inline transfer causes error

Question

My inline transfer causes the following error.

Error 3050003: eosio_assert_message assertion failure
Error Details:
assertion failure with message: read

I dont know how to solve it. I simplify my code in the following version

test.hpp

#ifndef TEST_HPP
#define TEST_HPP

#include <eosiolib/asset.hpp>
#include <eosiolib/eosio.hpp>

using namespace eosio;

class test: public contract {
public:
    //@abi action
    test(account_name _self): contract(_self) {}
    void func();
};
#endif

test.cpp

#include "test.hpp"

void test::func() {
    require_auth(_self);
    action(
        permission_level {_self,N(active)},
        N(eosio.token),N(transfer),
        std::make_tuple(_self,N(eosio.token),asset(10000,symbol_type(S(4,SYS))),"")
    ).send();
}

EOSIO_ABI(test,(func))

I altered permission to allow inline transferring with command

cleos --wallet-url http://localhost:8899 -u http://localhost:8788 set account permission test active '{"threshold":1,"keys":[{"key":"EOS5BL1oic5zZfzbS681xPKgBGH8cE6f3FiGAoB2gfqDpu15fyU1L","weight":1}],"accounts":[{"permission":{"actor":"test","permission":"eosio.code"},"weight":1}],"waits":[]}' owner -p test -x 10

How can I deal with the error?

Answer 1

std::make_tuple(_self,N(eosio.token),asset(10000,symbol_type(S(4,SYS))),std::string(""))

is okay.

Answer 2

This is a limitation of std::make_tuple, the type of const char* is not the same as std::string, and will package this as a pointer. The type of the memo field is an std::string, so explicit construction is needed for make_tuple to do the right thing.