Is it possible to access the current transaction ID from within a smart contract?

2 Answers 2


There are two issue on github: this which refers to this. According to these two links, you cannot access directly the transaction id, but the id is a calculated value, so you can compute it in your smart contract. From the second link, you can get this code:

void test_transaction::test_read_transaction() {
   using namespace eosio;
   checksum256 h;
   auto size = transaction_size();
   char buf[size];
   uint32_t read = read_transaction( buf, size );
   eosio_assert( size == read, "read_transaction failed");
   sha256(buf, read, &h);
   printhex( &h, sizeof(h) );

Here's an updated example using EOSIO CDT 1.6 code syntax

checksum256 get_trx_id() {
    size_t size = transaction_size();
    char buf[size];
    size_t read = read_transaction( buf, size );
    check( size == read, "read_transaction failed");
    return sha256( buf, read );

Afterwards you can include get_trx_id method into other parts of your smart contract.

table.emplace( payer, [&]( auto & row ) {
    row.trxid   = get_trx_id();
  • is this still working? I get undeclared identifier for transaction_size(), read_transaction(), and sha256(). Commented May 30, 2020 at 20:18
  • Edit: you must include eosiolib/crypto.h and eosiolib/transaction.h. However, the sha256 function header is different from the way it is used here. Commented May 30, 2020 at 20:36

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