NFT合约标准介绍
目前，NFT（Non-Fungible Tokens）最为主流有三种合约：ERC-721、ERC-1155和ERC-998。
在NFT的最初期，大家严格遵守NFT的定义规范，也就是ERC-721规范，早年非常火热的加密猫系列就是基于该规范开发的。从 ERC-721 协议标准来看，每一个基于ERC-721创建的NFT都是独一无二、不可复制的。用户可以在智能合约中编写一段代码来创建自己的NFT，该段代码遵循一个比较基础的通用模版格式，可通过该代码添加关于NFT的所有者名称、元数据或安全文件链接等细节。
代码语言：javascript复制 *Submitted for verification at Etherscan.io on 2022-12-28
*/
pragma solidity ^0.4.17;
/**
* @title SafeMath
* @dev Math operations with safety checks that throw on error
*/
library SafeMath {
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
if (a == 0) {
return 0;
}
uint256 c = a * b;
assert(c / a == b);
return c;
}
function div(uint256 a, uint256 b) internal pure returns (uint256) {
// assert(b > 0); // Solidity automatically throws when dividing by 0
uint256 c = a / b;
// assert(a == b * c a % b); // There is no case in which this doesn't hold
return c;
}
function sub(uint256 a, uint256 b) internal pure returns (uint256) {
assert(b <= a);
return a - b;
}
function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a b;
assert(c >= a);
return c;
}
}
/**
* @title Ownable
* @dev The Ownable contract has an owner address, and provides basic authorization control
* functions, this simplifies the implementation of "user permissions".
*/
contract Ownable {
address public owner;
/**
* @dev The Ownable constructor sets the original `owner` of the contract to the sender
* account.
*/
function Ownable() public {
owner = msg.sender;
}
/**
* @dev Throws if called by any account other than the owner.
*/
modifier onlyOwner() {
require(msg.sender == owner);
_;
}
/**
* @dev Allows the current owner to transfer control of the contract to a newOwner.
* @param newOwner The address to transfer ownership to.
*/
function transferOwnership(address newOwner) public onlyOwner {
if (newOwner != address(0)) {
owner = newOwner;
}
}
