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 Mar 11 at 23:08









      kpopguykpopguy

      374




      374






















          2 Answers
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          2














          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



















          • 1





            "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
            Mar 12 at 1:17



















          3














          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
























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            2 Answers
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            2 Answers
            2






            active

            oldest

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            active

            oldest

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            active

            oldest

            votes









            2














            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



















            • 1





              "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
              Mar 12 at 1:17
















            2














            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



















            • 1





              "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
              Mar 12 at 1:17














            2












            2








            2







            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













            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












            share|improve this answer



            share|improve this answer










            answered Mar 12 at 1:10









            Abdullah AzizAbdullah Aziz

            3184




            3184








            • 1





              "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
              Mar 12 at 1:17














            • 1





              "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
              Mar 12 at 1:17








            1




            1





            "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
            Mar 12 at 1:17





            "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
            Mar 12 at 1:17











            3














            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




























              3














              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


























                3












                3








                3







                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 Mar 11 at 23:26









                Rob HitchensRob Hitchens

                29.5k74483




                29.5k74483






























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