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In exchange contract,With multi token when I call approve function from exchange contract, nor my address and spender get approved. Instead only the exchange address and spender gets approved. Its like when I call approve with spender as my contract address, in token contract it takes msg.sender as my contract address.

How to solve this issue.

With the below code, I tried calling approve function. But that's not a working properly. Kindly prefer a solution for this.

function transfer(address token, uint256 tokens)public payable // deposit perticular token balance to contract address (site address), can depoit multiple token   
{
***if(Token(token).approve(address(this),tokens))***
{
    dep_token[msg.sender][token] = safeAdd(dep_token[msg.sender][token], tokens);
    Token(token).transferFrom(msg.sender,address(this), tokens);
}
}

function token_withdraw(address token, uint256 tokens)public payable // withdraw perticular token balance from contract to user    
{
dep_token[msg.sender][token] = safeSub(dep_token[msg.sender][token] , tokens) ;   
Token(token).transfer(msg.sender, tokens);
}
1

Ask user to approve the exchange contract.

Or personally I added authorized contracts into my multiownable token contract that means that admins approve contracts that could approve to itselves to transfer anybody's tokens. And of course, I add this function into token contract. But this method is much less secure and I think many users could be afraid to use tokens with these functionality.

  • Do token contracts(multi) has to approve exchange contracts address to get placed their token in exchange site? – osiz-blockchain Mar 18 '19 at 4:53
  • Token contracts are also don't approve other contracts(and any other addresses). The token owner only can do it. But as I described my decision, it looks like admins of token contract approve exchange contracts to transfer tokens of any user. – Aleksandr Mar 18 '19 at 6:56

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