Questions about contract calling another contract

问题

Need help with two related Solidity questions.

1. Question 1. Say, I have a contract calling another one:

   contract B {
     function f1() {
        ...
     }
   }
   
   contract A {
     B b;
   
     function f() {
       b.f1();
     }
   }
   

Will msg.sender for f1 be same as for f()? Of will it be an address of a contract A?

2. Question 2. Say, I have contracts A and B. I want to have

   contract A {
     B b;
   
     A(address addr) { 
       b = B(addr); 
     }
   }
   

In other language, I would use B b = null; in declaration, to avoid double initialization, but it does not work in Solidity. So how do I declare a member variable and then initialize it by address?

回答1:

Will msg.sender for f1 be same as for f()? Of will it be an address of a contract A?

msg.sender will be the address of contract A. If you want to reference the original caller, use tx.origin.

So how do I declare a member variable and then initialize it by address?

You don't need to worry about initialization when you declare the member variable. All variables in Solidity have default values. You can follow something like this:

contract B {
    address sender;

    function B(address addr) {
        sender = addr;
    }
}

contract A {
    B b;

    function A(){
        b = B(msg.sender);
    }
}

来源：https://stackoverflow.com/questions/47858489/questions-about-contract-calling-another-contract