Hope somebody can help me with this problem - I have to read data from an interface that is specified like this:
<Each message consists of a 2-byte length (in network byte order) followed by that many bytes of data. The end of the msg series is indicated by an empty message (length of 0).>
Using TDataPortTCP I can read the buffer with Dataport.Peek(size) and pull the data from the buffer with Dataport.Pull(size) - both methods provide the result as AnsiStr
I imagine that something like this should work, but I have no idea how to convert AnsiStr to Bytes and vice versa:
while DataPortTCP.Peek(2) > ZeroBytes do
begin
LengthInBytes := DataPortTCP.Pull(2) ;
sContent := DataPortTCP.Pull(LengthInByte) ;
end;
How do I declare / get / convert ZeroBytes and LengthInBytes and how do I have to deal with Endianess ?
Unfortunately I know nothing about TBytes and what I read so far did only lead to more confusion ;-)
I would be very grateful if someone could point me into the right direction.
To check whether a string is not empty, you can compare to ''.
To retrieve the byte value from a string, you can access the character and apply the ord function.
Network order is big endian, mean that the first byte is of higher order. Hence you need to shift it to the left using shl. In this case, there are two bytes, so the first on is shifted 8 bits, which amounts to multiplying it by 256.
var
LengthInBytesStr: String;
LengthInBytes: Word;
begin
...
while DataPortTCP.Peek(2) <> '' do
begin
LengthInBytesStr := DataPortTCP.Pull(2);
LengthInBytes := (ord(LengthInBytesStr[1]) shl 8)
+ ord(LengthInBytesStr[2]);
sContent := DataPortTCP.Pull(LengthInByte);
end;
Related
If I create a subprogram of type function that for instance orders you to type a string of a particular length and you type Overflow, it's supposed to type the last half of the string, so in this case it would be flow. But on the other end if I type an odd number of characters like Stack it's supposed to type the last half of the string + the middle letter, so in this case it would be "ack".
Let me make it clearer (text in bold is user input):
Type a string that's not longer than 7 characters: Candy
The other half of the string is: ndy
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
function Split_String (S : in String) return String is
begin
Mid := 1 + (S'Length / 2);
return S(Mid .. S'Last);
end Split_String;
S : String(1 .. 7);
I : Integer;
begin
Put("Type a string that's no longer than 7 characters: ");
Get_Line(S, I);
Put(Split_String(S));
end Split;
Let me tell you how I've been thinking. So I do a Get_Line to see how many characters the string contains. I then put I in my subprogram to determine if its evenly dividable by two or not. If it's dividable by two, the rest should be 0, thus it'll mean that typing out the other half of the string + THE MIDDLE CHARACTER is not needed. If in all the other cases, it's not dividable by two I have to type out the other half of the string + the middle character. But now I stumbled upon a big problem in my main program. I don't know how type out the other half of a string. If a string contains 4 words I can just type out Put(S(3 .. 4); but the thing is that I don't know a general formula for this. Help is appreciated! :) Have a good day!
You need a more general approach to your problem. Also, try to understand how Get_Line works for you.
For example, if you declare an input string with a large size such as
Input : String (1..1024);
You will have a string large enough to work with any likely input values.
Next, you need a variable to indicate how many characters were actually read by Get_Line.
Length : Natural;
The data returned by Get_Line will then be in the slice of the input string designated as
Input (1 .. Length);
Pass that slice to your function to return the second half of the string.
function last_half(S : string) return string;
last_half(Input(1..Length));
Now all you need is to calculate the last half of the string passed to the function last_half. The function will output a slice of the string passed to it. To find the first index of the last half of the input string you must perform the calculation
mid : Positive := 1 + (S'length / 2);
Then simply return the string S(mid .. S'Last).
It appears that the goal of this exercise is to learn how to use array slices. Concentrate on how slices work for you in the problem and the solution will be very simple.
One possible solution is
with Ada.Text_IO; use Ada.Text_IO;
procedure Main is
Input : String (1 .. 1_024);
Length : Natural;
function last_half (S : in String) return String is
Mid : Positive := 1 + (S'Length / 2);
begin
return S (Mid .. S'Last);
end last_half;
begin
Put ("Enter a string: ");
Get_Line (Input, Length);
Put_Line (Input (1 .. Length) & " : " & last_half (Input (1 .. Length)));
end Main;
Study how the solution uses array slices on the return value of Get_Line and on the parameter for the function last_half and on its return statement. It is also important to remember that the type String is defined as an unbounded array of character. This means that every slice of a string is also a string.
type String is array ( Positive range <> ) of Character;
Aside from being an untidy mess, your latest code edit (as of 20:11 GMT on 15 Nov 2021) doesn’t even compile. Please don’t show us code like this! (unless, of course, that’s the problem).
I’d like to strongly suggest this alternate way of inputting strings:
declare
S : constant String := Get_Line;
begin
-- do things with S, which is exactly as long as
-- the input you typed: no undefined characters at
-- the end to confuse the result, no need to worry
-- about overrunning an input buffer
end;
With this change, and obvious syntactic changes, your current code will do what you want.
4I must write strings to a binary MIDI file. The standard requires one to know the length of the string in bytes. As I want to write for mobile as well I cannot use AnsiString, which was a good way to ensure that the string was a one-byte string. That simplified things. I tested the following code:
TByte = array of Byte;
function TForm3.convertSB (arg: string): TByte;
var
i: Int32;
begin
Label1.Text := (SizeOf (Char));
for i := Low (arg) to High (arg) do
begin
label1.Text := label1.Text + ' ' + IntToStr (Ord (arg [i]));
end;
end; // convert SB //
convertSB ('MThd');
It returns 2 77 84 104 100 (as label text) in Windows as well as Android. Does this mean that Delphi treats strings by default as UTF-8? This would greatly simplify things but I couldn't find it in the help. And what is the best way to convert this to an array of bytes? Read each character and test whether it is 1, 2 or 4 bytes and allocate this space in the array? For converting back to a character: just read the array of bytes until a byte is encountered < 128?
Delphi strings are encoded internally as UTF-16. There was a big clue in the fact that SizeOf(Char) is 2.
The reason that all your characters had ordinal in the ASCII range is that UTF-16 extends ASCII in the sense that characters 0 to 127, in the ASCII range, have the same ordinal value in UTF-16. And all your characters are ASCII characters.
That said, you do not need to worry about the internal storage. You simply convert between string and byte array using the TEncoding class. For instance, to convert to UTF-8 you write:
bytes := TEncoding.UTF8.GetBytes(str);
And in the opposite direction:
str := TEncoding.UTF8.GetString(bytes);
The class supports many other encodings, as described in the documentation. It's not clear from the question which encoding you are need to use. Hopefully you can work the rest out from here.
I am trying to write an Ada equivalent to the split() method in Java or C++. I am to intake a string and an integer and output two seperate string values. For example:
split of "hello" and 2 would return:
"The first part is he
and the second part is llo"
The code I have is as follows:
-- split.adb splits an input string about a specified position.
--
-- Input: Astring, a string,
-- Pos, an integer.
-- Precondition: pos is in Astring'Range.
-- Output: The substrings Astring(Astring'First..Pos) and
-- Astring(Pos+1..Astring'Last).
--------------------------------------------------------------
with Ada.Text_IO, Ada.Integer_Text_IO, Ada.Strings.Fixed;
use Ada.Text_IO, Ada.Integer_Text_IO, Ada.Strings.Fixed;
procedure Split is
EMPTY_STRING : String := " ";
Astring, Part1, Part2 : String := EMPTY_STRING;
Pos, Chars_Read : Natural;
------------------------------------------------
-- Split() splits a string in two.
-- Receive: The_String, the string to be split,
-- Position, the split index.
-- PRE: 0 < Position <= The_String.length().
-- (Ada arrays are 1-relative by default)
-- Passback: First_Part - the first substring,
-- Last_Part - the second substring.
------------------------------------------------
function Split(TheString : in String ; Pos : in Integer; Part1 : out String ; Part2 : out String) return String is
begin
Move(TheString(TheString'First .. Pos), Part1);
Move(TheString(Pos .. TheString'Last), Part2);
return Part1, Part2;
end Split;
begin -- Prompt for input
Put("To split a string, enter the string: ");
Get_Line(Astring, Chars_Read);
Put("Enter the split position: ");
Get(Pos);
Split(Astring, Pos, Part1, Part2);
Put("The first part is ");
Put_Line(Part1);
Put(" and the second part is ");
Put_Line(Part2);
end Split;
The main part I am having trouble with is returning the two separate string values and in general the whole split() function. Any pointers or help is appreciated. Thank you
Instead of a function, consider making Split a procedure having two out parameters, as you've shown. Then decide if Pos is the last index of Part1 or the first index of Part2; I've chosen the latter.
procedure Split(
TheString : in String; Pos : in Integer;
Part1 : out String; Part2 : out String) is
begin
Move(TheString(TheString'First .. Pos - 1), Part1);
Move(TheString(Pos .. TheString'Last), Part2);
end Split;
Note that String indexes are Positive:
type String is array(Positive range <>) of Character;
subtype Positive is Integer range 1 .. Integer'Last;
Doing this is so trivial, I'm not sure why you'd bother making a routine for it. Just about any routine you could come up with is going to be much harder to use anyway.
Front_Half : constant String := Original(Original'first..Index);
Back_Half : constant String := Original(Index+1..Original'last);
Done.
Note that static Ada strings are very different than strings in other languages like C or Java. Due to their static nature, they are best built either inline like I've done above, or as return values from functions. Since functions cannot return more than one value, a single unified "split" routine is just plain not a good fit for static Ada string handling. Instead, you should either do what I did above, call the corresponding routines from Ada.Strings.Fixed (Head and Tail), or switch to using Ada.Strings.Unbounded.Unbounded_String instead of String.
The latter is probably the easiest option, if you want to keep your Java mindset about string handling. If you want to really learn Ada though, I'd highly suggest you learn to deal with static fixed Strings the Ada way.
From looking over your code you really need to read up in general on the String type, because you're dragging in a lot of expectations in from other languages on how to work with them--which aren't going to work with them. Ada's String type is not one of its more flexible features, in that they are always fixed length. While there are ways of working around the limitations in a situation such as you're describing, it would be much easier to simply use Unbounded_Strings.
The input String to your function could remain of type String, which will adjust to the length of the string that you provide to it. The two output Unbounded_Strings then are simply set to the sliced string components after invoking To_Unbounded_String() on each of them.
Given the constraints of your main program, with all strings bounded by the size of EMPTY_STRING. the procedure with out parameters is the correct approach, with the out parameter storage allocated by the caller (on the stack as it happens)
That is not always the case, so it is worth knowing another way. The problem is how to deal with data whose size is unknown until runtime.
Some languages can only offer runtime allocation on the heap (via "new" or "malloc") and can only access the data via pointers, leaving a variety of messy problems including accesses off the end of the data (buffer overruns) or releasing the storage correctly (memory leaks, accessing freed pointers etc)
Ada will allow this method too, but it is usually unnecessary and strongly discouraged. Unbounded_String is a wrapper over this method, while Bounded_String avoids heap allocation where you can accept an upper bound on the string length.
But also, Ada allows variable sized data structures to be created on the stack; the technique just involves creating a new stack frame and declaring new variables where you need to, with "declare". The new variables can be initialised with function calls.
Each function can only return one object, but that object's size can be determined at runtime. So either "Split" can be implemented as 2 functions, returning Part1 or Part2, or it can return a record containing both strings. It would be a record with two size discriminants, so I have chosen the simpler option here. The function results are usually built in place (avoids copying).
The flow in your example would require two nested Declare blocks; if "Pos" could be identified first, they could be collapsed into one...
procedure Split is
function StringBefore( Input : String; Pos : Natural) return String is
begin
return Input(1 .. Pos-1);
end StringBefore;
function StringFrom ...
begin
Put("To split a string, enter the string: ");
declare
AString : String := Get_Line;
Pos : Natural;
begin
Put("Enter the split position: ");
Get(Pos);
declare
Part1 : String := StringBefore(AString, Pos);
Part2 : String := StringFrom(AString, Pos);
begin
Put("The first part is ");
Put_Line(Part1);
Put(" and the second part is ");
Put_Line(Part2);
end; -- Part1 and Part2 are now out of scope
end; -- AString is now out of scope
end Split;
This can obviously be wrapped in a loop, with different size strings each time, with no memory management issues.
Look at the Head and Tail functions in Ada.Strings.Fixed.
function Head (Source : in String; Count : in Natural; Pad : in Character := Space) return String;
function Tail (Source : in String; Count : in Natural; Pad : in Character := Space)
return String;
Here's an approach that just uses slices of the string.
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Strings.Fixed; use Ada.Strings.Fixed;
procedure Main is
str : String := "one,two,three,four,five,six,seven,eight";
pattern : String := ",";
idx, b_idx : Integer;
begin
b_idx := 1;
for i in 1..Ada.Strings.Fixed.Count ( Source => str, Pattern => pattern ) loop
idx := Ada.Strings.Fixed.Index( Source => str(b_idx..str'Last), Pattern => pattern);
Put_Line(str(b_idx..idx-1)); -- process string slice in any way
b_idx := idx + pattern'Length;
end loop;
-- process last string
Put_Line(str(b_idx..str'Last));
end Main;
im working on delphi 7 and i was working on a strings, i came across this
For a string of default length, that is, declared simply as string, max size is always 255. A ShortString is never allowed to grow to more than 255 characters.
on delphi strings
once i had to do something like this in my delphi code (that was for a really big query)
var
sMyStringOF256characters : string;
ilength : integer;
begin
sMyStringOF256characters:='ThisStringisofLength256,ThisStringisofLength256,.....'
//length of sMyStringOF256characters is 256
end;
i get this error
[Error] u_home.pas(38): String literals may have at most 255 elements.
but when i try this
var
iCounter : integer;
myExtremlyLongString : string;
begin
myExtremlyLongString:='';
Label1.Caption:='';
for iCounter:=0 to 2500 do
begin
myExtremlyLongString:=myExtremlyLongString+inttostr(iCounter);
Label1.Caption:=myExtremlyLongString;
end;
Label2.Caption:=inttostr(length(myExtremlyLongString));
end;
and the result is
As you can see the length of myExtremlyLongString is 8894 characters.
why did not delphi give any error saying the length is beyond 255 for myExtremlyLongString?
EDIT
i used
SetLength(sMyStringOF256characters,300);
but it doesnt work.
why did not delphi give any error saying the length is beyond 255 for
myExtremlyLongString?
You have your answer a bit down in the text in section Long String (AnsiString).
In current versions of Delphi, the string type is simply an alias for
AnsiString,
So string is not limited to 255 characters but a string literal is. That means that you can build a string that is longer than 255 characters but you can not have a string value in code that is longer than 255 characters. You need to split them if you want that.
sMyString:='ThisStringisofLength255'+'ThisStringisofLength255';
Split it up into:
sMyStringOF256characters :=
'ThisStringis' +
'ofLength256' +
'And ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'ManyManyManyManyManyManyManyManyManyManyManyManyMany' +
'CharactersCharactersCharactersCharactersCharactersCharactersCharactersCharacters';
Back in old DOS/Turbo Pascal days, "strings" were indeed limited to 255 characters. In large part because the 1st byte contained the string length, and a byte can only have a value between 0 and 255.
That is no longer an issue in contemporary versions of Delphi.
"ShortString" is the type for the old DOS/Pascal string type.
"LongString" has been the default string type for a long time (including the Borland Delphi 2006 I currently use for most production work). LongStrings (aka "AnsiStrings") hold 8-bit characters, and are limited only by available memory.
Recent versions of Delphi (Delphi 2009 and higher, including the new Delphi XE2) all now default to multi-byte Unicode "WideString" strings. WideStrings, like AnsiStrings, are also effectively "unlimited" in maximum length.
This article explains in more detail:
http://delphi.about.com/od/beginners/l/aa071800a.htm
The difference is that in your first code example you are putting the string as part of your code - literal string. That has a limitation on how many characters it will allow.
In your second code example you are generating it dynamically and not putting it as one big literal string.
String type in Delphi (unlike shortstring that can only be up to 255) can be as big as your memory.
You could try using the StringBuilder class:
procedure TestStringBuilder;
var
I: Integer;
StringBuilder: TStringBuilder;
begin
StringBuilder := TStringBuilder.Create;
try
for I := 1 to 10 do
begin
StringBuilder.Append('a string ');
StringBuilder.Append(66); //add an integer
StringBuilder.Append(sLineBreak); //add new line
end;
OutputWriteLine('Final string builder length: ' + IntToStr(StringBuilder.Length));
finally
StringBuilder.Free;
end;
end;
If you need realy long string in Delphi, you can load it from other resources like a txt files or just plain text with any extension. Im using it and it works. You can create "like a" array tables using plain text lines numbers. In delphi code, you can do as #arjen van der Spek and others says only.
For me, files with text as var's formated -
sometext:string=
'txt...'+
'txt...'+
'txt...';
are bad for future editing.
pros: you can use any long text.
cons: text code is open, anybody can read it opening file in notepad etc.
I've just encountered a weird problem. I am trying to load a model to OpenGL and in the part where I load textures I use auxDIBImageLoadA(dibfile:PWideChar) function. Here is my code calling it
procedure CreateTexture(var textureArray: array of UINT; strFileName: string; textureID: integer); // Vytvožení textury
var
pBitmap: PTAUX_RGBImageRec;
begin
if strFileName = '' then exit;
MessageBox(0,PWideChar(strFileName),nil,SW_SHOWNORMAL);
pBitmap := auxDIBImageLoadA(PWideChar(strFileName));
if pBitmap = nil then exit;
...
The MessageBox is just for control. This is what happens: I run the application, a box with "FACE.BMP" appears. Okay. But then I get an error saying "Failed to open DIB file F". When i set the stFileName to xFACE.BMP, I get an "Failed to open DIB file x". So for some reason it appears that the function is taking only the first char.
Am I missing something? I'm using glaux.dll which I downloaded like 5 times from different sources, so it should be bug-free (I hope, every OpenGL site referred to it).
That's odd, functions ending in "A" generally take PAnsiChar pointers, and those ending in "W" take PWideChar pointers. Is there a auxDIBImageLoadW call also? If there is use that one, or try with PAnsiChar, since the PWideChar you pass (two bytes per position) would look like a string one character long if it is evaluated as a 1-byte string.
You need to convert your Unicode string to ANSI. Do it like this
pBitmap := auxDIBImageLoadA (PAnsiChar(AnsiString(strFileName)))
You would be better off calling the Unicode version though
pBitmap := auxDIBImageLoadW (PWideChar(strFileName))