I am trying to read two strings of varying length from a TMemoryStream, but both streams end up being the same length. So if, for example, the first string is 'abcdefghijkl', and the second one is 'wxyz', the value I get for the second string is 'wxyzefghijkl' (the first four characters of my new string ('wxyz') followed by the remaining characters of the 1st string that have not been replaced by 'wxyz'
My code is:-
var
L : LongInt
S : string;
...
msRecInfo.Position := 0;
msRecInfo.Read(L, SizeOf(L)); // read size of following string ...
SubStream.Clear;
SubStream.CopyFrom(msRecInfo, L); // copy next block of data to a second TMemoryStream
if (L > 0) then S := StreamToString(SubStream); //convert the stream into a string
msRecInfo.Read(L, SizeOf(L)); // get size of following string ...
SubStream.CopyFrom(msRecInfo, L);
if (L > 0) then S := StreamToString(SubStream);
I have been battling with this for hours without success. Can anyone point out what I am doing wrong?
You are not calling SubStream.Clear() before the 2nd call to SubStream.CopyFrom(). So, the 1st call to StreamToString(SubStream) leaves SubStream.Position at the end of the stream, then the subsequent SubStream.CopyFrom() adds more data to the stream, preserving the existing data. Then the subsequent StreamToString(SubStream) reads all of the data from SubStream.
Also, be aware that if L is 0 when you pass it to SubStream.CopyFrom(), it will copy the entire msRecInfo stream. This is documented behavior:
https://docwiki.embarcadero.com/Libraries/en/System.Classes.TStream.CopyFrom
If Count is 0, CopyFrom sets Source position to 0 before reading and then copies the entire contents of Source into the stream. If Count is greater than or less than 0, CopyFrom reads from the current position in Source.
So, you need to move up your L > 0 check, eg:
msRecInfo.Read(L, SizeOf(L));
if (L > 0) then
begin
SubStream.Clear;
SubStream.CopyFrom(msRecInfo, L);
S := StreamToString(SubStream);
end
else
S := '';
I would suggest wrapping this logic into a reusable function, eg:
var
L : LongInt;
S : string;
function ReadString: string;
begin
msRecInfo.Read(L, SizeOf(L)); // read size of following string ...
if (L > 0) then
begin
SubStream.Clear;
SubStream.CopyFrom(msRecInfo, L); // copy next block of data to a second TMemoryStream
Result := StreamToString(SubStream); //convert the stream into a string
end else
Result := '';
end;
begin
...
msRecInfo.Position := 0;
S := ReadString;
S := ReadString;
...
Although, if feasible, I would suggest just getting rid of SubStream altogether, update StreamToString() to take L as an input parameter, so that you can read the string from msRecInfo directly, eg:
msRecInfo.Read(L, SizeOf(L));
S := StreamToString(msRecInfo, L);
No need for a 2nd TMemoryStream if you can avoid it.
Related
Suppose this string:
uses Windows, Messages, SysUtils, {-} uCustom1, uCustom2, uCustom3;
how capture all after {-} without know a fixed lenght to delete to left side? problably RightStr could help, but this require a lenght on second parameter that i not know how obtain automatically (that is all until {-} in this case). Some idea?
I usually use this function:
function TailOf(const Input, Delimiter : String) : String;
var
P : Integer;
begin
P := Pos(Delimiter, Input);
if P > 0 then
Result := Copy(Input, P + Length(Delimiter), MaxInt)
else
Result := '';
end;
var
S : String;
S := 'ab{cd}def';
S := TailOf(S, '{cd}');
// S now = 'def'
Pos and Copy are standard RTL functions which you can look up in the OLH.
I also have a complementary function, HeadOf, which returns the contents of a string up to but not including the delimiter, or the whole string if the delimiter is not found.
This is something that should be easey but I just can´t get it work.
I come from java so maby I have a error in my thinking here.
What I want to do is that I have a string with two letters like 't4' or 'pq'.
Now I just want to get each of the chracters in the string as an own string.
So I do:
firstString := myString[0];
but I don´t even get this compiled.
So I figured that they start counting form 1 and put 1 as an index.
Now I do this in a while loop and the first time I go through it it works fine. Then the second time the results are just empty or wrong numbers.
What am I missing here?
(I also tried copy but that doesn´t work either!)
while i < 10 do
begin
te := 'te';
a := te[1];
b := te[2];
i := i +1;
end;
the first loop a is 't' and b is 'e' as I would expect. The second time a is '' and b ist 't' which I don´t understand!
Strings are 1-based, not zero-based. Try the following, after adding StrUtils to your Uses list (for DupeString):
var
MyString : String;
begin
MyString := '12345';
Caption := StringOfChar(MyString[1], 8) + ':' + DupeString(Copy(MyString, 3, 2), 4);
You could split it up to mke it easier to follow, of course:
var
MyString,
S1,
S2,
S3: String;
begin
MyString := '12345';
S1 := StringOfChar(MyString[1], 8);
S2 := Copy(MyString, 3, 2);
S3 := DupeString(S2, 4);
Caption := S1 + ':' + S3;
Problem
There are multiple ways to store string reference, so how would you do it in the example code? Currently the problem is with storing access to string because it is causing non-local pointer cannot point to local object. Is storing 'First and 'Last to reference a string a preferable way?
String reference storage
This record stores reference to a string. The First and Last is supposed to point to a string. The Name should be able to the same I think, but that will cause non-local pointer cannot point to local object when a local string is assigned to that. So the current work around solution is to use First and Last.
type Segment is record
First : Positive;
Last : Positive;
Length : Natural := 0;
Name : access String;
end record;
Assigning sub string reference
The commented line is causing non-local pointer cannot point to local object. This is because Item is local. Source is not local and that is the string I want sub string references from.
procedure Find (Source : aliased String; Separator : Character; Last : out Natural; Item_Array : out Segment_Array) is
P : Positive := Source'First;
begin
for I in Item_Array'Range loop
declare
Item : aliased String := Separated_String_Next (Source, Separator, P);
begin
exit when Item'Length = 0;
Item_Array (I).Length := Item'Length;
Item_Array (I).First := Item'First;
Item_Array (I).Last := Item'Last;
--Item_Array (I).Name := Item'Access;
Last := I;
end;
end loop;
end;
Example
with Ada.Text_IO;
with Ada.Integer_Text_IO;
procedure Main is
use Ada.Text_IO;
use Ada.Integer_Text_IO;
function Separated_String_Next (Source : String; Separator : Character; P : in out Positive) return String is
A : Positive := P;
B : Positive;
begin
while A <= Source'Last and then Source(A) = Separator loop
A := A + 1;
end loop;
P := A;
while P <= Source'Last and then Source(P) /= Separator loop
P := P + 1;
end loop;
B := P - 1;
while P <= Source'Last and then Source(P) = Separator loop
P := P + 1;
end loop;
return Source (A .. B);
end;
type Segment is record
First : Positive;
Last : Positive;
Length : Natural := 0;
Name : access String;
end record;
type Segment_Array is array (Integer range <>) of Segment;
procedure Find (Source : String; Separator : Character; Last : out Natural; Item_Array : out Segment_Array) is
P : Positive := Source'First;
begin
for I in Item_Array'Range loop
declare
Item : aliased String := Separated_String_Next (Source, Separator, P);
begin
exit when Item'Length = 0;
Item_Array (I).Length := Item'Length;
Item_Array (I).First := Item'First;
Item_Array (I).Last := Item'Last;
--Item_Array (I).Name := Item'Access;
Last := I;
end;
end loop;
end;
Source : String := ",,Item1,,,Item2,,Item3,,,,,,";
Item_Array : Segment_Array (1 .. 100);
Last : Natural;
begin
Find (Source, ',', Last, Item_Array);
Put_Line (Source);
Put_Line ("Index First Last Name");
for I in Item_Array (Item_Array'First .. Last)'Range loop
Put (I, 5);
Put (Item_Array (I).First, 6);
Put (Item_Array (I).Last, 5);
Put (" ");
Put (Source (Item_Array (I).First .. Item_Array (I).Last));
New_Line;
end loop;
end;
Output
,,Item1,,,Item2,,Item3,,,,,,
Index First Last Name
1 3 7 Item1
2 11 15 Item2
3 18 22 Item3
The error message tells you exactly what is wrong : Item is a string declared locally, i.e. on the stack, and you are assigning its address to an access type (pointer). I hope I don't need to explain why that won't work.
The immediate answer - which isn't wrong but isn't best practice either, is to allocate space for a new string - in a storage pool or on the heap - which is done with new.
Item : access String := new String'(Separated_String_Next (Source, Separator, P));
...
Item_Array (I).Name := Item;
Note that some other record members, at least, Length all appear to be completely redundant since it is merely a copy of its eponymous attributes, so should probably be eliminated (unless there's a part of the picture I can't see).
There are better answers. Sometimes you need to use access types, and handle their object lifetimes and all the ways they can go wrong. But more often their appearance is a hint that something in the design can be improved : for example:
the Unbounded_String may manage your strings more simply
You could use the length as a discriminant on the Segment record, and store the actual string (not an Access) in the record itself
Ada.Containers are a standard library of containers to abstract over handling the storage yourself (much as the STL is used in C++).
If you DO decide you need access types, it's better to use a named access type type Str_Access is access String; - then you can create a storage pool specific to Str_Acc types, and release the entire pool in one operation, to simplify object lifetime management and eliminate memory leaks.
Note the above essentially "deep copies" the slices of the Source string. If there is a specific need to "shallow copy" it - i.e. refer to the specific substrings in place - AND you can guarantee its object lifetime, this answer is not what you want. If so, please clarify the intent of the question.
For a "shallow copy" the approach in the question essentially fails because Item is already a deep copy ... on the stack.
The closest approach I can see is to make the source string aliassed ... you MUST do as you want each Segment to refer to it ... and pass its access to the Find procedure.
Then each Segment becomes a tuple of First, Last, (redundant Length) and access to the entire string (rather than a substring).
procedure Find (Source : access String; Separator : Character;
Last : out Natural; Item_Array : out Segment_Array) is
P : Positive := Source'First;
begin
for I in Item_Array'Range loop
declare
Item : String := Separated_String_Next (Source.all, Separator, P);
begin
exit when Item'Length = 0;
...
Item_Array (I).Name := Source;
Last := I;
end;
end loop;
end;
Source : aliased String := ",,Item1,,,Item2,,Item3,,,,,,";
...
Find (Source'access, ',', Last, Item_Array);
for I in Item_Array (Item_Array'First .. Last)'Range loop
...
Put (Item_Array (I).Name(Item_Array (I).First .. Item_Array (I).Last));
New_Line;
end loop;
A helper to extract a string from a Segment would probably be useful:
function get(S : Segment) return String is
begin
return S.Name(S.First .. S.Last);
end get;
...
Put (get(Item_Array (I));
The only rationale I can see for such a design is where the set of strings to be parsed or dissected will barely fit in memory so duplication must be avoided. Perhaps also embedded programming or some such discipline where dynamic (heap) allocation is discouraged or even illegal.
I see no solution involving address arithmetic within a string, since an array is not merely its contents - if you point within it, you lose the attributes. You can make the same criticism of the equivalent C design : you can identify the start of a substring with a pointer, but you can't just stick a null terminator at the end of the substring without breaking the original string.
Given the bigger picture ... what you need, rather than the low level details of how you want to achieve it, there are probably better solutions.
The program has several "encryption" algorithms. This one should blockwise reverse the input. "He|ll|o " becomes "o |ll|He" (block length of 2).
I add two strings, in this case appending the result string to the current "block" string and making that the result. When I add the result first and then the block it works fine and gives me back the original string. But when i try to reverse the order it just gives me the the last "block".
Several other functions that are used for "rotation" are above.
//amount of blocks
function amBl(i1:integer;i2:integer):integer;
begin
if (i1 mod i2) <> 0 then result := (i1 div i2) else result := (i1 div i2) - 1;
end;
//calculation of block length
function calcBl(keyStr:string):integer;
var i:integer;
begin
result := 0;
for i := 1 to Length(keyStr) do
begin
result := (result + ord(keyStr[i])) mod 5;
result := result + 2;
end;
end;
//desperate try to add strings
function append(s1,s2:string):string;
begin
insert(s2,s1,Length(s1)+1);
result := s1;
end;
function rotation(inStr,keyStr:string):string;
var //array of chars -> string
block,temp:string;
//position in block variable
posB:integer;
//block length and block count variable
bl, bc:integer;
//null character as placeholder
n : ansiChar;
begin
//calculating block length 2..6
bl := calcBl(keyStr);
setLength(block,bl);
result := '';
temp := '';
{n := #00;}
for bc := 0 to amBl(Length(inStr),bl) do
begin
//filling block with chars starting from back of virtual block (in inStr)
for posB := 1 to bl do
begin
block[posB] := inStr[bc * bl + posB];
{if inStr[bc * bl + posB] = ' ' then block[posB] := n;}
end;
//adding the block in front of the existing result string
temp := result;
result := block + temp;
//result := append(block,temp);
//result := concat(block,temp);
end;
end;
(full code http://pastebin.com/6Uarerhk)
After all the loops "result" has the right value, but in the last step (between "result := block + temp" and the "end;" of the function) "block" replaces the content of "result" with itself completely, it doesn't add result at the end anymore.
And as you can see I even used a temp variable to try to work around that.. doesnt change anything though.
I am 99.99% certain that your problem is due to a subtle bug in your code. However, your deliberate efforts to hide the relevant code mean that we're really shooting in the dark. You haven't even been clear about where you're seeing the shortened Result: GUI Control/Debugger/Writeln
The irony is that you have all the information at your fingertips to provide a small concise demonstration of your problem - including sample input and expected output.
So without the relevant information, I can only guess; I do think I have a good hunch though.
Try the following code and see if you have a similar experience with S3:
S1 := 'a'#0;
S2 := 'bc';
S3 := S1 + S2;
The reason for my hunch is that #0 is a valid character in a string: but whenever that string needs to be processed as PChar, #0 will be interpreted as a string terminator. This could very well cause the "strange behaviour" you're seeing.
So it's quite probable that you have at least one of the following 2 bugs in your code:
You are always processing 1 too many characters; with the extra character being #0.
When your input string has an odd number of characters: your algorithm (which relies on pairs of characters) adds an extra character with value #0.
Edit
With the additional source code, my hunch is confirmed:
Suppose you have a 5 character string, and key that produces block length 2.
Your inner loop (for posB := 1 to bl do) will read beyond the length of inStr on the last iteration of the outer loop.
So if the next character in memory happens to be #0, you will be doing exactly as described above.
Additional problem. You have the following code:
//calculating block length 2..6
bl := calcBl(keyStr);
Your assumption in the comment is wrong. From the implementation of calcBl, if keyStr is empty, your result will be 0.
I am trying to get a particular integer after a sub string in InnoSetup in a line. There are Trim, TrimLeft, TrimRight functions but no substring extraction functions.
Example :
line string: 2345
line another string: 3456
I want to extract "2345" and "3456".
I am loading the file content in a array but can't get it de-referenced by array[count][char_count].
I would load the input file to a TStrings collection and iterate it line by line. For each line I would find a ":" char position and from this position I would copy the string which I would finally trim. In steps:
1. line string: 2345
2. 2345
3. 2345
Now remains to convert such string to an integer and add it to the final collection. Since you've shown an empty line in your file sample, and since you didn't said if this format will always be fixed, let's convert this string in the safe way. Inno Setup provides for this safe conversion just one function, the StrToIntDef function. This function however requires a default value, which is returned when the conversion fails and so you will have to pass to its call a value, which you'll never expect in your file. In the following example I chose -1, but you can replace it with any other value that you never expect in your input file:
[Code]
type
TIntegerArray = array of Integer;
procedure ExtractIntegers(Strings: TStrings; out Integers: TIntegerArray);
var
S: string;
I: Integer;
Value: Integer;
begin
for I := 0 to Strings.Count - 1 do
begin
// trim the string copied from a substring after the ":" char
S := Trim(Copy(Strings[I], Pos(':', Strings[I]) + 1, MaxInt));
// try to convert the value from the previous step to integer;
// if such conversion fails, because the string is not a valid
// integer, it returns -1 which is treated as unexpected value
// in the input file
Value := StrToIntDef(S, -1);
// so, if a converted value is different from unexpected value,
// add the value to the output array
if Value <> -1 then
begin
SetArrayLength(Integers, GetArrayLength(Integers) + 1);
Integers[GetArrayLength(Integers) - 1] := Value;
end;
end;
end;
procedure InitializeWizard;
var
I: Integer;
Strings: TStringList;
Integers: TIntegerArray;
begin
Strings := TStringList.Create;
try
Strings.LoadFromFile('C:\File.txt');
ExtractIntegers(Strings, Integers);
for I := 0 to GetArrayLength(Integers) - 1 do
MsgBox(IntToStr(Integers[I]), mbInformation, MB_OK);
finally
Strings.Free;
end;
end;