assign the value from an input to that variable
example := inputbox('Enter Name', 'Name', '');
In the highscores unit I have record and array
type
points = record
var
_MemoryName : array[0..15] of char;
_MemoryScore : integer;
end;
var
rank : array[1..3] of points;
var s: string;
a: packed array[0..15] of char;
highscoresdata.position[1]._MemoryName := StrPLCopy(a, s, Length(a)) ;
returns -> (186): E2010 Incompatible types: 'array[0..15] of Char' and 'PWideChar'
var s: string;
a: packed array[0..15] of char;
s := InputBox('caption', 'Caption', 'Caption');
FillChar(a[0], length(a) * sizeof(char), #0);
Move(s[1], a[0], length(a) * sizeof(char));
scores.rank[1]._MemoryName := <<tried both s and a>> ;
returns (189): E2008 Incompatible types
Question One
There are many ways. One is:
procedure TForm1.FormCreate(Sender: TObject);
var
s: string;
a: packed array[0..15] of char;
begin
s := InputBox(Caption, Caption, Caption);
assert(length(s) <= 16);
FillChar(a[0], length(a) * sizeof(char), #0);
Move(s[1], a[0], length(s) * sizeof(char));
end;
But there might be a more elegant solution to your original problem, I suspect.
Question Two
Every time you wish a function/procedure didn't have a particular argument, you should realize that there might be a problem with the design of the project. Nevertheless, it isn't uncommon that Sender parameters are superfluous, because they are almost omnipresent because of the design of the VCL (in particular, the TNotifyEvent). If you know that the receiving procedure doesn't care about the Sender parameter, simply give it anything, like Self or nil.
Question Three
Consider this code:
procedure TForm4.FormCreate(Sender: TObject);
var
a: packed array[0..15] of char;
b: packed array[0..15] of char;
begin
a := b;
end;
This doesn't work. You cannot treat arrays like strings; in particular, you cannot assign static arrays like this (a := b).
Instead, you have to do something like...
Move(b[0], a[0], length(a) * sizeof(char));
...or simply loop and copy one value at a time. But the above simple assignment (a := b) does work if you declare a static array type:
type
TChrArr = packed array[0..15] of char;
procedure TForm4.FormCreate(Sender: TObject);
var
a: TChrArr;
b: TChrArr;
begin
b := a;
end;
Andreas has you covered for question 1.
Question 2
I would arrange that your event handler called another method:
procedure TForm5.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
RespondToEditControlKeyPress;
end;
That way you can just call RespondToEditControlKeyPress directly.
I'd guess that you want to call it with no parameters because you want code to run when the edit control's text is modified. You could perhaps use the OnChange event instead. And it may be that OnChange is more appropriate because pressing a key is not the only way to get text into an edit control.
By the way, it's better to ask one question at a time here on Stack Overflow.
For a quick way to copy string-type values into array-of-character type values. I suggest a small helper function like this:
procedure StrToCharArray( inputStr:String; var output; maxlen:Integer);
type
ArrayChar = Array[0..1] of Char;
begin
StrLCopy( PChar(#ArrayChar(output)[0]),PChar(inputStr),maxlen);
end;
Each time you call it, pass in the maximum length to be copied. Remember that if the buffer length is 15, you should pass in 14 as the maxlen, so that you leave room for the terminating nul character, if you intend to always terminate your strings:
StrToCharArray( UserInputStr, MyRecord.MyField, 14 );
This function will ensure that the data you copy into the record is null terminated, assuming that's what you wanted. Remember that in a fixed length character array it's up to you to decide what the rules are. Null terminated? Fully padded with spaces or null characters.... Strings and arrays-of-characters are so different, that there exist multiple possible ways of converting between the two.
If you don't intend to terminate your strings with nul, then you should use the FillChar+Move combination shown in someone else's answer.
The obvious answer is of course.
Don't use a packed array of char.
Use a string instead.
If you use ansistring, 1 char will always take 1 byte.
If you use shortstring ditto.
Ansistring is compatible with Pchar which is a pointer to a packed array of char.
So you can write
function inputbox(a,b,c: ansistring): pchar;
begin
Result:= a+b+c;
end;
var s: ansistring;
begin
s:= inputbox('a','b','c');
end;
Some advice
It looks like your are translating code from c to Delphi.
a packed array of char is exactly the same as the old (1995) shortstring minus the length byte at the beginning of shortstring.
The only reason I can think of to use packed array of char is when you are reading data to and from disk, and you have legacy code that you don't want to change.
I would keep the legacy code to read and write from disk and then transfer the data into an ansistring and from there on only use ansistring.
It's soooooooo much easier, Delphi does everything for you.
And... ansistring is much faster, gets automatically created and destroyed, can have any length (up to 2GB), uses less memory --because identical strings only get stored once (which means stringa:= stringb where a string is 20 chars is at least 5x faster using ansistrings than array's of char).
And of course best of all, buffer overflow errors are impossible with ansistring.
What about unicodestring?
Unicodestring is fine to use, but sometimes translation of chars happens when converting between packed array of char and unicodestring, therefore I recommend using ansistring in this context.
What you try to do is impossible, indeed:
highscoresdata.position[1]._MemoryName := StrPLCopy(a, s, Length(a));
That tries to assign a pointer (the result of StrPLCopy, a PWideChar in the last few versions of Delphi) to an array, which is indeed impossible. You can't copy an array like that. I would do:
StrLCopy(highscoresdata.position[1]._MemoryName, PChar(s),
Length(highscoresdata.position[1]._MemoryName));
That should work, and is IMO the simplest solution to copy a string to an array of characters. There is no need to use a as some kind of intermediate, and using Move is, IMO, rather low level and therefore a little tricky (it is easy to forget to multiply by the size of a character, it is unchecked, it does not add a #0, etc.), especially if you don't know what exactly you are doing.
This solution should even work for versions of Delphi before Delphi 2009, as it does not rely on the size of the character.
FWIW, I would not use packed arrays. Packed doesn't have a meaning in current Delphi, but could confuse the compiler and make the types incompatible.