Hello World Project

Prerequisites

To get started with ICP-Client-C++ Hello World project, we recommend your development environment includes a hello world canister deployed locally. More information can be found here.

Creating the project

The complete Hello World example code can be found here.

After deploy the canister, everything is ready to start the development. A typical C++ project structure like the next one can be created, with our library being cloned inside:

── hello_world ├── CMakeLists.txt ├── icp-client-cpp └── src └── main.cpp └── inc └── rust_hello_backend.did

Since we already have the Candid file we can create the C++ header for the canister. First we compile our lib:

cd icp-client-cpp mkdir build cd build cmake .. make

Create the header file for the canister:

cd ic-agent-wrapper cargo run -p generate-cpp rust_hello_backend.did rust_hello

The rust_hello.hpp will be created inside ic-agent-wrapper/src/declarations/rust_hello/ but it can be copied to the project include folder.

Now the agent can be configured on main.cpp:

• Define canister id (info from canister deployment), candid file location and Url;

std::string id_text = "rrkah-fqaaa-aaaaa-aaaaq-cai";
std::string did_file = "../inc/rust_hello_backend.did";
std::string url = "http://127.0.0.1:4943";

• Get the candid file content to create the agent;

auto bytes_read = did_file_content(did_file, buffer);

• Create Principal and Identity;

auto principal = Principal::FromText(id_text);
Identity anonymousIdentity;

• Create agent and construct service;

auto agent = Agent::create_agent(url, std::move(anonymousIdentity),
                                std::get<Principal>(principal), buffer);
SERVICE srv(std::move(std::get<Agent>(agent)));

• Call greet method from srv;

std::string arg = "Zondax";
auto out = srv.greet(arg);

• Get the output.

  if (out.index() == 0) {
    // Print message from the canister
    std::cout << std::get<0>(out) << std::endl;
  } else {
    // Get the second string value from the variant
    std::string str2 = std::get<1>(out);
    std::cout << "Error: " << str2 << std::endl;
  }

Only compilation is missing and for that we need to edit CMakeLists.txt to link the project to the library, the file should look like this:

cmake_minimum_required(VERSION 3.15)
project(hello_world)

set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_LIBRARY_PATH "")
# OS-specific libraries
if(APPLE)
    find_library(SECURITY_LIB Security)
    find_library(COREFOUNDATION_LIB CoreFoundation)
    set(EXTRA_LIBS ${SECURITY_LIB} ${COREFOUNDATION_LIB})
elseif(UNIX AND NOT APPLE)
    set(EXTRA_LIBS m)
elseif(WIN32)
    # Add any Windows-specific libraries here
endif()

# Link against the icp-client-cpp libraries
link_directories(icp-client-cpp/build)
link_directories(icp-client-cpp/ic-agent-wrapper/target/release/)

add_executable(helloworld src/main.cpp)

# Specify libraries  to use when linking
target_link_libraries(helloworld agent_cpp agent_c ic_agent_wrapper ${EXTRA_LIBS})
# Include deirectories with .h files
target_include_directories(helloworld PRIVATE "inc")
target_include_directories(helloworld PRIVATE "icp-client-cpp/lib-agent-cpp/inc")
target_include_directories(helloworld PRIVATE "icp-client-cpp/lib-agent-c/inc")

Now everything is ready to compile and run:

mkdir build cd build cmake .. make ./helloworld

>> Hello, Zondax!