I want to read byte by byte with a TStream (streamIn) or any stream from cache file.
I don' t know Streams well, actually i want to read cache file but byte by byte.
When this "read" function called from another class it must be read next byte in cache file. But TStream has no "readbyte" method.
function TStringInputStream.read : Integer;
begin
if not back then
lastByte:= streamIn.ReadByte -> ???
back:= false;
Result:= lastByte;
end;
function TStringInputStream.readLine: String;
var
c : Integer;
ns : Boolean;
endd : Boolean;
res : String;
begin
ns:= True;
endd:= False;
while not endd do
begin
c:= read;
if (c = -1) and (ns) then
begin
Result:= '';
Exit;
end;
ns:= false;
if (c = LF) or (c = -1) then
endd:= true
else if c = CR then
begin
if read <> LF then
rewind;
endd:= true;
end
else
res:= IntToStr(c);
end;
Result:= res;
end;
Use ReadBuffer to read a single byte.
var
B: Byte;
....
Stream.ReadBuffer(B, SizeOf(B));
Or if you use XE3 or later you can use ReadData.
Stream.ReadData(B);
Related
Is there a method in Delphi to check if a string is a number without raising an exception?
its for int parsing.
and an exception will raise if one use the
try
StrToInt(s);
except
//exception handling
end;
function TryStrToInt(const S: string; out Value: Integer): Boolean;
TryStrToInt converts the string S, which represents an integer-type number in either decimal or hexadecimal notation, into a number, which is assigned to Value. If S does not represent a valid number, TryStrToInt returns false; otherwise TryStrToInt returns true.
To accept decimal but not hexadecimal values in the input string, you may use code like this:
function TryDecimalStrToInt( const S: string; out Value: Integer): Boolean;
begin
result := ( pos( '$', S ) = 0 ) and TryStrToInt( S, Value );
end;
var
s: String;
iValue, iCode: Integer;
...
val(s, iValue, iCode);
if iCode = 0 then
ShowMessage('s has a number')
else
ShowMessage('s has not a number');
Try this function StrToIntDef()
From help
Converts a string that represents an integer (decimal or hex notation) to a number with error default.
Pascal
function StrToIntDef(const S: string; Default: Integer): Integer;
Edit
Just now checked the source of TryStrToInt() function in Delphi 2007. If Delphi 7 dont have this function you can write like this. Its just a polished code to da-soft answer
function TryStrToInt(const S: string; out Value: Integer): Boolean;
var
E: Integer;
begin
Val(S, Value, E);
Result := E = 0;
end;
XE4 and newer:
for ch in s do
TCharacter.IsNumber(ch);
Don't forget:
uses System.Character
In delphi 7 you can use the Val procedure. From the help:
Unit: System
Delphi syntax: procedure Val(S; var V; var Code: Integer);
S is a string-type expression; it must be a sequence of characters that form a signed real number.
V is an integer-type or real-type variable. If V is an integer-type variable, S must form a whole number.
Code is a variable of type Integer.
If the string is invalid, the index of the offending character is stored in Code; otherwise, Code is set to zero. For a null-terminated string, the error position returned in Code is one larger than the actual zero-based index of the character in error.
use this function
function IsNumber(N : String) : Boolean;
var
I : Integer;
begin
Result := True;
if Trim(N) = '' then
Exit(False);
if (Length(Trim(N)) > 1) and (Trim(N)[1] = '0') then
Exit(False);
for I := 1 to Length(N) do
begin
if not (N[I] in ['0'..'9']) then
begin
Result := False;
Break;
end;
end;
end;
For older Delphi versions from delphi 5 help example:
uses Dialogs;
var
I, Code: Integer;
begin
{ Get text from TEdit control }
Val(Edit1.Text, I, Code);
{ Error during conversion to integer? }
if Code <> 0 then
MessageDlg('Error at position: ' + IntToStr(Code), mtWarning, [mbOk], 0);
else
Canvas.TextOut(10, 10, 'Value = ' + IntToStr(I));
end;
In some languages decimal separators are different (for example, '.' is used in English and ',' is used in Russian). For these cases to convert string to real number the following procedure is proposed:
function TryStrToFloatMultiLang(const S : String; out Value : Extended) : Boolean;
var
dc : char;
begin
Result := false;
dc := DecimalSeparator;
DecimalSeparator := '.';
try
Result := TryStrToFloat(S, Value);
except
DecimalSeparator := ',';
Result := TryStrToFloat(S, Value);
end;
DecimalSeparator := dc;
end;
Update
As #Pep mentioned TryStrToFloat catch exceptions, but it returns boolean value. So the correct code is:
function TryStrToFloatMultiLang(const S : String; out Value : Extended) : Boolean;
var
dc : char;
begin
Result := false;
dc := DecimalSeparator;
DecimalSeparator := '.';
Result := TryStrToFloat(S, Value);
if not Result then begin
DecimalSeparator := ',';
Result := TryStrToFloat(S, Value);
end;
DecimalSeparator := dc;
end;
When you using procedure
val(s, i, iCode);
and set value xd ....
val('xd', i, iCode)
as a result we obtain: 13
standard unit Variants
function VarIsNumeric(v:Variant):Boolean
edited :
My file has several lines. I encrypt the file onto a new file. I want to store each line of decrypted file (=a stream) into StringList.
First, I have a file contain :
aa
bb
cc
I encrypt the file with this function :
procedure EnDecryptFile(pathin, pathout: string; Chave: Word) ;
var
InMS, OutMS: TMemoryStream;
cnt: Integer;
C: byte;
begin
InMS := TMemoryStream.Create;
OutMS := TMemoryStream.Create;
try
InMS.LoadFromFile(pathin) ;
InMS.Position := 0;
for cnt := 0 to InMS.Size - 1 do
begin
InMS.Read(C, 1) ;
C := (C xor not (ord(chave shr cnt))) ;
OutMS.Write(C, 1) ;
end;
OutMS.SaveToFile(pathout) ;
finally
InMS.Free;
OutMS.Free;
end;
end;
My purpose now is to store original value of each line into StringList. I don't want to store decrypted file into harddisk, so I use stream.
This is the function to decrypt the file into stream :
procedure DecryptFile(pathin: string; buff: TMemoryStream; Chave: Word);
var
InMS: TMemoryStream;
cnt: Integer;
C: byte;
begin
InMS := TMemoryStream.Create;
try
InMS.LoadFromFile(pathin);
InMS.Position := 0;
for cnt := 0 to InMS.Size - 1 do
begin
InMS.Read(C, 1);
C := (C xor not(ord(Chave shr cnt)));
buff.Write(C, 1);
end;
// buff.SaveToFile('c:\temp\dump.txt') ;
finally
InMS.free;
end;
end;
--
bbuffer := TMemoryStream.Create;
try
DecryptFile(path, bbuffer, 10); //
//ShowMessage(IntToStr(bbuffer.size)); // output : 1000
bbuffer.Position := 0;
SL := TStringList.Create;
try
SL.LoadFromStream(bbuffer);
for I := 0 to SL.Count - 1 do // SL.Count = 1
begin;
//add each line of orginal file into SL??
end;
finally
SL.free;
end;
finally
bbuffer.free;
end;
Load from stream takes a TStream so you can give it a TFileStream as well as an TMemoryStream. The code you posted should work without any problems. What exactly does not work?
You might have to use
bbuffer.Position := 0;
to reset the position to the start of the stream before loading it into the string list.
EDIT: You write single bytes to a stream and then try to load a string list from it. That won't work. The stream is just a collection of bytes. How should the string list know where one string ends and the next one starts? TStringList.SaveToStream writes separator bytes to the stream so that it can parse the string list back. So, you could do your encryption on the string list and then write the whole string list to the stream, then read the stringlist and do the decryption on the string list.
i use to send a data on two separate process but it fails. it works only under same process... this is concept.
//-----------------------------------------------------------------------------------
MainApps
//-----------------------------------------------------------------------------------
Type
PMyrec = ^TMyrec;
TMyrec = Record
name : string;
add : string;
age : integer;
end;
:OnButtonSend
var aData : PMyrec;
begin
new(aData);
aData.Name := 'MyName';
aData.Add := 'My Address';
aData.Age : 18;
SendMessage(FindWindow('SubApps'),WM_MyMessage,0,Integer(#aData));
end;
//-----------------------------------------------------------------------------------
SubApps
//-----------------------------------------------------------------------------------
Type
PMyrec = ^TMyrec;
TMyrec = Record
name : string;
add : string;
age : integer;
end;
:OnCaptureMessage
var
aData : PMyrec;
begin
aData := PMyrec(Msg.LParam);
showmessage(aData^.Name);
end;
You're right. Addresses only have meaning within a single process. The PMyRec value you create in the first process is just a garbage address in the target process.
To send an arbitrary block of memory to another process via a window message, you should use the wm_CopyData message. You give that message the address of the data and the size, and the OS takes care of copying it into the target process's address space.
Since your data includes a string, which is represented internally as a another pointer, it won't be enough to just copy the 12 bytes of your record. You'll need to allocate additional memory to hold the record and the string data in a single block of memory so wm_CopyData can copy it and the target process can read it.
Here's one way to do it, using a stream to collect the data into a single block of memory.
procedure SendRecord(Source, Target: HWnd; const Rec: TMyRec);
var
Buffer: TMemoryStream;
Len: Integer;
CopyData: TCopyDataStruct;
begin
Buffer := TMemoryStream.Create;
try
Len := Length(Rec.name);
Buffer.Write(Len, SizeOf(Len));
if Len > 0 then
Buffer.Write(Rec.name[1], Len * SizeOf(Char));
Len := Length(Rec.add);
Buffer.Write(Len, SizeOf(Len));
if Len > 0 then
Buffer.Write(Rec.add[1], Len * SizeOf(Char));
Buffer.Write(Rec.age, SizeOf(Rec.age));
CopyData.dwData := 0;
CopyData.cbData := Buffer.Size;
CopyData.lpData := Buffer.Memory;
SendMessage(Target, wm_CopyData, Source, LParam(#CopyData));
finally
Buffer.free;
end;
end;
We write the lengths of the strings in addition to the strings' characters so that the recipient knows how many characters belong to each one. The recipient's code will look like this:
procedure TBasicForm.WMCopyData(var Message: TWMCopyData);
var
Rec: TMyRec;
Len: Integer;
Buffer: TStream;
begin
Buffer := TReadOnlyMemoryStream.Create(
Message.CopyDataStruct.lpData, Message.CopyDataStruct.cbData);
try
if Message.CopyDataStruct.dwData = 0 then begin
Buffer.Read(Len, SizeOf(Len));
SetLength(Rec.name, Len);
if Len > 0 then
Buffer.Read(Rec.name[1], Len * SizeOf(Char));
Buffer.Read(Len, SizeOf(Len));
SetLength(Rec.add, Len);
if Len > 0 then
Buffer.Read(Rec.add[1], Len * SizeOf(Len));
Buffer.Read(Rec.age, SizeOf(Rec.age));
// TODO: Do stuff with Rec here.
Message.Result := 1;
end else
inherited;
finally
Buffer.Free;
end;
end;
I've used the non-standard TReadOnlyMemoryStream since it makes everything easier. Here's a simple implementation for it:
type
TReadOnlyMemoryStream = class(TCustomMemoryStream)
public
constructor Create(Mem: Pointer; Size: LongInt);
function Write(const Buffer; Count: LongInt): LongInt; override;
end;
constructor TReadOnlyMemoryStream.Create;
begin
inherited Create;
SetPointer(Mem, Size);
end;
function TReadOnlyMemoryStream.Write;
begin
Result := 0;
end;
I have a status which is stored as a string of a set length, either in a file or a database.
I'm looking to enumerate the possible status'
I have the following type to define the possible status'
Type TStatus = (fsNormal = Ord('N'),fsEditedOnScreen = Ord('O'),
fsMissing = Ord('M'),fsEstimated = Ord('E'),fsSuspect = Ord('s'),
fsSuspectFromOnScreen = Ord('o'),fsSuspectMissing = Ord('m'),
fsSuspectEstimated = Ord('e'));
Firstly is this really a good idea? or should I have a seperate const array storing the char conversions? That would mean more than one place to update.
Now convert a string to a status array I have the following, but how can I check if a char is valid without looping through the enumeration?
Function StrToStatus(Value : String):TStatusArray;
var
i: Integer;
begin
if Trim(Value) = '' then
begin
SetLength(Result,0);
Exit;
end;
SetLength(Result,Length(Value));
for i := 1 to Length(Value) do
begin
Result[i] := TStatus(Value[i]); // I don't think this line is safe.
end;
end;
After some testing it sames the suspect line is safe (it doesn't crash!) but just adds in (out of bounds) values which then need filtering out.
Function StrToStatus(Value : String):TStatusArray;
var
i: Integer;
begin
if Trim(Value) = '' then
begin
SetLength(Result,0);
Exit;
end;
SetLength(Result,Length(Value));
for i := 1 to Length(Value) do
begin
Result[i-1] := TStatus(Value[i]);
end;
for i := 0 to Length(Result) - 1 do
begin
case Result[i] of
fsNormal: ;
fsEditedOnScreen: ;
fsMissing: ;
fsEstimated: ;
fsSuspect: ;
fsSuspectFromOnScreen: ;
fsSuspectMissing: ;
fsSuspectEstimated: ;
else
Result [i] := fsNormal;
end;
end;
end;
This allows all the status' and their relative Char values to be in one place and prevents looping through every status for every character in the string. (So in my head atleast should be a bit faster)
AFAIK this should be fine for converting back again.
Function StatusToStr(Value : TStatusArray):String;
var
i: Integer;
begin
for i := 0 to Length(Value) - 1 do
Result := Result + Chr(Ord(Value[i]))
end;
I'm using Delphi 2007
If I understand you correctly I would replace the array with a set and use an enum without explicit values, like so:
program Project1;
{$APPTYPE CONSOLE}
uses
SysUtils;
type
TStatus = (fsNormal, fsEditedOnScreen, fsMissing, fsEstimated, fsSuspect,
fsSuspectFromOnScreen, fsSuspectMissing, fsSuspectEstimated);
TStatusSet = set of TStatus;
const
cStatusChars: array[TStatus] of Char = ('N', 'O', 'M', 'E', 's', 'o', 'm', 'e');
function CharToStatus(AChar: Char; out AStatus: TStatus): Boolean;
var
st: TStatus;
begin
for st := Low(TStatus) to High(TStatus) do
if cStatusChars[st] = AChar then
begin
AStatus := st;
Result := True;
Exit;
end;
Result := False;
end;
function StrToStatus(const Value: string): TStatusSet;
var
i: Integer;
st: TStatus;
begin
Result := [];
for i := 1 to Length(Value) do
if CharToStatus(Value[i], st) then
Include(Result, st);
end;
function StatusToStr(const Value: TStatusSet): string;
var
st: TStatus;
begin
for st in Value do
Result := Result + cStatusChars[st];
end;
var
StatusSet: TStatusSet;
begin
StatusSet := StrToStatus('EmO');
Writeln(StatusToStr(StatusSet));
Readln;
end.
First, I wonder why you save it as string instead of as integer.
The way you've done it, the only way to do it correctly would be to have a Case condition...
function CharToStatus(AChar : Char):TStatus;
begin
case AChar of
'N' : Result := fsNormal;
'O' : Result := fsEditedOnScreen;
'M' : Result := fsMissing;
'E' : Result := fsEstimated;
's' : Result := fsSuspect;
'o' : Result := fsSuspectFromOnScreen;
'm' : Result := fsSuspectMissing;
'e' : Result := fsSuspectEstimated;
else
//Manage error;
end;
end;
function StatusToChar(AStatus : TStatus) : char;
begin
Result := Char(AStatus);
end;
The expression x in [Low(TStatus)]..High(Tstatus)] won't work in this situation.
The reason for this is that Low(TStatus) = 'E', and High(TStatus) = 's'. Anything in-between would be considered valid. (i.e. 'Z' is in [Low(TStatus)]..High(Tstatus)])
The expression x in [Low(TStatus)]..High(Tstatus)] only work on type where there is no "hole" in the declaration. (Like those without explicit values, where the first element is 0, 2nd is 1, 3rd is 2... etc)
//EDIT
Ok.. thinking the problem a bit further, I don't see why you don't like the const array approach... Something like this would be a lot better.
type
TStatus = (fsNormal, fsEditedOnScreen,
fsMissing,fsEstimated,fsSuspect,
fsSuspectFromOnScreen,fsSuspectMissing ,
fsSuspectEstimated);
const
StatusValue : Array[TStatus] of Char = ('N','O','M','E','s','o','m','e');
function StatusValueToTStatus(C : Char) : TStatus;
var I : Integer;
begin
for I := Low(StatusValue) to High(StatusValue) do
begin
if StatusValue = C then
begin
Result := TStatus(I);
EXIT;
end;
end;
//Not found, Manage errors
end;
I'm using Delphi7 (non-unicode VCL), I need to store lots of WideStrings inside a TFileStream. I can't use TStringStream as the (wide)strings are mixed with binary data, the format is projected to speed up loading and writing the data ... However I believe that current way I'm loading/writing the strings might be a bottleneck of my code ...
currently I'm writing length of a string, then writing it char by char ...
while loading, first I'm loading the length, then loading char by char ...
So, what is the fastest way to save and load WideString to TFileStream?
Thanks in advance
Rather than read and write one character at a time, read and write them all at once:
procedure WriteWideString(const ws: WideString; stream: TStream);
var
nChars: LongInt;
begin
nChars := Length(ws);
stream.WriteBuffer(nChars, SizeOf(nChars);
if nChars > 0 then
stream.WriteBuffer(ws[1], nChars * SizeOf(ws[1]));
end;
function ReadWideString(stream: TStream): WideString;
var
nChars: LongInt;
begin
stream.ReadBuffer(nChars, SizeOf(nChars));
SetLength(Result, nChars);
if nChars > 0 then
stream.ReadBuffer(Result[1], nChars * SizeOf(Result[1]));
end;
Now, technically, since WideString is a Windows BSTR, it can contain an odd number of bytes. The Length function reads the number of bytes and divides by two, so it's possible (although not likely) that the code above will cut off the last byte. You could use this code instead:
procedure WriteWideString(const ws: WideString; stream: TStream);
var
nBytes: LongInt;
begin
nBytes := SysStringByteLen(Pointer(ws));
stream.WriteBuffer(nBytes, SizeOf(nBytes));
if nBytes > 0 then
stream.WriteBuffer(Pointer(ws)^, nBytes);
end;
function ReadWideString(stream: TStream): WideString;
var
nBytes: LongInt;
buffer: PAnsiChar;
begin
stream.ReadBuffer(nBytes, SizeOf(nBytes));
if nBytes > 0 then begin
GetMem(buffer, nBytes);
try
stream.ReadBuffer(buffer^, nBytes);
Result := SysAllocStringByteLen(buffer, nBytes)
finally
FreeMem(buffer);
end;
end else
Result := '';
end;
Inspired by Mghie's answer, have replaced my Read and Write calls with ReadBuffer and WriteBuffer. The latter will raise exceptions if they are unable to read or write the requested number of bytes.
There is nothing special about wide strings, to read and write them as fast as possible you need to read and write as much as possible in one go:
procedure TForm1.Button1Click(Sender: TObject);
var
Str: TStream;
W, W2: WideString;
L: integer;
begin
W := 'foo bar baz';
Str := TFileStream.Create('test.bin', fmCreate);
try
// write WideString
L := Length(W);
Str.WriteBuffer(L, SizeOf(integer));
if L > 0 then
Str.WriteBuffer(W[1], L * SizeOf(WideChar));
Str.Seek(0, soFromBeginning);
// read back WideString
Str.ReadBuffer(L, SizeOf(integer));
if L > 0 then begin
SetLength(W2, L);
Str.ReadBuffer(W2[1], L * SizeOf(WideChar));
end else
W2 := '';
Assert(W = W2);
finally
Str.Free;
end;
end;
WideStrings contain a 'string' of WideChar's, which use 2 bytes each. If you want to store the UTF-16 (which WideStrings use internally) strings in a file, and be able to use this file in other programs like notepad, you need to write a byte order mark first: #$FEFF.
If you know this, writing can look like this:
Stream1.Write(WideString1[1],Length(WideString)*2); //2=SizeOf(WideChar)
reading can look like this:
Stream1.Read(WideChar1,2);//assert returned 2 and WideChar1=#$FEFF
SetLength(WideString1,(Stream1.Size div 2)-1);
Stream1.Read(WideString1[1],(Stream1.Size div 2)-1);
You can also use TFastFileStream for reading the data or strings, I pasted the unit at http://pastebin.com/m6ecdc8c2 and a sample below:
program Project36;
{$APPTYPE CONSOLE}
uses
SysUtils, Classes,
FastStream in 'FastStream.pas';
const
WideNull: WideChar = #0;
procedure WriteWideStringToStream(Stream: TFileStream; var Data: WideString);
var
len: Word;
begin
len := Length(Data);
// Write WideString length
Stream.Write(len, SizeOf(len));
if (len > 0) then
begin
// Write WideString
Stream.Write(Data[1], len * SizeOf(WideChar));
end;
// Write null termination
Stream.Write(WideNull, SizeOf(WideNull));
end;
procedure CreateTestFile;
var
Stream: TFileStream;
MyString: WideString;
begin
Stream := TFileStream.Create('test.bin', fmCreate);
try
MyString := 'Hello World!';
WriteWideStringToStream(Stream, MyString);
MyString := 'Speed is Delphi!';
WriteWideStringToStream(Stream, MyString);
finally
Stream.Free;
end;
end;
function ReadWideStringFromStream(Stream: TFastFileStream): WideString;
var
len: Word;
begin
// Read length of WideString
Stream.Read(len, SizeOf(len));
// Read WideString
Result := PWideChar(Cardinal(Stream.Memory) + Stream.Position);
// Update position and skip null termination
Stream.Position := Stream.Position + (len * SizeOf(WideChar)) + SizeOf(WideNull);
end;
procedure ReadTestFile;
var
Stream: TFastFileStream;
my_wide_string: WideString;
begin
Stream := TFastFileStream.Create('test.bin');
try
Stream.Position := 0;
// Read WideString
my_wide_string := ReadWideStringFromStream(Stream);
WriteLn(my_wide_string);
// Read another WideString
my_wide_string := ReadWideStringFromStream(Stream);
WriteLn(my_wide_string);
finally
Stream.Free;
end;
end;
begin
CreateTestFile;
ReadTestFile;
ReadLn;
end.