gistfile1.txt

```c
typedef struct __attribute__((packed))
{
    uint32_t instruction_code; // 2 for Transfer
    
    uint64_t amount;
} util_SystemTransferData;

static uint64_t util_transfer_lamports_signed(SolPubkey *source_account, SolPubkey *destination_account,
                                              uint64_t lamports, SolSignerSeeds *seeds, int seeds_len,
                                              SolAccountInfo *transaction_accounts, int transaction_accounts_len)
{
    SolAccountMeta account_metas[] =
          ///   0. `[writable, signer]` The source account.
        { { source_account, true, true },
          ///   1. `[writable]` The destination account.
          { destination_account, true, false } };

    sol_log("util_transfer_lamports_signed");
    sol_log("source_account (writable, signer):");
    sol_log_pubkey(account_metas[0].pubkey);
    sol_log("destination_account (writable):");
    sol_log_pubkey(account_metas[1].pubkey);

    sol_log("transaction_accounts");
    for (uint32_t i = 0; i < transaction_accounts_len; i++) {
        SolAccountInfo *ta = &(transaction_accounts[i]);
        sol_log_pubkey(ta->key);
        if (ta->is_writable) {
            if (ta->is_signer) {
                sol_log("(writable, signer)");
            }
            else {
                sol_log("(writable)");
            }                
        }
        else if (ta->is_signer) {
            sol_log("(signer)");
        }
    }

    util_SystemTransferData data = { 2, lamports };

    SolInstruction instruction;

    instruction.program_id = &(Constants.system_program_id);
    instruction.accounts = account_metas;
    instruction.account_len = sizeof(account_metas) / sizeof(account_metas[0]);
    instruction.data = (uint8_t *) &data;
    instruction.data_len = sizeof(data);

    return sol_invoke_signed(&instruction, transaction_accounts, transaction_accounts_len, seeds, seeds_len);
}
```