I had created a token using eth based blockchain via remix.ethereum.org But I need to verify the source code ,but I am not having the backup copy of source code How can I see the source code of the token . Please let me know
You cannot retrieve the original source code anymore, if no copy is available. The only way is to decompile the EVM bytecode to get a source code that is equivalent, but not equal to your original source code (it will look different but do the same).
When you compile your Solidity code to EVM bytecode, the constructor is still included. After the contract has been deployed, the constructor is discarded. Hence no constructor will be included in your decompiled code, if you only decompile the deployed bytecode of the contract. If you want to retrieve the constructor as well, you have inspect your deployment transaction, which additionally contains the constructor.