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.
Related
In older versions of Delphi, like D7, you could do like ord(s[i]) where s was a string, but trying this with an AnsiString results in an exception (access violation).
P.S. I was w/delphi 7 for a long time.
Here are the steps to reproduce the error:
Create a new project and through a memo on the form (let it be memo1) than add the following code to the form create event handler:
procedure TForm1.FormCreate(Sender: TObject);
var u: ansistring;
begin
u := 'stringtest';
memo1.Lines.Add(inttostr(ord(u[2])));
end;
For me this code produces an AV.
It does work with an ansistring, but you cannot read past the end of it and you must make sure the string is initialized.
function CharCode(const S: ansistring; pos: integer): byte;
begin
if pos <= 0 then result:= 0
//else if s='' then Result:= 0 //unassigned string;
else if Length(s) < Pos then Result:= 0 //cannot read past the end.
else Result:= Ord(s[pos]);
end;
Note that if s='' is the same as asking if pointer(s) = nil. An empty string is really a nil pointer.
This is probably why you where getting an access violation.
If you want to force the ansistring to be a certain length you can use SetLength(MyAnsistring, NewLength);
The length of the (ansi)string is variable. That means it grows and shrinks as needed. If you read past the end of the string you may get an access violation.
Note that you don't have to get an AV, the RTL leaves a bit of slack in its allocation; it usually allocates a slightly bigger buffer than requested, this is due to performance and architectural reasons.
The other reason why you may not get an AV if reading past the end of a string is that your program may own both the string buffer and whatever happens to be right next to it.
For this reason it is a good idea to enable range checking in debug mode {$R+} it adds extra checks to protect against reading past the end of structures.
The difference between shortstring and (ansi)string
A short string has a fixed length and it lives on the stack.
A long string (ansi or wide) is a pointer to a record that gets allocated on the heap; it looks like this:
type
TStringRecord = record
CodePage: word;
ElementSize: word; //(1, 2 or 4)
ReferenceCount: integer;
Length: Integer;
StringData: array[1..length(s)] of char;
NullChar: char;
end;
The compiler hides all these details from you.
see: http://docwiki.embarcadero.com/RADStudio/Seattle/en/Internal_Data_Formats
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.
Please excuse the silly question, but I'm confused. Consider the following method (sorry for noisy comments, this is a real code under development):
function HLanguages.GetISO639LangName(Index: Integer): string;
const
MaxIso639LangName = 9; { see msdn.microsoft.com/en-us/library/windows/desktop/dd373848 }
var
LCData: array[0..MaxIso639LangName-1] of Char;
Length: Integer;
begin
{ TODO : GetLocaleStr sucks, write proper implementation }
//Result := GetLocaleStr(LocaleID[Index], LOCALE_SISO639LANGNAME, '??');
Length := GetLocaleInfo(LocaleID[Index], LOCALE_SISO639LANGNAME, #LCData, System.Length(LCData));
Win32Check(Length <> 0);
SetString(Result, #LCData, Length); // "E2008 Incompatible types" here, but why?
end;
If I remove the reference operator then implicit cast from $X+ comes to the rescue and method compiles. Why compiler refuses this code with reference operator is beyond my understanding.
This is Delphi XE2 and this behaviour might be specific to it.
And if I add a test-case dummy with equivalent prototype as intrinsic one within the scope of HLanguages.GetISO639LangName this error will magically go away:
procedure SetString(var s: string; buffer: PChar; len: Integer);
begin
{ test case dummy }
end;
You have to explicitly convert it to PChar:
SetString(result,PChar(#LCData),Length);
As you stated, SetString() is very demanding about the 2nd parameter type. It must be either a PChar either a PWideChar either a PAnsiChar, depending on the string type itself.
I suspect this is due to the fact that SetString() is defined as overloaded with either a string, a WideString, or an AnsiString as 1st parameter. So in order to validate the right signature, it needs to have exact match of all parameters types:
SetString(var s: string; buf: PChar; len: integer); overload;
SetString(var s: AnsiString; buf: PAnsiChar; len: integer); overload;
SetString(var s: WideString; buf: PWideChar; len: integer); overload;
Of course, all those are "intrinsics", so you won't find such definition in system.pas, but directly some procedure like _LStrFromPCharLen() _UStrFromPCharLen() _WStrFromPWCharLen() or such.
This behavior is the same since early versions of Delphi, and is not a regression in XE2.
I think there's a compiler bug in there because the behaviour with SetString differs from the behaviour with overloaded functions that you provide. What's more there's an interaction with the Typed # operator compiler option. I don't know how you set that. I always enable it but I suspect I'm in the minority there.
So I cannot explain the odd behaviour, and answer the precise question you ask. I suspect the only way to answer it is to look at the internals of the compiler, and very few of us can do that.
Anyway, in case it helps, I think the cleanest way to pass the parameter is like so:
SetString(Result, LCData, Length);
This compiles no matter what you set Typed # operator to.
I know this doesn't answer the specific question regarding SetString, but I'd like to point out that you can do the same thing by simply writing
Result := LCData;
When assigning to a string, Delphi treats a static array of char with ZERO starting index, as a Null terminated string with maximum length. Consider the following:
var
IndexOneArray : array [ 1 .. 9 ] of char;
IndexZeroArray : array [ 0 .. 8 ] of char;
S : string;
T : string;
begin
IndexOneArray := 'ABCD'#0'EFGH';
IndexZeroArray := 'ABCD'#0'EFGH';
S := IndexOneArray;
T := IndexZeroArray;
ShowMessage ( 'S has ' + inttostr(length(S)) + ' chars. '
+ #13'T has ' + inttostr(length(T)) + ' chars. ' );
end;
This displays a message that S has 9 chars, while T has 4.
It will also work when the zero-index array has 9 non-null characters. The result will be 9 characters regardless of what's in the following memory locations.
Because LCData is pointer to the array, not to the Char. Sure, sometimes it happens that an array or a record or a class start with char-type variable, but consequences are not what statically-typed compiler should rely upon.
You have to take the pointer to a character in that array, not to the array itself.
SetString(Result, #LCData[Low(LCData)], Length);
I am having a problem acquiring the friendly name (dbcp_name) from DEV_BROADCAST_PORT using delphi.
I have tried using the microsoft help documentation which says it is a pointer to a null terminated string, but on that page there is a comment which indicates it is a variable-length structure, and dbcp_name is an array that contains the actual characters of the port name.
I have tried to extract this but I currently have not found a way as when I get it to return anything it is complete gibberish.
The code I have used follows:
PDevBroadcastPort = ^DEV_BROADCAST_PORT;
DEV_BROADCAST_PORT = packed record
dbcp_size : DWORD ;
dbcp_devicetype : DWORD;
dbcp_reserved : DWORD ;
dbcp_name : array[0..0] of ansichar; //TCHAR dbcp_name[1]; not valid
end;
I have tried different values for the length of the array, I had read somewhere that this was the correct declaration but I am not entirely sure. Also the commented out line is what the microsoft document gives for the line in C++
To extract the information I have tried this:
var
PData: PDevBroadcastPort;
FName: string;
...
PData := PDevBroadcastPort(Msg.lParam);
ShowMessage('Length '+Inttostr(length(PData^.dbcp_name)));
FName := '';
i:=0;
while((PData^.dbcp_name[i]) <> #0) and (i < 100) do
begin
FName := FName + (PData.dbcp_name[i]);
i := i +1;
ShowMessage(FName);
end;
I have tried setting the while loop to terminate at the length of the data structure but if I dont set it then it becomes huge.
Any help is appreciated and if I have left out any code which is needed for this question please let me know and I shall acquire it as soon as I can.
Thanks
The documentation doesn't say it's a pointer to a null-terminated string; it says it is a null-terminated string. That's typical for arrays that are declared at the end of a record with a length of just one element.
There's actually more memory after the designated record size, and that memory holds the remaining characters of the string. A pointer to that record field is also a pointer to the character data.
FName := PAnsiChar(#PData.dbcp_name);
Your array-traversing code should work, too, assuming you have bounds checking disabled for that stretch of code (or else you'd get an exception when the program detected you reading beyond the first element of the array).
That all presupposes that PData really is a pointer to a Dev_Broadcast_Port structure. You've given no information about what message you're handing, so I don't know whether you really have what you think you have.
If you're using Delphi 2009 or later, then the TCHAR type in the C declaration is equivalent to Delphi's WideChar type. Interpreting the field as an array of AnsiChar will get you wrong results, although for most port names, it might appear as though the array is a list of null-terminated one-character strings. Unless you're sure you have non-Unicode data, you should just use Char and PChar, and let the Delphi version determine which data type you have.
FName := PChar(#PData.dbcp_name);
The dbcp_name field contains the actual characters. The length of the character data, minus the null terminator, is dbcp_size - SizeOf(DEV_BROADCAST_PORT), so you can grab the name like this:
type
DEV_BROADCAST_PORTA = packed record
dbcp_size : DWORD;
dbcp_devicetype : DWORD;
dbcp_reserved : DWORD;
dbcp_name : array[0..0] of AnsiChar;
end;
DEV_BROADCAST_PORTW = packed record
dbcp_size : DWORD;
dbcp_devicetype : DWORD;
dbcp_reserved : DWORD;
dbcp_name : array[0..0] of WideChar;
end;
{$IFDEF UNICODE}
DEV_BROADCAST_PORT = DEV_BROADCAST_PORTW;
{$ELSE}
DEV_BROADCAST_PORT = DEV_BROADCAST_PORTA;
{$ENDIF}
PDEV_BROADCAST_PORT = ^DEV_BROADCAST_PORT;
.
var
PData: PDEV_BROADCAST_PORT;
FName: string;
...
PData := PDEV_BROADCAST_PORT(Msg.lParam);
SetString(FName, PData^.dbcp_name, (PData^.dbcp_size - SizeOf(DEV_BROADCAST_PORT)) div SizeOf(Char));
ShowMessage(FName);
I found a Windows API function that performs "natural comparison" of strings. It is defined as follows:
int StrCmpLogicalW(
LPCWSTR psz1,
LPCWSTR psz2
);
To use it in Delphi, I declared it this way:
interface
function StrCmpLogicalW(psz1, psz2: PWideChar): integer; stdcall;
implementation
function StrCmpLogicalW; external 'shlwapi.dll' name 'StrCmpLogicalW';
Because it compares Unicode strings, I'm not sure how to call it when I want to compare ANSI strings. It seems to be enough to cast strings to WideString and then to PWideChar, however, I have no idea whether this approach is correct:
function AnsiNaturalCompareText(const S1, S2: string): integer;
begin
Result := StrCmpLogicalW(PWideChar(WideString(S1)), PWideChar(WideString(S2)));
end;
I know very little about character encoding so this is the reason of my question. Is this function OK or should I first convert both the compared strings somehow?
Keep in mind that casting a string to a WideString will convert it using default system codepage which may or may not be what you need. Typically, you'd want to use current user's locale.
From WCharFromChar in System.pas:
Result := MultiByteToWideChar(DefaultSystemCodePage, 0, CharSource, SrcBytes,
WCharDest, DestChars);
You can change DefaultSystemCodePage by calling SetMultiByteConversionCodePage.
The easier way to accomplish the task would be to declare your function as:
interface
function StrCmpLogicalW(const sz1, sz2: WideString): Integer; stdcall;
implementation
function StrCmpLogicalW; external 'shlwapi.dll' name 'StrCmpLogicalW';
Because a WideString variable is a pointer to a WideChar (in the same way an AnsiString variable is a pointer to an AnsiChar.)
And this way Delphi will automatically "up-convert" an AnsiString to a WideString for you.
Update
And since we're now in the world of UnicodeString, you would make it:
interface
function StrCmpLogicalW(const sz1, sz2: UnicodeString): Integer; stdcall;
implementation
function StrCmpLogicalW; external 'shlwapi.dll' name 'StrCmpLogicalW';
Because a UnicodeString variable is still a pointer to a \0\0 terminated string of WideChars. So if you call:
var
s1, s1: AnsiString;
begin
s1 := 'Hello';
s2 := 'world';
nCompare := StrCmpLogicalW(s1, s2);
end;
When you try to pass an AnsiString into a function that takes a UnicodeString, the compiler will automatically call MultiByteToWideChar for you in the generated code.
CompareString supports numeric sorting in Windows 7
Starting in Windows 7, Microsoft added SORT_DIGITSASNUMBERS to CompareString:
Windows 7: Treat digits as numbers during sorting, for example, sort "2" before "10".
None of this helps answer the actual question, which deals with when you have to convert or cast strings.
There might be an ANSI variant for your function to (I haven't checked). Most Wide API's are available as an ANSI version too, just change the W suffix to an A, and you're set. Windows does the back-and-forth conversion transparantly for you in that case.
PS: Here's an article describing the lack of StrCmpLogicalA : http://blogs.msdn.com/joshpoley/archive/2008/04/28/strcmplogicala.aspx
Use System.StringToOleStr, which is a handy wrapper around MultiByteToWideChar, see Gabr's answer:
function AnsiNaturalCompareText(const S1, S2: string): integer;
var
W1: PWideChar;
W2: PWideChar;
begin
W1 := StringToOleStr(S1);
W2 := StringToOleStr(S2);
Result := StrCmpLogicalW(W1, W2);
SysFreeString(W1);
SysFreeString(W2);
end;
But then, Ian Boyd's solution looks and is much nicer!