The Ring programming language version 1.3 book - Part 83 of 88
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This document provides examples and explanations for common questions about using Ring programming language. It demonstrates how to summarize uninitialized variables, print lists containing objects, insert items into lists, print new lines and characters, create GUI applications using Qt, work with modal windows, and connect to SQLite and other databases using ODBC. Various functions, classes and concepts in Ring like Try/Catch, NULL, ISNULL(), lists, Qt classes and ODBC are explained through code examples.
![Ring Documentation, Release 1.3
Sorry, We can't use x!
Now we will talk about NULL and ISNULL()
Since we get error message when we deal with uninitialized variables
We can check these errors using Try/Catch/Done, So we uses NULL and ISNULL() for dealing with Strings.
NULL is a variable contains an empty string
ISNULL() is a function that returns true (1) if the input is an empty string or just a string contains “NULL”
This because we need to test these values (empty strings) and strings contains “NULL” that sometimes come from
external resource like DBMS.
Example
See IsNull(5) + nl + # print 0
IsNull("hello") + nl + # print 0
IsNull([1,3,5]) + nl + # print 0
IsNull("") + nl + # print 1
IsNull("NULL") # print 1
68.34 How to print lists that contains objects?
In this example we will see how we can print a list contains objects.
aList = [[1,2,3] , new point(1,2,3), new point(1,2,3)]
see "print the list" + nl
see alist
see "print the item (object)" + nl
see alist[2]
class point x y z
func init p1,p2,p3 x=p1 y=p2 z=p3
Output
print the list
1
2
3
x: 1.000000
y: 2.000000
z: 3.000000
x: 1.000000
y: 2.000000
z: 3.000000
print the item (object)
x: 1.000000
y: 2.000000
z: 3.000000
68.35 How to insert an item to the first position in the list?
To insert an item we can use the insert(aList,nIndex,Value) function.
68.34. How to print lists that contains objects? 799](https://image.slidesharecdn.com/821ringring-170615045202/85/The-Ring-programming-language-version-1-3-book-Part-83-of-88-2-320.jpg)
![Ring Documentation, Release 1.3
button = [btn1, btn2]
show()
}
exec()
}
func click
button[1] { settext ("Button3") }
button[2] { settext ("Button4") }
68.40 How to Close a window then displaying another one?
This example demonstrates how to close a window and show another one
Load "guilib.ring"
app=new qApp
{
frmBefore=new Qwidget()
{
setWindowTitle("before!")
resize(300,320)
move(200,200)
button=new qPushButton(frmBefore)
{
setText("Close")
setClickEvent("frmBefore.close() frmMain.show()")
}
show()
}
frmMain=new Qwidget()
{
setWindowTitle("After!")
resize(300,320)
move(200,200)
}
exec()
}
68.41 How to create a Modal Window?
This example demonstrates how to create a modal window
load "guilib.ring"
app=new qApp
{
68.40. How to Close a window then displaying another one? 802](https://image.slidesharecdn.com/821ringring-170615045202/85/The-Ring-programming-language-version-1-3-book-Part-83-of-88-5-320.jpg)
The Ring programming language version 1.3 book - Part 83 of 88
- 1. Ring Documentation, Release 1.3 We uses GetChar() Three times The first time we get the user option Option = GetChar() But in the second and the third times (We accept the new line characters from the buffer) GetChar() GetChar() # End of line Example : when the user select the option number 1 then press ENTER We have Three Characters • The first character is : Number 1 • The second character is : CHAR(13) • The third character is : CHAR(10) Because Windows uses CHAR(13) and CHAR(10) for each new line ( i.e. CR+LF ) 68.33 How to use NULL and ISNULL() function? when we try to use uninitialized variable in the Ring programming language, we get a clear runtime error message Example See x Output Line 1 Error (R24) : Using uninitialized variable : x in file testsseeuninit.ring The same happens when you try to access uninitialized attributes Example o1 = new point see o1 see o1.x class point x y z Output x: NULL y: NULL z: NULL Line 3 Error (R24) : Using uninitialized variable : x in file testsseeuninit2.ring if you want to check for the error, just use Try/Catch/End Try see x Catch See "Sorry, We can't use x!" + nl Done Output 68.33. How to use NULL and ISNULL() function? 798
- 2. Ring Documentation, Release 1.3 Sorry, We can't use x! Now we will talk about NULL and ISNULL() Since we get error message when we deal with uninitialized variables We can check these errors using Try/Catch/Done, So we uses NULL and ISNULL() for dealing with Strings. NULL is a variable contains an empty string ISNULL() is a function that returns true (1) if the input is an empty string or just a string contains “NULL” This because we need to test these values (empty strings) and strings contains “NULL” that sometimes come from external resource like DBMS. Example See IsNull(5) + nl + # print 0 IsNull("hello") + nl + # print 0 IsNull([1,3,5]) + nl + # print 0 IsNull("") + nl + # print 1 IsNull("NULL") # print 1 68.34 How to print lists that contains objects? In this example we will see how we can print a list contains objects. aList = [[1,2,3] , new point(1,2,3), new point(1,2,3)] see "print the list" + nl see alist see "print the item (object)" + nl see alist[2] class point x y z func init p1,p2,p3 x=p1 y=p2 z=p3 Output print the list 1 2 3 x: 1.000000 y: 2.000000 z: 3.000000 x: 1.000000 y: 2.000000 z: 3.000000 print the item (object) x: 1.000000 y: 2.000000 z: 3.000000 68.35 How to insert an item to the first position in the list? To insert an item we can use the insert(aList,nIndex,Value) function. 68.34. How to print lists that contains objects? 799
- 3. Ring Documentation, Release 1.3 aList = 1:5 insert(aList,0,0) See aList # print numbers from 0 to 5 68.36 How to print new lines and other characters? To print new line we can use the nl variable. See "Hello" + nl or we can use multi-line literal as in the next example See "Hello " if we want to print other characters we can use the char(nASCII) function See char(109) + nl + # print m char(77) # print M 68.37 Why we don’t use () after the qApp class name? When we use RingQt to create GUI application, we uses () after the class name when we create new objects for example. new qWidget() { setWindowTitle("Hello World") resize(400,400) show() } but before doing that we create an object from the qApp class and we don’t use () after that Load "guilib.ring" app = new qApp { win=new qWidget() { setwindowtitle(:test) show() } exec() } Using () after the class name means calling the init() method in the class and passing parameters to this method. If we used () while no init() method in the class we get the expected error message. The class qApp don’t have this method while the other classes have it because they need it to create an object using a function that return a pointer to that object and this pointer will be stored in an attribute called pObject, for more information see ring_qt.ring file which contains the classes. 68.38 Why the window title bar is going outside the screen? When we write the next code 68.36. How to print new lines and other characters? 800
- 4. Ring Documentation, Release 1.3 Load "guilib.ring" app = new qApp { win=new qWidget() { setwindowtitle(:test) setGeometry(0,0,200,200) show() } exec() } I would expect that the window will run at the point (0,0) with (200,200) size but the actual result is that the window title bar is going outside the screen. This is related to the behavior of Qt framework. The next code will avoid the problem load "guilib.ring" new qApp { new qWidget() { move(0,0) resize(200,200) show() } exec() } 68.39 How to create an array of buttons in GUI applications? Check the next example: Load "guilib.ring" App1 = new qApp { win1 = new qWidget() { move(0,0) resize(500,500) new qPushButton(win1) { settext("OK") setclickevent("click()") } btn1 = new qPushButton(win1) { setgeometry(100,100,100,30) settext("Button1") } btn2 = new qPushButton(win1) { setgeometry(200,100,100,30) settext("Button2") } 68.39. How to create an array of buttons in GUI applications? 801
- 5. Ring Documentation, Release 1.3 button = [btn1, btn2] show() } exec() } func click button[1] { settext ("Button3") } button[2] { settext ("Button4") } 68.40 How to Close a window then displaying another one? This example demonstrates how to close a window and show another one Load "guilib.ring" app=new qApp { frmBefore=new Qwidget() { setWindowTitle("before!") resize(300,320) move(200,200) button=new qPushButton(frmBefore) { setText("Close") setClickEvent("frmBefore.close() frmMain.show()") } show() } frmMain=new Qwidget() { setWindowTitle("After!") resize(300,320) move(200,200) } exec() } 68.41 How to create a Modal Window? This example demonstrates how to create a modal window load "guilib.ring" app=new qApp { 68.40. How to Close a window then displaying another one? 802
- 6. Ring Documentation, Release 1.3 frmStart=new Qwidget() { setWindowTitle("The First Window") resize(300,320) move(200,200) button=new qPushButton(frmStart) { setText("Show Modal Window") resize(200,30) setClickEvent("frmModal.show()") } new qPushButton(frmStart) { setText("Close Window") move(0,50) resize(200,30) setClickEvent("frmStart.Close()") } show() } frmModal =new Qwidget() { setWindowTitle("Modal Window") resize(300,320) move(200,200) setparent(frmStart) setwindowmodality(true) setwindowflags(Qt_Dialog) } exec() } Related Documents • http://doc.qt.io/qt-5/qtwidgets-widgets-windowflags-example.html • http://doc.qt.io/qt-5/qt.html#WindowType-enum • http://doc.qt.io/qt-5/qwindow.html#setParent • http://doc.qt.io/qt-5/qt.html#WindowModality-enum 68.42 How can I disable maximize button and resize window? Use the method setWindowFlags() Load "guilib.ring" app1 = new qapp { win1 = new qwidget() { setwindowtitle("First") setgeometry(100,100,500,500) 68.42. How can I disable maximize button and resize window? 803
- 7. Ring Documentation, Release 1.3 new qpushbutton(win1) { setgeometry(100,100,100,30) settext("close") setclickevent("app1.quit()") } new qpushbutton(win1) { setgeometry(250,100,100,30) settext("Second") setclickevent("second()") } showmaximized() } exec() } func second win2 = new qwidget() { setwindowtitle("Second") setgeometry(100,100,500,500) setwindowflags(Qt_dialog) show() } 68.43 How to use SQLite using ODBC? In Ring 1.1 and later versions we have native support for SQLite, so you don’t need to use it through ODBC. Also we can access SQLite through RingQt. The answer to your question pODBC = odbc_init() odbc_connect(pODBC,"DRIVER=SQLite3 ODBC Driver;Database=mydb.db;LongNames=0;"+ "Timeout=1000;NoTXN=0;SyncPragma=NORMAL;StepAPI=0;") odbc_execute(pODBC,"create table 'tel' ('ID','NAME','PHONE');") odbc_execute(pODBC,"insert into 'tel' values ('1','Mahmoud','123456');") odbc_execute(pODBC,"insert into 'tel' values ('2','Ahmed','123456');") odbc_execute(pODBC,"insert into 'tel' values ('3','Ibrahim','123456');") odbc_execute(pODBC,"select * from tel") + nl nMax = odbc_colcount(pODBC) See "Columns Count : " + nMax + nl while odbc_fetch(pODBC) See nl for x = 1 to nMax see odbc_getdata(pODBC,x) if x != nMax see " - " ok next end odbc_disconnect(pODBC) odbc_close(pODBC) Output: Columns Count : 3 68.43. How to use SQLite using ODBC? 804
- 8. Ring Documentation, Release 1.3 1 - Mahmoud - 123456 2 - Ahmed - 123456 3 - Ibrahim - 123456 The program will create the file : mydb.db Note : when I print the odbc drivers I see the long list that includes SQLite3 ODBC Driver - UsageCount=1 SQLite ODBC Driver - UsageCount=1 SQLite ODBC (UTF-8) Driver - UsageCount=1 And I’m using “SQLite3 ODBC Driver”. 68.44 Can I connect to dbase/harbour database? You can connect to any database using ODBC To connect to xbase files (*.DBF) See "Using DBF Files using ODBC" + nl pODBC = odbc_init() See "Connect to database" + nl odbc_connect(pODBC,"Driver={Microsoft dBase Driver (*.dbf)};"+ "datasource=dBase Files;DriverID=277") See "Select data" + nl odbc_execute(pODBC,"select * from tel.dbf") nMax = odbc_colcount(pODBC) See "Columns Count : " + nMax + nl while odbc_fetch(pODBC) See "Row data:" + nl for x = 1 to nMax see odbc_getdata(pODBC,x) + " - " next end See "Close database..." + nl odbc_disconnect(pODBC) odbc_close(pODBC) Output Using DBF Files using ODBC Connect to database Select data Columns Count : 3 Row data: Ahmad - Egypt - 234567 - Row data: Fady - Egypt - 345678 - Row data: Shady - Egypt - 456789 - Row data: Mahmoud - Egypt - 123456 - Close database... Also you can connect to a Visual FoxPro database (requires installing Visual FoxPro driver) See "ODBC test 6" + nl pODBC = odbc_init() See "Connect to database" + nl odbc_connect(pODBC,"Driver={Microsoft Visual FoxPro Driver};"+ "SourceType=DBC;SourceDB=C:PWCT19ssbuildPWCTDATACH1Datamydata.dbc;") 68.44. Can I connect to dbase/harbour database? 805
- 9. Ring Documentation, Release 1.3 See "Select data" + nl see odbc_execute(pODBC,"select * from t38") + nl nMax = odbc_colcount(pODBC) See "Columns Count : " + nMax + nl while odbc_fetch(pODBC) See "Row data:" + nl for x = 1 to nMax see odbc_getdata(pODBC,x) + " - " next end See "Close database..." + nl odbc_disconnect(pODBC) odbc_close(pODBC) 68.45 Why setClickEvent() doesn’t see the object methods directly? setClickEvent(cCode) take a string contains code. The code will be executed when the event happens. Ring support Many Programming Paradigms like Procedural, OOP, Functional and others. But when you support many paradigms at the language level you can’t know which paradigm will be used so you have two options 1. Provide General Solutions that works with many programming paradigms. 2. Provide Many Specific solutions where each one match a specific paradigm. setClickEvent() and others belong to (General Solutions that works with many programming paradigms). You just pass a string of code that will be executed without any care about classes and objects. This code could be anything like calling a function, calling a method and setting variable value. Some other languages force you to use OOP and call methods for events. Also some other languages uses anonymous functions that may get parameters like the current object. Now we have the general solution (not restricted with any paradigm), In the future we may add specific solutions that match specific paradigms (OOP, Functional, Declarative and Natural). 68.46 Why I get Calling Function without definition Error? Each program follow the next order 1 - Loading Files 2 - Global Variables and Statements 3 - Functions 4 - Packages, Classes and Methods So what does that mean ? 1. **** No Functions comes After Classes **** 2. **** No command is required to end functions/methods/classes/packages **** Look at this example See "Hello" test() func test see "message from the test function!" + nl class test 68.45. Why setClickEvent() doesn’t see the object methods directly? 806
- 10. Ring Documentation, Release 1.3 In the previous example we have a function called test() so we can call it directly using test() In the next example, test() will become a method See"Hello" test() # runtime error message class test func test # Test() now is a method (not a function) see "message from the test method!" + nl The errors comes when you define a method then try calling it directly as a function. The previous program must be See"Hello" new test { test() } # now will call the method class test func test # Test() now is a method (not a function) see "message from the test method!" + nl 68.47 Can Ring work on Windows XP? Ring can work on Windows XP and load extensions without problems. Just be sure that the extension can work on Windows XP and your compiler version support that (modern compilers requires some flags to support XP) Check this topic https://blogs.msdn.microsoft.com/vcblog/2012/10/08/windows-xp-targeting-with-c-in-visual-studio- 2012/ For example, We added /link /SUBSYSTEM:CONSOLE,"5.01" To the batch file to support Windows XP See : https://github.com/ring-lang/ring/blob/master/src/buildvccomplete.bat 68.48 How to extend RingQt and add more classes? You have many options In general you can extend Ring using C or C++ code Ring from Ring code you can call C Functions or use C++ Classes & Methods This chapter in the documentation explains this part in the language http://ring- lang.sourceforge.net/doc/extension.html For example the next code in .c file can be compiled to a DLL file using the Ring library (.lib) #include "ring.h" RING_FUNC(ring_ringlib_dlfunc) { printf("Message from dlfunc"); } 68.47. Can Ring work on Windows XP? 807