This isn't really an issue, however I am curious. When I save a string in lets say an DataRow, it is cast to Object. When I want to use it, I have to cast it ToString. As far as I know there are several ways of doing this, first is
string name = (string)DataRowObject["name"]; //valid since I know it's a string
and another one is:
string name = DataRowObject["name"].ToString();
I am interested in what is the difference between both? Is the first more efficient? (This is just a speculation, in my head ToString() method is implemented by some looping mechanism where just casting it "could" be faster, however this is just a "gut feeling" I have).
Is there even a faster / more elegant way of doing this?
Can anyone clear this up for me?
The two are intended for different
purposes. The ToString method of any
object is supposed to return a string
representation of that object. Casting
is quite different, and the 'as' key
word performs a conditional cast, as
has been said. The 'as' key word
basically says "get me a reference of
this type to that object if that
object is this type" while ToString
says "get me a string representation
of that object". The result may be the
same in some cases but the two should
never be considered interchangeable
because, as I said, they exist for
different purposes. If your intention
is to cast then you should always use
a cast, NOT ToString.
from http://www.codeguru.com/forum/showthread.php?t=443873
see also http://bytes.com/groups/net-c/225365-tostring-string-cast
If you know it is a String then by all means cast it to a String. Casting your object is going to be faster than calling a virtual method.
Edit: Here are the results of some benchmarking:
============ Casting vs. virtual method ============
cast 29.884 1.00
tos 33.734 1.13
I used Jon Skeet's BenchmarkHelper like this:
using System;
using BenchmarkHelper;
class Program
{
static void Main()
{
Object input = "Foo";
String output = "Foo";
var results
= TestSuite.Create("Casting vs. virtual method", input, output)
.Add(cast)
.Add(tos)
.RunTests()
.ScaleByBest(ScalingMode.VaryDuration);
results.Display(ResultColumns.NameAndDuration | ResultColumns.Score,
results.FindBest());
}
static String cast(Object o)
{
return (String)o;
}
static String tos(Object o)
{
return o.ToString();
}
}
So it appears that casting is in fact slightly faster than calling ToString().
Basically in your case it is better to leave type cast because .ToString() may hide bugs. For example, your data base schema changed and name is no longer of string type but with .ToString() your code still works. So in this case it is better to use type cast.
Here is implementation of String.ToString() - nothing special =)
public override string ToString()
{
return this;
}
Downcasting is a relatively slow operation since CLR has to perform various runtime type-checks. However, in this particular scenario casting to string is more appropriate than calling ToString() for the sake of consistency (you can't call ToInt32 on object, but cast it to int) and maintanability.
I want to make one more comment
If you are going to use casting: string name = (string)DataRowObject["name"]
you will get an Exception: Unable to cast object of type 'System.DBNull' to type'System.String' in case if the record in the database table has null value.
In this scenario you have to use: string name = DataRowObject["name"].ToString() or
You have to check for null value like
if(!string.IsNullOrEmpty(DataRowObject["name"].ToString()))
{
string name = (string)DataRowObject["name"];
}
else
{
//i.e Write error to the log file
string error = "The database table has a null value";
}
For data object, I suggest you to use "as" keyword like the following code.
string name = DataRowObject["name"] as string;
Please check it before you use value.
if(name != null)
{
// statement for empty string or it has value
}
else
{
// statement for no data in this object.
}
In this case:
string name = DataRowObject["name"].ToString();
since it is a string, I think that the ToString() method of a string object is simple as:
return this;
so IMHO there is no performance penalty.
PS
I'm a Java programmer, so this anwser is only a guess.
ToString() does not perform a cast by default. Its purpose is to return a string that represents the type (e.g. "System.Object").
If you want to avoid casting you could try to think of an implementation that is strongly typed (using generics, for example) and avoids DataRowObject altogether.
I know you mentioned that the Object is a string, but incase you're afraid that the returned object is null, you can also cast using "Convert.ToString(DataRowObject["name"]);" This has the added benefit of returning an empty string (string.empty) if the object is null, to avoid any null reference exceptions (unless of course you want an exception thrown in such cases).
Related
I was looking at the following question, comparing casting to converting, which basically stated (Through all the answers), that if you know your object is a string, use (string) rather than .ToString().
That got me thinking - what if your object might be a string or int? Or does knowing its a string also extend to integers?
Would this rule apply to a byte too? (Accidently used bit earlier)
Edit
This answer shows many ways of converting an integer to a string, but that still doesn't explain which to really use.
Specifically, casting a number to a string presents no real issue, as any number can be expressed as a string (Important: not every string, however, can be expressed as an number! e.g. how would you express "banana" as a number?)
string mystring = mynumber.ToString();
works everytime, without fail (assuming non-null values in case you're using nullable types).
The same exact method applies for any primitive type, and some others (DateTime, StringBuilder, ...)
It's the conversion from string to number that can be problematic. Usually not the other way around.
Edit if you want to take advantage of direct (string) casting in case your starting object is already a string, maybe this can help?
string mystring = (myobject as string) ?? myobject.ToString();
myobject as string will try to directly cast the object to a string. If it fails, that returns null.
?? myobject.ToString() then makes sure that, in case the previous attempts resulted in null, the regular .ToString() method is called as a fallback scenario.
If you have an object which is of type int but is boxed as an object, you cast it back:
object myBoxedStr = "stringvalue";
string unboxedStr = (string)myBoxedStr;
http://msdn.microsoft.com/en-us/library/yz2be5wk.aspx
If you have a string which contains an int value, you parse (or tryparse) it
string myIntStr = "5";
int myInt = int.Parse(myIntStr);
If you don't know if the boxed type is the assummed type you use is and as
object assumedMyType = new MyType();
MyType myType = assumedMyType as MyType;
the as keyword returns null if the conversion has failed (rather than throwing an exception)
With the is keyword you can check if the assumed type is of the correct type before converting it
object assumedInt = 5;
if(assumedInt is int)
{
int myInt = (int)assumedInt;
}
The takeaway from that question is that if you know that your value is actually of the type you want, then you should cast it (e.g. (int)). This has several benefits: it is efficient, it clearly expresses your intent, and it will fail conspicuously if your presumption is false.
You use other sorts of conversions when you don't know that the value of the type you want, or when you know that it is not. For instance, if you have an array of strings, you should not use (int), but rather ParseInt and its ilk. If you have an array of objects, some of which are ints, then the as operator might be what you want.
string name = GetSql["username"].ToString();
This code running slow. Because object(object, int, double etc.) to string converting operations.
string name = (string)GetSql["username"];
This code very fast running. Because not converting operations only type designation.
int to string convert.
1-)
var number = 0;
int.TryParse("213", out number);
It is better to TryParse method because it can block error occurs.
2-)
var number = int.Parse("123");
I think that the best option, if you strongly suspect that it's a string, but not actually sure, is something like this:
string valueString = value is string ? (string) value : (value ?? string.Empty).ToString();
My experience is that best cast/convert is archived through Convert class. That's the way C# expecting from you. That class care about all that ugly things that would you normally do.
When you do type conversion or simply typecasting, it even round float to int.
i want to know typecasting in c# .net, i have below lines of code.
int i=4
object o = i // This works properly without any typecasting becausing boxing takes place automatically
string s= i // This does not work, even when the string is also reference type?
string s=(string)i //This also does not work even if i try to typecast the int to string.
string s= Convert.ToString(i); // this works.
so i want to know why string s = i and string s = (string)i does not work and whats the difference in using (string)i, i.ToString(), and Convert.ToString(i).
When it comes to boxing and unboxing, types have explicit and implicit casting. So, in some circumstances, it is easy enough for the runtime to allow for implicit conversion between two supported types, say an Int32 to a Double. However, there is no implicit or explicit conversion between an integer and a string, because obviously, a string is not an integer (despite the fact that a string can contain characters for an integer).
string s = i; // attempt at implicit cast from Int32 to String, error
object o = i; // all types inherit from Object, so you may implicitly or explicitly cast from Int32 to Object.
s = (string)i; // attempt at explicit cast from Int32 to string, error
s = i.ToString(); // conversion
s = Convert.ToString(i); // conversion
That's where Convert comes to play. Convert contains support for attempting to convert known primitives (and types supporting IConvertable) to another. So, ToString or Convert.ToString would be the preferred methods (ToString and Convert.ToString are virtually synonymous, except that ToString gives you some formatting options).
Well, string and object - both of them are reference types. However, object is a root type for all .NET types.
When you use such syntax as (string)i, you are trying to use explicit conversion beetween types. But this conversion type requires string class to know about all possible argument types.
So we have .ToString() method, which can be overriden in any class, and its return value is used as a string represenation of any object.
string s = i and string s = (string)i does not work
because I is not a string, and type CASTING is a CAST of the type, not a conversion. It only works if i contains a string or a subclass of string (which is not possible for strings, but may be for other classes).
whats the difference in using (string)i, i.ToString(), and Convert.ToString(i).
(string) i: cast i to a string, must be assignable.
i.ToString(): calls the ToSstring method, which is defiend on System.object, thus available on ALL classes and structs - but returns no sensible content if not overwritten.
Convert.ToString(i): coonverts i to a string. THis includes calling a converter which likely just calls ToString on this rare case.
At the end, casting is not aconversion. for (string) i to work i HAS TO BE A STRING, while convert tries to MAKE it a string.
You can specify implicit and explicit conversions in .net, the reason that string s = i fails is that there is no built in cast operation for an integer to a string.
see this MSDN article on casting for further information
string s= i does not work because the types don't match, int won't go into a string.
string s=(string)i does not work because it cannot asume which type conversion is to be used (i.e which base)
something like s = ""+i would work on the other hand as it would asume base 10 conversion.
so i want to know why string s = i and string s = (string)i does not work
The short answer is that there is no implict (first example above) nor explicit (second example above) cast from int to string defined. Slightly longer answer; when authoring the struct Int32 in C# no casting behaviour was programmed to enable the developer to automagically cast from an int to a string
whats the difference in using (string)i, i.ToString(), and Convert.ToString(i)
Well, the first doesn;t work as you said, and as ive explained above. The second calls the ToString method on the struct Int32, which returns (as the name implies) a string representation of the object. It should be noted that this is a brand new string, not in any way related to the original value. The third example Convert.ToString will, under the hood, call whatever the most appropriate way to turn the parameter passed in to a string - most likely just calls the ToString method - so pretty much identical to example 2.
ToString() method is override by each referance which is vitual method in the object class. string calss override that method and provide string value out of this.
The default implementation of the ToString method returns the fully qualified name of the type of the Object, as the following example shows.
Object obj = new Object();
Console.WriteLine(obj.ToString());
// The example displays the following output:
// System.Object
this behavior is inherited by reference types that do not override the ToString method.
Typecasting in C# only works along the lines of class inheritance. Object is the root of all types in C# and therefore all values can be typecast to it.
string and int do not share the same branch of inheritance and so cannot be directly cast from one to the other.
Convert.ToString() is a method designed to convert an integer to a string - there's no typecasting going on, it's just executing a method designed to convert an integer to a string representation.
i.ToString() performs the equivalent functionality to Convert.ToString(), except that i.ToString() has overloads which allow greater flexibility on the representation of the number in string format.
One last note, exceptions to the typecasting rules can be included by the developer by using a public static explicit operator method which permits the developer to convert one value to another as they see fit.
First thing to note is that every class derives from object.
Casting int to object is using an Int32.
Casting string to object is using a String.
There is no implicit cast from an integer to a string because they are in different parts of the class hierarchy - one does not in any way relate to another. However because string is used so often for output object (and therefore all its children) have a ToString() method for convenience.
However Convert is written specifically to be able to convert from one type to another, for example Convert.ToBool(x) can parse "true" or "false" to boolean, and as you have shown it can convert an integer to a string - again this is really a convenience that probably just calls Int32.ToString() under the hood.
whats the difference in the two string methods below?
string str1 = dr["RAGStatusCID"].ToString();
string str2 = (string)dr["Description"];
This will depend on what dr is. The first invokes the ToString method that each object could override on the indexer of the dr["RAGStatusCID"]. The second casts the dr["Description"] variable to a string.
If we use our telepathic skills and suppose that dr is a SqlDataReader then the two expression do pretty much the same thing except that the cast might throw an exception at runtime if the Description column is not a string.
You haven't mentioned the type of dr or what it's indexer operation returns, but ostensibly, these are two very different operations.
The first invokes the get indexer of dr and calls the ToString() method on the returned reference, allowing the object that reference refers to to provide a string representation of it's data. The generial intent of this is to allow the object itself to return a meaningful representation of itself as a string.
The second call attempts to cast the reference returned by the indexer to System.String. The object returned must either be an instance of System.String or must be a type that the compiler can invoke a custom conversion operator on. Here, the intent is to ensure that the object returned can be treated as an instance of System.String. You can read more about conversions (including user-defined ones) on MSDN.
First one calls the method that returns the string. Someone has to implement ToString method. Second one is just unboxing.
string str1 = dr["RAGStatusCID"].ToString();
This calls the .ToString() method on the object returned from the dr["RAGStatusCID"] call. It is guaranteed to return a string or null.
string str2 = (string)dr["Description"];
This attempts to cast the object returned by dr["Description"] to a string. If the object returned is not a string, then an exception is thrown.
in short, .toString() is a method, just like any other, (String) is a cast, a language construct used to treat one data type as another, compatible type.
Now for some detail:
.toString() is a method, just like any other method you may encounter. Its often thought to be a 'special' method in some way, but it isnt really, all it does is return a string. because its a member of the base Object type, it can be relied upon to be available in every object. For this reason it is generally used to provide a textual representation of the object of which it is member. By default, in c# this is the name of the type of the object. It is often desirable to override this method to provide a more meaningful name, but all it needs to do is return a string, this can be any string you like.
As noted before, theres nothing special about it, and you could just as easily have methods called ToInt(), ToDouble(), and ToChar() to provide the same functionality for there respective types.
Casting is a language construct, this means its built into the language and is implemented specifically for that language. It is used to enable compatible but different types to be used in different locations without the need for an explicit conversion.
xxx.ToString() calls a method on that object to convert it into a string object. (string)xxx assumes that the type of the object is already a string and simply performs a cast on the existing object. So in the first case a conversion happens, in the second it's just identifying the type explicitly.
To put it more succinctly, if in your example RagStatusCID is an integer and you attempted to call (string)dr["RagStatusCID"] you would get an exception because the type is not a string, it's an int. Calling .ToString() performs a conversion and the output is a string.
(string) is a casting operation. .ToString() is a method that is inherited from the Object class. Everything has a .ToString(), but not everything has a (string). Additionally certain objects will cast to a string different than the one .ToString() outputs.
I don't know if it is correct for C# but it probably is, so:
(String)myinstance calls implicitly the .toString() implementation of myinstance's class
if you have a class like this:
class User
{
private integer userId;
private integer userName;
... some code here...
public toString()
{
return "Username: " + this.userName + " (" + this.userId + ")";
}
}
with the method toString you are defining what (String)instance casting will do
User myuser = new User("Alex", 22);
String myuserdump = (String)myuser;
print(myuserdump);
will print "Username: Alex (22)"
I have a question regarding type conversion in C#.
Object data_obj = "test";
string data_str;
data_str = data_obj;
this produces an error claiming no implicit conversion exists. Now, this is, at least for me, a little bit unintuitive, since Console.WriteLine("type{0}",data_obj.GetType()) produces System.String, but then again, i am really new at C#.
Now, getting past this, i would like to cast to the type of the data stored in data_obj, without having to switch and selecting the type manually.
So, basically, what i am asking is: is there a way to define an implicit conversion from System.Object to System.String, System.Decimal, etc.
Context:
I am reading from an ODBC connection to an SQLServer database and trying to pump those rows into an Oracle Database. Now, the correspondence of SQLServer and Oracle rows have to be defined. Now, i read the data from the SQLServer table with no problem whatsoever, and i store it in a List<Dictionary<string,Object>> (i know, storing the rows seem wrong, but design requirements, what can you do).
The insertion part is where i am having problems with the insertion. I basically loop (with a foreach) through the elements of the list and insert them row by row. It is here where i need to determine the type of the data stored in the Object.
Edit: Including a bit more detail.
No, there's no way of doing it implicitly. Options:
Call ToString() explicitly (which will throw an exception if the reference is null)
Call Convert.ToString()
Use "" + data_obj (ick, don't do it)
Cast if you're sure that data_obj is really a string
Why are you so keen on an implicit conversion though?
What you should be doing in your code as noted above is casting, not converting. The object in question is a string; you simply have stored it in an object reference.
Casting would be done like so:
data_str = (string)data_obj;
The overload of Console.Writeline you are mentioning takes a format string, and then a params array of object... not strings. It calls ToString() on each of those objects. So your call to data_obj.GetType().ToString() could be slimmed down to data_obj.GetType() (calling ToString() on a string just returns the string again)
As for an implicit conversion from object to type x... think about what you are asking; a reference of object can be any CLR type. How do you handle those conversions?
You could use the Convert.ToString method:
object o = ...
string s = Convert.ToString(o);
There is no implicit conversion from object to string in C#. However you could call the object's virtual ToString method
string s = o.ToString();
If you store your value in a var instead of type object and let the compiler decide what the value is, then it can be made implicit.
var data_obj = "test";
string data_str;
data_str = data_obj;
I'm curious as to what the "right" way to convert builtin types is in .NET. Currently i use Convert.To[type]([variable]) without any null checking or anything. What is the best way to do this?
Many types have a TryParse method that you could use. For example:
string input = null;
bool result;
Boolean.TryParse(input, out result);
// result ...
The above is valid and won't throw an exception when the input to parse is null.
When it comes to converting items to a string, you can almost always rely on calling the ToString() method on the object. However, calling it on a null object will throw an exception.
StringBuilder sb = new StringBuilder();
Console.WriteLine(sb.ToString()); // valid, returns String.Empty
StringBuilder sb = null;
Console.WriteLine(sb.ToString()); // invalid, throws a NullReferenceException
One exception is calling ToString() on a nullable type, which would also return String.Empty.
int? x = null;
Console.WriteLine(x.ToString()); // no exception thrown
Thus, be careful when calling ToString; depending on the object, you may have to check for null explicitly.
See this link.
For the most part, casting says "This
object of type A is really an object
of type B-derived-from-A"
Convert.To*() functions say This
object isn't a type B, but there
exists a way to convert to type B"
Some types such as int (Int32) have a TryParse method.
If such a method exists, I try to use that.
Otherwise, I do a null check then pretty much Convert.To as you outlined.
Not sure if there is a "right" way, like most tasks it is contextual.
Kindness,
Dan
It depends on the situation. My best advice would be to study up and become familiar, so you can make better choices on your own, but you should probably start by looking into the following
System.Int32.TryParse()
(there are equivalents for most base types)
DateTime.ParseExact()