I am trying to learn iOs programming. and I suppose this is a bit of a reverse question.
I have just completed a tutorial on youtube using Xcode to create a simple iPhone app that will allow you to store, list and delete data from an SQLite3 database (as the app i want to produce will need a database).
However the bloke who put the video up didn't seem to explain 'why' he did what he did, so I am now trying to understand what each bit of code does
(I come from a PHP and SQL web programming background, so I understand accessing databases, calling data rows etc to show the content on a website.)
The one part of this iOs bit I don't quite understand is the %s and %d values used as they didn't seem to be declared anywhere.
The code is;
if(sqlite3_open([dbPathString UTF8String], &personDB)==SQLITE_OK) {
NSString *inserStmt = [NSString stringWithFormat:#"INSERT INTO PERSONS(NAME,AGE) values ('%s', '%d')",[self.nameField.text UTF8String],[self.ageField.text intValue]];
now %s and %d clearly get their values from the self.nameField and self.ageField. However that implies that I could only ever submit two values into a table? or are there other % for other values, but surely then there is a max of 26.
I would be grateful for any explanation you could give.
Also in addition, does anyone have any suggestions about other fully explained ways to learn to code for iOS? especially if you were a starter just learning iOS programming for a first time with limited C programming skills before hand.
The area i am looking for is to create an app that will store some text fields and an image, which either will be stored in a database and the image either in the database or as a link and appropriately named.
I'd like to be able to manipulate the image to resize it so it is optimised for the iPhone display (don't need a HD image in the APP)
Later I'd like to be able to work out how either upload the local database (sqlite3) file to a an online storage (either my own server or dropbox), or synchronise it to an SQL database (from initial looks just exporting the file would be better and embedding the images into a field would be better for this project, even though i know it is not the normal way of doing things)
%s and %d are format specifiers for a null-terminated array of characters and a signed 32-bit integer respectively. You can find the details about specifiers in the String Programming Guide. However, you should not format the string this way for a SQLite statement as it puts you at risk of SQL injection. Instead you should bind the values using ? and the appropriate sqlite3_bind* function. For your situation you would use sqlite3_bind_text for NAME and sqlite3_bind_int for AGE.
Have a look at the class reference:
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html
Here are the string format specifiers:
https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265
As you can see, %d is outputting an integer while %s is outputting a string.
Part 1:
The % convention "string format specifiers" is a common standard for string substitution.
They are not variables, but typed substitution placeholders.
%s --> string
%d --> number
Part 2:
You might check out the iTunes U course:
iPhone Application Programming '11
by Prof. Jan Borchers
https://itunes.apple.com/us/itunes-u/iphone-application-programming/id474416629
https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html
%s
Null-terminated array of 8-bit unsigned characters. Because the %s specifier causes the characters to be interpreted in the system default encoding, the results can be variable, especially with right-to-left languages. For example, with RTL, %s inserts direction markers when the characters are not strongly directional. For this reason, it’s best to avoid %s and specify encodings explicitly.
%d, %D
Signed 32-bit integer (int).
That is what is called a formatted string, basically, it is a way to inject values into a string. The character after the % sign is used to indicate the datatype that the value should be formatted as. In your case, %s is used to indicate a string value and %d is used to indicate a decimal integral value.
This type of string formatting is extremely common; many programming languages provide some mechanism for performing this type of string formatting and the formatting symbols are largely standardized. You can find a more information on the C++ website.
Related
I have a string that, by using string.format("%02X", char), I've received the following:
74657874000000EDD37001000300
In the end, I'd like that string to look like the following:
t e x t NUL NUL NUL í Ó p SOH NUL ETX NUL (spaces are there just for clarification of characters desired in example).
I've tried to use \x..(hex#), string.char(0x..(hex#)) (where (hex#) is alphanumeric representation of my desired character) and I am still having issues with getting the result I'm looking for. After reading another thread about this topic: what is the way to represent a unichar in lua and the links provided in the answers, I am not fully understanding what I need to do in my final code that is acceptable for this to work.
I'm looking for some help in better understanding an approach that would help me to achieve my desired result provided below.
ETA:
Well I thought that I had fixed it with the following code:
function hexToAscii(input)
local convString = ""
for char in input:gmatch("(..)") do
convString = convString..(string.char("0x"..char))
end
return convString
end
It appeared to work, but didnt think about characters above 127. Rookie mistake. Now I'm unsure how I can get the additional characters up to 256 display their ASCII values.
I did the following to check since I couldn't truly "see" them in the file.
function asciiSub(input)
input = input:gsub(string.char(0x00), "<NUL>") -- suggested by a coworker
print(input)
end
I did a few gsub strings to substitute in other characters and my file comes back with the replacement strings. But when I ran into characters in the extended ASCII table, it got all forgotten.
Can anyone assist me in understanding a fix or new approach to this problem? As I've stated before, I read other topics on this and am still confused as to the best approach towards this issue.
The simple way to transform a base16-encoded string is just to
function unhex( input )
return (input:gsub( "..", function(c)
return string.char( tonumber( c, 16 ) )
end))
end
This is basically what you have, just a bit cleaner. (There's no need to say "(..)", ".." is enough – if you specify no captures, you'll automatically get the whole match. And while it might work if you write string.char( "0x"..c ), it's just evil – you concatenate lots of strings and then trigger the automatic conversion to numbers. Much better to just specify the base when explicitly converting.)
The resulting string should be exactly what went into the hex-dumper, no matter the encoding.
If you cannot correctly display the result, your viewer will also be unable to display the original input. If you used different viewers for the original input and the resulting output (e.g. a text editor and a terminal), try writing the output to a file instead and looking at it with the same viewer you used for the original input, then the two should be exactly the same.
Getting viewers that assume different encodings (e.g. one of the "old" 8-bit code pages or one of the many versions of Unicode) to display the same thing will require conversion between different formats, which tends to be quite complicated or even impossible. As you did not mention what encodings are involved (nor any other information like OS or programs used that might hint at the likely encodings), this could be just about anything, so it's impossible to say anything more specific on that.
You actually have a couple of problems:
First, make sure you know the meaning of the term character encoding, and that you know the difference between characters and bytes. A popular post on the topic is The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)
Then, what encoding was used for the bytes you just received? You need to know this, otherwise you don't know what byte 234 means. For example it could be ISO-8859-1, in which case it is U+00EA, the character ê.
The characters 0 to 31 are control characters (eg. 0 is NUL). Use a lookup table for these.
Then, displaying the characters on the terminal is the hard part. There is no platform-independent way to display ê on the terminal. It may well be impossible with the standard print function. If you can't figure this step out you can search for a question dealing specifically with how to print Unicode text from Lua.
Considering this Arabic word(جبل) made of 3 letters .
-the first letter is جـ,
-name is (ǧīm),
-its Unicode value is FE9F when its in the beginning,
-its basic value is 062C and
-its isolated value is FE9D but the last two values return the same shape drawing ج .
Now, Whenever I try to get it as a single character -trying many different ways-, Delphi returns the basic Unicode value.
well,that makes sense,but what happens to the char with transformation? It is a single char too..Looks like it takes the transformed value only when it is within a string, but where? how to extract it?When and which process decides these values?
Again the MAIN QUESTION:
How can I get the Arabic letter or its Unicode value as it is within a string?
just for information: Unlike English which has tow cases for its letters(Capital and Small), Arabic has four cases(Isolated, Beginning,Middle And End) with different rules as well.
I'm not sure I understand the question. If you want to know how to write U+FE9F in Delphi source code, in a modern Unicode version of Delphi. Do that simply like so:
Char($FE9F)
If you want to read individual characters from جبل then do it like this:
const
MyWord = 'جبل';
var
c: Char;
....
c := MyWord[1];//this is U+062C
Note that the code above is fine for your particular word because each code point can be encoded with a single UTF-16 WideChar character element. If the code point required multiple elements, then it would be best to transform to UTF-32 for code point level processing.
Now, let's look at the string that you included in the question. I downloaded this question using wget and the file that came down the wires was UTF-8 encoded. I used Notepad++ to convert to UTF16-LE and then picked out the three UTF-16 characters of your string. They are:
U+062C
U+0628
U+0644
You stated:
The first letter is جـ, name is (ǧīm), its Unicode value is U+FE9F.
But that is simply incorrect. As can be seen from the above, the actual character you posted was U+062C. So the reason why your attempts to read the first character yield U+062C is that U+062C really is the first character of your string.
The bottom line is that nothing in your Delphi code is transforming your character. When you do:
S[1] := Char($FE9F);
the compiler performs a simple two byte copy. There is no context aware transformation that occurs. And likewise when reading S[1].
Let's look at how these characters are displayed, using this simple code on a VCL forms application that contains a memo control:
Memo1.Clear;
Memo1.Lines.Add(StringOfChar(Char($FE9F), 2));
Memo1.Lines.Add(StringOfChar(Char($062C), 2));
The output looks like this:
As you can see, the rendering layer knows what to do with a U+062C character that appears at the beginning of the string.
Shaping of Arabic characters for presentation in Windows is served by the Uniscribe services (USP10.dll).
UniScribe
You may find the following blog post useful:
Roozbeh's Programming Blog
I don't think you can do it using string/char related methods. But using pchar, maybe can you access the memory and read the Pword values directly
EDIT: After discussing with David, I think that you will always get the basic/isolated value of the letter. The fact that begin or end glyph is used, is probably just handled by the display framework of the OS
As already pointed out in the topic, I got the following error:
Character #\u009C cannot be represented in the character set CHARSET:CP1252
trying to print out a string given back by drakma:http-request, as far as I understand the error-code the problem is that the windows-encoding (CP1252) does not support this character.
Therefore to be able to process it, I might/must convert the whole string.
My question is what package/library does support converting strings to certain character-sets efficiently?
An alike question is this one, but just ignoring the error would not help in my case.
Drakma already does the job of "converting strings": after all, when it reads from some random webserver, it just gets a stream of bytes. It then has to convert that to a lisp string. You probably want to bind *drakma-default-external-format* to something else, although I can't remember off-hand what the allowable values are. Maybe something like :utf-8?
I'm having a strange problem that is affecting at least some of my international users of my Delphi 6 application. Here's the scenario:
My program requests status reports periodically from an external device that acts as an HTTP server.
The device sends back the status report as a response document that has a series fields delimited with the pipe character in name value pair format (e.g. - field1=-0.437).
I split the report string into the fields and then again to get each field name and numeric value.
I use StrToFloat() to convert the floating point field values in string format and assign the result of that function to a Variant variable.
This works fine on most PCs, but some of my international users are getting EConvertError's when I try to use StrToFloat() on the numeric values. Here's a concrete example of an error message from my logs:
EConvertError: '-0.685' is not a valid floating point value
As you can see -0.685 is a valid floating point number, yet I am getting the EConvertError Exception. Normally I would expect to see a comma where the decimal point is, or some other locale specific punctuation problem, but the number appears fine in this case. Also, to the best of my knowledge the external device does not even have the option to set the character set.
So what subtle nuance about Delphi 6 and international character sets might be causing this problem, perhaps related to the user's Windows XP/Win7 character settings? Note, I use standard Delphi 6 "string" cast strings throughout my program so I don't see how a multi-byte character set issue could be the root cause. Has anyone had this problem and knows what to do about it?
Your remote user's machine is expecting , for the decimal separator. When it encounters . the EConvertError exception is raised. On a machine which expects , as the decimal separator (e.g. most European and South American countries) -0.685 is indeed not a valid floating point value.
Normally I would expect to see a comma where the decimal point is, or some other locale specific punctuation problem, but the number appears fine in this case.
Your current problem is just the flip-side of the above issue. Normally, because your locale uses . as the separator, you are accustomed to seeing problems when data with , is used instead. Put yourselves in the position of somebody from a country which uses , as a separator. For them, they will be accustomed to seeing exceptions when data with . is used.
You could solve the problem by normalising the input to use the same decimal separator as the the machine locale. On a modern Delphi you could solve the problem by use the StrToFloat overload that receives a TFormatSettings parameter and explicitly specify that . is to be used as the decimal separator for this conversion. Unfortunately that facility is not available in Delphi 6.
I faced this issue for Belgian users. I also had to manually replace the '.' or ',' in the input data.
Also, if you are inserting the data into the database (sql) then, you will have to replace the ',' with '.' during insertion of the data into the database.
I was getting advice from Rob Kennedy and one of his suggestions that greatly increased the speed of an app I was working on was to use SetString and then load it into the VCL component that displayed it.
I'm using Delphi 2009 so now that PChar is Unicode,
SetString(OutputString, PChar(Output), OutputLength.Value);
edtString.Text := edtString.Text + OutputString;
Works and I changed it to PChar myself but since the data being moved isn't always Unicode in fact its usually ShortString Data.... so onto what he actually gave me to use:
SetString(OutputString, PAnsiChar(Output), OutputLength.Value);
edtString.Text := edtString.Text + OutputString;
Nothing shows up but I check in the debugger and the text that normally appeared the way I did it building 1 char at a time in the past was in the variable.
Oddly enough this is not the first time I ran into this tonight. Because I was trying to come up with another way, I took part of his advice and instead of building into a VCL's TCaption I built it into a string variable and then copied it, but when I send it over nothing's displayed. Once again in the debugger the variable that the data is built in... has the data.
for I := 0 to OutputLength.Value - 1 do
begin
OutputString := OutputString + Char(OutputData^[I]);
end;
edtString.Text := OutputString;
The above does not work but the old slow way of doing it worked just fine....
for I := 0 to OutputLength.Value - 1 do
begin
edtString.Text := edtString.Text + Char(OutputData^[I]);
end;
I tried making the variable a ShortString, String and TCaption and nothing is displayed. What I also find interesting is while I build my hex data from the same array into a richedit it's very fast while doing it inside an edit for the text data is very very slow. Which is why I haven't bothered trying to change the code for the richedit as it works superfast as it is.
Edit to add - I think I sorta found the problem but I have no solution. If I edit the value in the debugger to remove anything that can't be displayed (which by the old method used to just not display... not fail) then what I have left is displayed. So if it's just a matter of getting rid of bytes that were turned to characters that are garbage how can I fix that?
I basically have incoming raw data from a SCSI device that's being displayed hex-editor style. My original slow style of adding one char at a time successfully displayed strings and Unicode strings that did not have Unicode-specific characters in them. The faster methods even if working won't display ShortStrings one way and the other way wont display UnicodeStrings that aren't using non 0-255 characters. I really like and could use the speed boost but if it means sacrificing the ability to read the string... then what's the point in the app?
EDIT3 - Alright now that I've figured out that 0-31 is control char and 32 and up is valid I think I'm gonna make an attempt to filter char and replace those not valid with a . which is something I was planning on doing later to emulate hex editor style.
If there are any other suggestions I'd be glad to hear about them but otherwise I think I can craft a solution that's faster than the original and does what I need it to at the same time.
Some comments:
Your question is very unclear. What exactly do you want to do?
Your question reads terrible, please check your text with a spelling checker.
The question you are referring to is this one: Delphi accessing data from dynamic array that is populated from an untyped pointer
Please give a complete code sample of your function like you did in your previous question, I want to know if you implemented Rob Kennedy's suggestion or the code you gave yourself in a following answer (let's hope not :) )
As far a I understand your question: You're sending a query to your SCSI device and you get an array of bytes back which you store in the variable OutputData. After that you want to show your data to the user. So your real question is: How to show an array of bytes to the user?
Login as the same user and don't create an account for every new question. That way we can track your question history an can find out what you mean by 'getting advice'.
Some assumptions and suggestions if I'm right about the true meaning of your question:
Showing your data as a hex string won't give any problems
Showing your data in a normal Memo field gives you problems, although a Delphi string can contain any character, including 0 bytes, displaying them will give you problems. A TMemo for example will show your data till the first 0 byte. What you have to do (and you gave the answer yourself), is replacing non viewable characters with a dummy. After that you can show your data in a TMemo. Actually all hex viewers do the same, characters that cannot be printed will be shown as a dot.
I used PAnsiChar in my example for a reason. It looked like OutputLength was being measured in bytes, not characters, so I made sure to use a type whose length is always measured in bytes. You'll also notice that I showed the declaration of OutputString as an AnsiString.
Since the edit control stored Unicode, though, there will be a conversion between AnsiString and UnicodeString. That will take the system's current code page into account, but that's probably not what you want. You might want to declare the variable as a RawByteString instead. That won't have any code page associated with it, so there won't be any unexpected conversions.
Don't use strings for storing binary data. If you're building what amounts to a hex editor, then you're working with binary data. It's important to remember that. Even if your binary data happens to consist mostly of bytes that can be interpreted as text, you can't treat the data as text or you'll run into exactly the problems you're seeing — characters that don't appear as expected. If you get a bunch of bytes from your SCSI device, then store them in an array of bytes, not characters.
In hex editors, you'll notice that they always show the hexadecimal values of the bytes. They might show those bytes interpreted as characters, but that's secondary, and they generally only show the bytes that can represent ASCII characters; they don't try to get too fancy with the basic display. The good hex editors will offer to display the data interpreted as wide characters, too. This aids in debugging because the user can look at the same data in multiple ways. But they're just views of the data. They're not actually changing the binary contents of the data.
When you filter out non viewable characters...You'll probably need to decide what to do with a couple of them like #9(Tab), #10(LF), #11(Verticle Tab), #12(FF-or New Page),#13(CR)