we can use both the method while passing parameters to sql query ?
then wht is the difference between them?
The MSDN article on AddWithValue() explains the difference between the 2. Within is the explaination on the subtle differences.
AddWithValue replaces the SqlParameterCollection.Add method that takes a String and an Object.
The overload of Add that takes a string and an object was deprecated because of possible ambiguity with the SqlParameterCollection.Add overload that takes a String and a SqlDbType enumeration value where passing an integer with the string could be interpreted as being either the parameter value or the corresponding SqlDbType value.
Use AddWithValue whenever you want to add a parameter by specifying its name and value.
Related
I m very confused with the string replacing methods of objective c.
Please tell where to use ReplaceCharacterInRange method and Where to use
stringByReplacingOccurrenceOfString Method.
These two methods differ a lot.
replaceStringWithCharactersInRange: withString:replaces all characters in the given range with the new string. It works on a NSMutableString and changes the string object you call it on.
In contrast stringByReplacingOccurrencesOfString:withString: replaces all occurrences of a given string, but returns a new string object. So it does work with immutable string as well.
So you use the first method if you want to keep your string but change parts of it while you use the second when you want to replace certain substrings within the string without changing the original string.
I am using a procedure which involves parameter passing and the parameter being passed is a variable. Because I have explicitly declared the data type of another parameter, I need to do the same for this one. What data type do I declare the parameter as if it is a variable?
Thanks
An example of what you are doing and what Types you are dealing with would have been nice. You can implement Overloading to provide for different parameter Types:
Friend Function FooBar(n As Integer) As Integer
Friend Function FooBar(n As Int64) As Integer
Friend Function FooBar(n As Short) As Integer
The compiler will pick the function which matches the data type being passed. Internally, they might do whatever based on the Type passed, then call another procedure to perform any stuff common to them all.
There is probably a finite number of types you need it to work with. For instance Font, Point and Rectangle probably make no sense. Even Date is dubious because you cannot do stuff to a date in the same way as with an Int or Long. String is also not likely needed because you can always pass it as FooBar(CInt(someString)) provided it does contain a valid integer or whatever.
You can also use a generic to tell the function what you are passing:
Private Function FooBar(Of T)(parm As T) As Integer
' called as:
ziggy = FooBar(Of Int32)(n)
zoey = FooBar(Of String)(str)
This might even be Private Function FooBar(Of T)(parm As T) As T if the function return varies depending on the parameter Type passed. There are many uses for this (one of which is to avoid passing a param as Object), but as a general purpose way of passing any type you want it is not a good idea: internally you will likely have to have a big If/Else to handle the different types their own way.
Turning off Option Strict is never advisable since all sorts of unwanted type conversions can take place.
In VB.NET, you can use Object as the type but with Option Strict Off. You can pass any kind of parameter in that case.
for more information, refer : https://stackoverflow.com/a/2890023/3660930
For instance, when to use
GetterUtil.getBoolean()
and when
ParamUtil.getBoolean()?
Are both same, or is it expected to be used differently according to a parameter, a variable, etc? Can you give some examples for both?
Both are util methods to avoid Null-Pointer Exceptions.
GetterUtil internally returns the default type and does the casting too. So in case where someone has passed a null value, it will return default value of the type.
Example:
Assume you have a String value "true", and you are expecting it will always be of type boolean. So you use GetterUtil.getBoolean("true") which will internally do the casting to boolen and return the value as boolean-true. Incase someone passes rubbish characters like "tr", it will be converted to boolean-false.
As mentioned ParamUtil does the same treatment with request parameters. ParamUtil internally uses the GetterUtil to have the above behaviour. It first retrieves the parameter (which always would be a string) and then passes it to GetterUtil.getType() method and in turn returns the proper type.
GetterUtil and ParmUtil both are different classes.
GetterUtil is to get the default values for basic Java data types.
ParamUtil is to retrive the values(of primitive data types) from the HttpReqeust.
Check the source code here for these two classes here
For GetterUtil
http://docs.liferay.com/portal/6.0/javadocs/src-html/com/liferay/portal/kernel/util/GetterUtil.html
For ParamUtil
http://docs.liferay.com/portal/5.1/javadocs/portal-kernel/com/liferay/portal/kernel/util/ParamUtil.java.html
I'm learning D and have seen a lot of code like this:
ushort x = to!ushort(args[1]);
I assume this casts args[1] to ushort, but what's the difference between this and cast(ushort)?
EDIT: And what other uses does the exclamation mark operator have?
In D,
to!ushort(args[1])
is shorthand for the template instantiation
to!(ushort)(args[1])
and is similar to
to<ushort>(args[1])
in languages like C++/Java/C#.
The exclamation point is to note the fact that it's not a regular argument, but a template argument.
The notation does not use angle brackets because those are ridiculously difficult to parse correctly for a compiler (they make the grammar very context-sensitive), which makes it that much more difficult to implement a correct compiler. See here for more info.
The only other use I know about is just the unary 'not' operation (e.g. false == !true)... I can't think of any other uses at the moment.
Regarding the cast:
cast(ushort) is an unchecked cast, so it won't throw an exception if the value is out of range.
to!ushort() is a checked cast, so it throws an exception if the value is out of range.
The exclamation mark here is not an operator, it is just a token part of the explicit template instantiation syntax (described in detail here).
std.conv.to (docs) is a function template for converting between arbitrary types. It is implemented entirely in the library and has no special support in the language. It has a broader and different scope compared to the cast operator.
The to template takes two type parameters; a "to" type and a "from" type, in that order. In your example, the template is explicitly instantiated with the single type argument ushort for the "to" parameter, and a second type argument string (assuming args comes from the first parameter to main) is automatically inferred from the regular function argument passed to the function (args[1]) as the "from" parameter.
The resulting function takes a string parameter and returns a ushort parsed from that string, or throws an exception if it failed. The cast operator will not attempt this kind of high-level conversion.
Note that if there is more than one explicit template parameter, or that parameter has more than one token in it (ushort is a single keyword token), you must wrap the template parameter list in parentheses:
ushort result;
result = to!(typeof(result))(args[1]);
In this example, typeof, (, result and ) are four separate tokens and the parentheses are thus required.
To answer your last question, the ! token is also used for the unary not operator, unrelated to template instantiations:
bool yes = true;
bool no = !yes; // 'no' is false
You already got two excellent answers by jA_cOp and Merhdad. I just want answer directly to the OP question (what's the difference between this and cast(ushort)?) - The difference is that cast(ushort)args[1] will not work (you cannot cast from a string to an uint just like that), while the to!(type)(param) template knows what to do with the string and how to convert it to the primitive type.
Example: I have this Objective-C code:
+(NSString*)stringWithString:(NSString*)string;
String: is the name of the argument?
NSString* is the data type of the argument?
for the last part, string I'm not sure. It's somewhat a name too. But what's the exact term?
Here's an example from the apple docs:
+ (id)dateWithTimeInterval:(NSTimeInterval)seconds sinceDate:(NSDate *)date
seconds
The number of seconds to add to date. Use a negative argument to specify a date and time before date.
date
The date.
Obviously they're looking at the variable when referencing the arguments, not the name part in front of the datatype-brackets. I was always wondering how to name this thing correctly.
Here + shows that it is class function you can access it by the class not the object.
first (NSString*) shows it returns an string then stringWithString this is the name
and after that (NSString*)is the argument type.
and finally string is the argument which use as local parameter for the function.
Name of the function , variables and classes follow a naming convention for easy understanding about the code.