C difference between and Equals

Question

I have a condition in a silverlight application that compares 2 strings  for some reason when I use    it returns false while  Equals   returns true   Here is the code   if    ListBoxItem lstBaseMenu SelectedItem  Content Equals  Energy Attack             Execute code    if    ListBoxItem lstBaseMenu SelectedItem  Content     Energy Attack            Execute code     Any reason as to why this is happening

User · Answer

The    operator can be used to compare two variables of any kind  and it simply compares the bits   int a   3  byte b   3  if  a    b       true     Note   there are more zeroes on the left side of the int but we don t care about that here   int a  00000011     byte b  00000011   Remember    operator cares only about the pattern of the bits in the variable   Use    If two references  primitives  refers to the same object on the heap   Rules are same whether the variable is a reference or primitive   Foo a   new Foo    Foo b   new Foo    Foo c   a   if  a    b       false   if  a    c       true   if  b    c       false     a    c is true  a    b is false  the bit pattern are the same for a and c  so they are equal using      Equal     Use the equals   method to see if two different objects are equal   Such as two different String objects that both represent the characters in  Jane

User · Answer

I am a bit confused here  If the runtime type of Content is of type string  then both    and Equals should return true  However  since this does not appear to be the case  then runtime type of Content is not string and calling Equals on it is doing a referential equality and this explains why Equals  Energy Attack   fails  However  in the second case  the decision as to which overloaded    static operator should be called is made at compile time and this decision appears to be    string string   this suggests to me that Content provides an implicit conversion to string

User · Answer

There is another dimension to an earlier answer by  BlueMonkMN   The additional dimension is that the answer to the  Drahcir s title question as it is stated also depends on how we arrived at the string value   To illustrate   string s1    test   string s2    test   string s3    test1  Substring 0  4   object s4   s3  string s5    te     st   object s6   s5  Console WriteLine   0   1   2    object ReferenceEquals s1  s2   s1    s2  s1 Equals s2     Console WriteLine   n  Case1 - A method changes the value     Console WriteLine   0   1   2    object ReferenceEquals s1  s3   s1    s3  s1 Equals s3    Console WriteLine   0   1   2    object ReferenceEquals s1  s4   s1    s4  s1 Equals s4     Console WriteLine   n  Case2 - Having only literals allows to arrive at a literal     Console WriteLine   0   1   2    object ReferenceEquals s1  s5   s1    s5  s1 Equals s5    Console WriteLine   0   1   2    object ReferenceEquals s1  s6   s1    s6  s1 Equals s6      The output is   True True True    Case1 - A method changes the value  False True True False False True    Case2 - Having only literals allows to arrive at a literal  True True True True True True

User · Answer

When we create any object there are two parts to the object one is the content and the other is reference to that content     compares both content and reference  equals   compares only content  http   www codeproject com Articles 584128 What-is-the-difference-between-equalsequals-and-Eq

User · Answer

Really great answers and examples   I would just like to add the fundamental difference between the two       Operators such as    are not polymorphic  while Equals is   With that concept in mind  if you work out any example  by looking at left hand and right hand reference type  and checking knowing if the type actually has    operator overloaded and Equals being overriden  you are certain to get the right answer

User · Answer

Just as an addition to the already good answers  This behaviour is NOT limited to Strings or comparing different numbertypes  Even if both elements are of type object of the same underlying type       won t work   The following screenshot shows the results of comparing two object  int  - values

User · Answer

When comparing an object reference to a string  even if the object reference refers to a string   the special behavior of the    operator specific to the string class is ignored  Normally  when not dealing with strings  that is   Equals compares values  while    compares object references  If two objects you are comparing are referring to the same exact instance of an object  then both will return true  but if one has the same content and came from a different source  is a separate instance with the same data   only Equals will return true  However  as noted in the comments  string is a special case because it overrides the    operator so that when dealing purely with string references  and not object references   only the values are compared even if they are separate instances  The following code illustrates the subtle differences in behaviors  string s1    quot test quot   string s2    quot test quot   string s3    quot test1 quot  Substring 0  4   object s4   s3   Console WriteLine   quot  object ReferenceEquals s1  s2    s1    s2   s1 Equals s2   quot    Console WriteLine   quot  object ReferenceEquals s1  s3    s1    s3   s1 Equals s3   quot    Console WriteLine   quot  object ReferenceEquals s1  s4    s1    s4   s1 Equals s4   quot     The output is  True True True False True True False False True

User · Answer

Adding one more point to the answer    EqualsTo   method gives you provision to compare against culture and case sensitive

User · Answer

and  Equals are both dependent upon the behavior defined in the actual type and the actual type at the call site   Both are just methods   operators which can be overridden on any type and given any behavior the author so desires   In my experience  I find it s common for people to implement  Equals on an object but neglect to implement operator      This means that  Equals will actually measure the equality of the values while    will measure whether or not they are the same reference     When I m working with a new type whose definition is in flux or writing generic algorithms  I find the best practice is the following   If I want to compare references in C   I use Object ReferenceEquals directly  not needed in the generic case  If I want to compare values I use EqualityComparer lt T gt  Default   In some cases when I feel the usage of    is ambiguous I will explicitly use Object Reference equals in the code to remove the ambiguity   Eric Lippert recently did a blog post on the subject of why there are 2 methods of equality in the CLR   It s worth the read   http   blogs msdn com ericlippert archive 2009 04 09 double-your-dispatch-double-your-fun aspx

User · Answer

The    token in C  is used for two different equality-check operators   When the compiler encounters that token  it will check whether either of the types being compared has implemented an equality-operator overload for either the specific combination types being compared     or for a combination of types to which both types can be converted   If the compiler finds such an overload it will use it   Otherwise  if the two types are both reference types and they are not unrelated classes  either may be an interface  or they may be related classes   the compiler will regard    as a reference-comparison operator   If neither condition applies  compilation will fail   Note that some other languages use separate tokens for the two equality-check operators   In VB NET  for example  the   token is used within expressions solely for the overloadable equality-check operator  and Is is used as a reference-test or null-test operator   An to use   on a type which does not override the equality-check operator will fail  as will attempting to use Is for any purpose other than testing reference equality or nullity      Types generally only overload equality for comparison with themselves  but it may be useful for types to overload the equality operator for comparison with other particular types  for example  int could have  and IMHO should have but didn t  defined an equality operators for comparison with float  so that 16777217 would not report itself equal to 16777216f   As it is  since no such operator is defined  C  will promote the int to float  rounding it to 16777216f before the equality-check operator sees it  that operator then sees two equal floating-point numbers and reports them as equal  unaware of the rounding that took place

User · Answer

The only difference between Equal and    is on object type comparison  in other cases  such as reference types and value types  they are almost the same either both are bit-wise equality or both are reference equality     object  Equals  bit-wise equality       reference equality  string   equals and    are the same for string  but if one of string changed to object  then comparison result will be different  Equals  bit-wise equality      bit-wise equality  See here for more explanation

User · Answer

Operator   If operands are Value Types and their values are equal  it returns true else false  If operands are Reference Types with exception of string and both refer to the same instance  same object   it returns true else false  If operands are string type and their values are equal  it returns true else false     Equals   If operands are Reference Types  it performs Reference Equality that is if both refer to the same instance  same object   it returns true else false  If Operands are Value Types then unlike    operator it checks for their type first and if their types are same it performs    operator else it returns false

User · Answer

Note that there are two different types of equality in C  1- Value Equality  For value types like int  DateTime and struct  2- Reference Equality  For objects  There are two basic standard protocols for implement equality checks  1- The    and    operators  2- The virtual Equals method  The    and    are statically resolve  which means C  will make a compile-time decision as to which type will perform the comparison  For instance the value-type  int x   50   int y   50   Console WriteLine  x    y      True  but for reference type  object x   50   object y   50   Console WriteLine  x    y      False   The Equals   originally resoled at runtime according to operand actual type  For instance  in the following example  at runtime  it will be decided that the Equals   will apply on int values  the result is true  object x   5  object y   5  Console WriteLine  x Equals  y       True  However  for a reference type  it will use a reference equality check  MyObject x   new MyObject    MyObject y   x  Console WriteLine  x Equals  y       True  Note that Equals   uses structural comparison for struct  which means it calls Equals on each field of a struct

User · Answer

Because the static version of the  Equal method was not mentioned so far  I would like to add this here to summarize and to compare the 3 variations  MyString Equals  quot Somestring quot               Method 1 MyString     quot Somestring quot                   Method 2 String Equals  quot Somestring quot   MyString      Method 3  static String Equals method  - better  where MyString is a variable that comes from somewhere else in the code  Background info and to summerize  In Java using    to compare strings should not be used  I mention this in case you need to use both languages and also to let you know that using    can also be replaced with something better in C   In C  there s no practical difference for comparing strings using Method 1 or Method 2 as long as both are of type string  However  if one is null  one is of another type  like an integer   or one represents an object that has a different reference  then  as the initial question shows  you may experience that comparing the content for equality may not return what you expect  Suggested solution  Because using    is not exactly the same as using  Equals when comparing things  you can use the static String Equals method instead  This way  if the two sides are not the same type you will still compare the content and  if one is null  you will avoid the exception     bool areEqual   String Equals  quot Somestring quot   MyString      It is a little more to write  but in my opinion  safer to use  Here is some info copied from Microsoft  public static bool Equals  string a  string b    Parameters a    String The first string to compare  or null  b    String The second string to compare  or null  Returns  Boolean true if the value of a is the same as the value of b  otherwise  false  If both a and b are null  the method returns true

User · Answer

Firstly  there is a difference  For numbers   gt  2    2 0 True   gt  2 Equals 2 0  False   And for strings   gt  string x   null   gt  x    null True   gt  x Equals null  NullReferenceException   In both cases     behaves more usefully than  Equals

User · Answer

When    is used on an expression of type object  it ll resolve to System Object ReferenceEquals   Equals is just a virtual method and behaves as such  so the overridden version will be used  which  for string type compares the contents

User · Answer

As far as I understand it the answer is simple       compares object references   Equals compares object content  String datatypes always act like content comparison     I hope I m correct and that it answered your question

User · Answer

I would add that if you cast your object to a string then it will work correctly  This is why the compiler will give you a warning saying      Possible unintended reference comparison  to get a value comparison    cast the left hand side to type  string

[c#] C# difference between == and Equals()

Examples related to c#

Examples related to .net

Examples related to equals