有关合同调用另一个合同的问题 [英] Questions about contract calling another contract

问题描述

需要解决两个与Solidity相关的问题。

Need help with two related Solidity questions.

1. 问题1.说，我有一份合同，其中一项要求另一个： / p>
   
   

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

contract B {
  function f1() {
     ...
  }
}

contract A {
  B b;

  function f() {
    b.f1();
  }
}

f1 的 msg.sender 与 f（）？它是合同的地址 A ？

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

1. 问题2。
   说，我有合同A和B。
   我想拥有

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

contract A {
  B b;

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

用另一种语言，我将在声明中使用 B b = null; 以避免双重初始化，但在Solidity中不起作用。那么，如何声明一个成员变量，然后按地址对其进行初始化呢？

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?

推荐答案

Will msg。 f1的发送者与f（）相同？
a合同A的地址是什么？

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

msg.sender 将是合同A的地址。如果要引用原始呼叫者，请使用 tx.origin 。

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

那么我如何声明一个成员变量，然后通过
地址初始化它？

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

声明成员变量时，您不必担心初始化。 Solidity中的所有变量均具有默认值。您可以执行以下操作：

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);
    }
}

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