GXChain Docs

# Troubles

In the process of development, you may encounter a variety of errors, so this tutorial will be long-term inclusion of various problems (including common problems in contract and C++ related issues).

# 1.wrong about VsCode head file

The cause of the error: The source code failed to compile, causing the contract dependent header file not to be added to the environment variable.

Solution: Can be manually set in the vscode software, edit .vscode directory --> c_cpp_properties.json file

"includePath": [
    "${workspaceFolder}/**",
    "/Users/zhaoxiangfei/code/gxb-core/contracts",  //Replace with your own contract header file path
    "/Users/zhaoxiangfei/code/gxb-core/externals/magic_get/include" //Replace with your own path
],

# 2. The generated abi file is not complete

Probably because there is no comment added to the action or table called externally, causing the gxx tool to scan for abi file missing. (abi file resolution click herekhere)

Solution: Add comments to action and table, examples are as follows:

// Action without attached assets
// @abi action
void hi(std::string user){
	...
}

// Action with attached assets
// @abi action
// @abi payable
void issue(std::string pubkey, uint64_t number){
	...
}

// multi-index table
//@abi table packet i64
struct packet {
    ...
};

# 3. Failed to operate multi-index table (increase, change)

The cause of the error: The argument to the passed lambda expression is not the reference to the object, resulting in just a copy of the object being modified.

Solution: Modify the parameters of the lambda expression to a reference to the object.

offers.emplace(0, [&](auto &o) {
    o.id = offers.available_primary_key();;
    ...
});

# 4. Error about calling an action in the contract

The cause of the error: The logical reason of the action itself or the error in the abi file and the error of GRAPHENE_ABI.

Solution: Check whether abi contains the action and whether the GRAPHENE_ABI macro contains the action.

// If you do not include an action, the contract can still be deployed successfully, but the contract will not be able to process the called action when called.
GRAPHENE_ABI(hello,(hi))

# 5. Compile with gxx tool, "head file not found"

The cause of the error: Same as question 1, because the source code was not successfully compiled or the execution of sudo make install was unsuccessful, the header file was not copied to the system-related directory.

Solution: Compile the code correctly, source compile tutorial click here (opens new window), if there is a problem with the compiled source, please submit the issue on the source github page.

# 6. Update contract causes table serialization error

Cause: Updating contract deletes or modifies the fields in the table, causing serialization errors.

Solution: Update the contract, do not modify the original table, add a new table to ensure that the field order is consistent with the serialization order.

struct packet {
    uint64_t                issuer;
    std::string             pub_key;
    contract_asset          total_amount;
    uint32_t                number;
    vector<int64_t>         subpackets;

    uint64_t primary_key() const { return issuer; }

     //The serialization order needs to be consistent with the order in which the fields are defined
    GRAPHENE_SERIALIZE(packet, (issuer)(pub_key)(total_amount)(number)(subpackets))
};

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