what is the meaning of 0x0? say when variable gets assigned to it, example: keccak256(number) = 0x0;












1















Is 0x0 just zero? thanks



keccak256(number) = 0x0;


Or when not used as address I mean just to denote variable?






solidity remix







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    1















    Is 0x0 just zero? thanks



    keccak256(number) = 0x0;


    Or when not used as address I mean just to denote variable?






    solidity remix







    share|improve this question

























      1












      1








      1








      Is 0x0 just zero? thanks



      keccak256(number) = 0x0;


      Or when not used as address I mean just to denote variable?






      solidity remix







      share|improve this question














      Is 0x0 just zero? thanks



      keccak256(number) = 0x0;


      Or when not used as address I mean just to denote variable?






      solidity remix




      solidity remix






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked 7 hours ago









      kpopguykpopguy

      374




      374






















          2 Answers
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          The example given wouldn't actually work because you're trying to assign 0x0 to the keccak function.



          It has the same meaning as bytes32(0). So, you can go:



          require(bytes32(0) == 0x0);


          That would be comparing equivalents. It was possible to compare address and 0x0 but the trend seems to be toward explicit type casting, so you would go address(0) with a recent compiler.



          This type of expression is often used to validate inputs, in particular, catching important values that were not passed in. This is common:



          function doSomething(bytes32 key) ... {
          
  require(key != 0x0);
          
  // carry on
          
}


          Hope it helps.






          share|improve this answer































            1














            The 0x prefix means hexadecimal and it's a way to tell programs, contracts, APIs that the input should be interpreted as a hexadecimal number (we'll shorten to hex). 0x0 is actually 0 but in hex. Usually we use 0x0 to check whether the address is not set by us and it is set to default value by the solidity which is 0x0.



            require(_addressIn != address(0))



            E.g. 0x0 in Solidity is short for 0x0000000000000000000000000000000000000000, and if we use this as some address than it does have value greater than zero. check here.



            Keccak256 computes the Ethereum-SHA-3 (Keccak-256) hash (doc) of the arguments passed into the function. So the above line of code is not correct because keccak256(number) is returning the hash value which you can store in some variable, instead you are trying to treat the output hash value as an variable and assigning the 0x0 to that.



            I hope it helps.






            share|improve this answer








            New contributor




            Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.





















            • "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

              – smarx
              5 hours ago











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            2 Answers
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            2 Answers
            2






            active

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            active

            oldest

            votes






            active

            oldest

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            2














            The example given wouldn't actually work because you're trying to assign 0x0 to the keccak function.



            It has the same meaning as bytes32(0). So, you can go:



            require(bytes32(0) == 0x0);


            That would be comparing equivalents. It was possible to compare address and 0x0 but the trend seems to be toward explicit type casting, so you would go address(0) with a recent compiler.



            This type of expression is often used to validate inputs, in particular, catching important values that were not passed in. This is common:



            function doSomething(bytes32 key) ... {
            
  require(key != 0x0);
            
  // carry on
            
}


            Hope it helps.






            share|improve this answer




























              2














              The example given wouldn't actually work because you're trying to assign 0x0 to the keccak function.



              It has the same meaning as bytes32(0). So, you can go:



              require(bytes32(0) == 0x0);


              That would be comparing equivalents. It was possible to compare address and 0x0 but the trend seems to be toward explicit type casting, so you would go address(0) with a recent compiler.



              This type of expression is often used to validate inputs, in particular, catching important values that were not passed in. This is common:



              function doSomething(bytes32 key) ... {
              
  require(key != 0x0);
              
  // carry on
              
}


              Hope it helps.






              share|improve this answer


























                2












                2








                2







                The example given wouldn't actually work because you're trying to assign 0x0 to the keccak function.



                It has the same meaning as bytes32(0). So, you can go:



                require(bytes32(0) == 0x0);


                That would be comparing equivalents. It was possible to compare address and 0x0 but the trend seems to be toward explicit type casting, so you would go address(0) with a recent compiler.



                This type of expression is often used to validate inputs, in particular, catching important values that were not passed in. This is common:



                function doSomething(bytes32 key) ... {
                
  require(key != 0x0);
                
  // carry on
                
}


                Hope it helps.






                share|improve this answer













                The example given wouldn't actually work because you're trying to assign 0x0 to the keccak function.



                It has the same meaning as bytes32(0). So, you can go:



                require(bytes32(0) == 0x0);


                That would be comparing equivalents. It was possible to compare address and 0x0 but the trend seems to be toward explicit type casting, so you would go address(0) with a recent compiler.



                This type of expression is often used to validate inputs, in particular, catching important values that were not passed in. This is common:



                function doSomething(bytes32 key) ... {
                
  require(key != 0x0);
                
  // carry on
                
}


                Hope it helps.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 7 hours ago









                Rob HitchensRob Hitchens

                28.7k74481




                28.7k74481























                    1














                    The 0x prefix means hexadecimal and it's a way to tell programs, contracts, APIs that the input should be interpreted as a hexadecimal number (we'll shorten to hex). 0x0 is actually 0 but in hex. Usually we use 0x0 to check whether the address is not set by us and it is set to default value by the solidity which is 0x0.



                    require(_addressIn != address(0))



                    E.g. 0x0 in Solidity is short for 0x0000000000000000000000000000000000000000, and if we use this as some address than it does have value greater than zero. check here.



                    Keccak256 computes the Ethereum-SHA-3 (Keccak-256) hash (doc) of the arguments passed into the function. So the above line of code is not correct because keccak256(number) is returning the hash value which you can store in some variable, instead you are trying to treat the output hash value as an variable and assigning the 0x0 to that.



                    I hope it helps.






                    share|improve this answer








                    New contributor




                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.





















                    • "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

                      – smarx
                      5 hours ago
















                    1














                    The 0x prefix means hexadecimal and it's a way to tell programs, contracts, APIs that the input should be interpreted as a hexadecimal number (we'll shorten to hex). 0x0 is actually 0 but in hex. Usually we use 0x0 to check whether the address is not set by us and it is set to default value by the solidity which is 0x0.



                    require(_addressIn != address(0))



                    E.g. 0x0 in Solidity is short for 0x0000000000000000000000000000000000000000, and if we use this as some address than it does have value greater than zero. check here.



                    Keccak256 computes the Ethereum-SHA-3 (Keccak-256) hash (doc) of the arguments passed into the function. So the above line of code is not correct because keccak256(number) is returning the hash value which you can store in some variable, instead you are trying to treat the output hash value as an variable and assigning the 0x0 to that.



                    I hope it helps.






                    share|improve this answer








                    New contributor




                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.





















                    • "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

                      – smarx
                      5 hours ago














                    1












                    1








                    1







                    The 0x prefix means hexadecimal and it's a way to tell programs, contracts, APIs that the input should be interpreted as a hexadecimal number (we'll shorten to hex). 0x0 is actually 0 but in hex. Usually we use 0x0 to check whether the address is not set by us and it is set to default value by the solidity which is 0x0.



                    require(_addressIn != address(0))



                    E.g. 0x0 in Solidity is short for 0x0000000000000000000000000000000000000000, and if we use this as some address than it does have value greater than zero. check here.



                    Keccak256 computes the Ethereum-SHA-3 (Keccak-256) hash (doc) of the arguments passed into the function. So the above line of code is not correct because keccak256(number) is returning the hash value which you can store in some variable, instead you are trying to treat the output hash value as an variable and assigning the 0x0 to that.



                    I hope it helps.






                    share|improve this answer








                    New contributor




                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.










                    The 0x prefix means hexadecimal and it's a way to tell programs, contracts, APIs that the input should be interpreted as a hexadecimal number (we'll shorten to hex). 0x0 is actually 0 but in hex. Usually we use 0x0 to check whether the address is not set by us and it is set to default value by the solidity which is 0x0.



                    require(_addressIn != address(0))



                    E.g. 0x0 in Solidity is short for 0x0000000000000000000000000000000000000000, and if we use this as some address than it does have value greater than zero. check here.



                    Keccak256 computes the Ethereum-SHA-3 (Keccak-256) hash (doc) of the arguments passed into the function. So the above line of code is not correct because keccak256(number) is returning the hash value which you can store in some variable, instead you are trying to treat the output hash value as an variable and assigning the 0x0 to that.



                    I hope it helps.







                    share|improve this answer








                    New contributor




                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.









                    share|improve this answer



                    share|improve this answer






                    New contributor




                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.









                    answered 5 hours ago









                    Abdullah AzizAbdullah Aziz

                    311




                    311




                    New contributor




                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.





                    New contributor





                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.






                    Abdullah Aziz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.













                    • "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

                      – smarx
                      5 hours ago



















                    • "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

                      – smarx
                      5 hours ago

















                    "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

                    – smarx
                    5 hours ago





                    "0x0 in Solidity is short for 0x0000000000000000000000000000000000000000" I guess technically that's true, just like in decimal, 0 is short for 0000000000 (for any number of 0s). But I think it's misleading to say that, as it makes people think it represents some special value or some specific type. It just means 0.

                    – smarx
                    5 hours ago


















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