How to make smart contracts accept erc20 token

Smart Contracts
1

i want my smart contract to accept erc20 token, so i used the approve function to approve some tokens to my smart contract, but when i check using the allowance function it returns zero

2

Hi, Can you share the code and test case?

3

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./IERC20.sol";

contract weth {

IERC20Permit token;

constructor(address _token) public {
   token = IERC20Permit(_token);
}

function deposit(uint _amount) public {
  token.transferFrom(msg.sender, address(this), _amount);
}

function approve(uint _amount) public returns(bool){
   return token.approve(address(this),  _amount);
}


function allow(address _owner, address _spender) public  view returns(uint){
   return token.allowance(_owner, _spender);
}

function getBalance(address _address) public view returns(uint){
  return token.balanceOf(_address);
}

}

the thing is when i call the approve function and i approve, let say 10 tokens for the contract to spend, when i call the allowance function to check its still return zero

4

first of all the user needs to call the approve function manually.
The spender is your contract.
After that your contract an initate the Transferfrom method.

5

can't the user approve through the function through the contract i created, i mean if they manually aprrove it, how do dex like uniswap work

6

No, because the token thinks that the contract wants to approve tokens to itself

7

You need to approve tokens on uniswap before trading

8

you dont understand me i have already approved some token to the contract, but i seems the approval function is not working

9

here's the approval function

10

it is working, it must be a problem from you.
can you publish your code?

11

IERC20Permit token;
constructor(address _token) public {
token = IERC20Permit(_token);
}

function deposit(uint _amount) public {
token.transferFrom(msg.sender, address(this), _amount);
}

function approve(uint _amount) public returns(bool){
return token.approve(address(this), _amount);
}

function allow(address _owner, address _spender) public view returns(uint){
return token.allowance(_owner, _spender);
}

function getBalance(address _address) public view returns(uint){
return token.balanceOf(_address);
}

12

and this me trying use transferFrom to deposit

13

function approve(uint _amount) public returns(bool){ return token.approve(address(this), _amount); }
that's the error.
what happens:
user call your contract. your contract calls token.
what should happen:
user calls token contract
The user need to approve manually

14

i understand now it's my contract that's calling token contract instead of user

15

yeah, thats right. Your user needs to call it directly