C++ CLI Engine Powered By JSON A Comprehensive Guide
In this article, we will delve into the creation of a powerful Command Line Interface (CLI) engine in C++, leveraging the versatility of JSON for configuration and data management. The goal is to build robust and flexible CLIs, such as a music player controlled via commands like player play muse or player shuffle, or a dynamic todo list application. This approach enhances modularity, maintainability, and extensibility, making it easier to manage complex applications. We will explore the benefits of using JSON, the structure of our engine, and provide practical examples to get you started.
Why JSON for CLI Applications?
When developing command-line applications, managing configurations and data efficiently is crucial. JSON (JavaScript Object Notation) stands out as an excellent choice due to its human-readable format and ease of parsing. JSON's simple structure—comprising key-value pairs and nested objects—allows for clear and organized data representation. This is particularly beneficial in CLI applications where commands and their associated parameters need to be defined and processed dynamically. Using JSON for configurations makes it easy to modify application behavior without recompiling the code, offering a high degree of flexibility and adaptability. Moreover, JSON's widespread support across programming languages and libraries simplifies integration and data exchange, making it an ideal choice for modern C++ CLI development.
Benefits of Using JSON
- Human-Readable Format: JSON's straightforward syntax ensures that configuration files are easy to read and understand. This simplifies the process of manual editing and debugging, allowing developers to quickly identify and resolve issues.
- Flexibility and Adaptability: JSON's structure allows for nested objects and arrays, making it possible to represent complex data hierarchies. This flexibility is crucial for CLI applications that require handling a variety of commands and parameters.
- Ease of Parsing: Numerous libraries are available for parsing JSON in C++, such as RapidJSON and nlohmann_json. These libraries provide efficient and easy-to-use APIs for reading and writing JSON data, streamlining development efforts.
- Dynamic Configuration: With JSON, application behavior can be modified by simply updating the configuration file. This eliminates the need to recompile the code for minor changes, making the application more adaptable to evolving requirements.
- Cross-Language Compatibility: JSON's widespread support across different programming languages and platforms makes it an excellent choice for applications that need to interact with other systems or services. This interoperability ensures seamless data exchange and integration.
Core Components of the C++ CLI Engine
To build a JSON-powered CLI engine in C++, we need to define several core components that work together seamlessly. These components include the JSON configuration parser, the command dispatcher, and the command handlers. Each component plays a crucial role in processing user input and executing the corresponding actions. A well-structured engine ensures that the application is modular, maintainable, and scalable. Let's delve into the details of each component.
1. JSON Configuration Parser
The JSON configuration parser is responsible for reading and interpreting the JSON configuration file, which defines the commands, their parameters, and the corresponding handlers. This component uses a JSON parsing library (e.g., RapidJSON or nlohmann_json) to load the JSON data into a C++ data structure, typically a nested map or a custom class hierarchy. The parser validates the configuration file against a predefined schema to ensure that it is well-formed and contains all the necessary information. Error handling is a critical aspect of this component, as malformed configurations can lead to unexpected behavior. The parsed configuration is then used to populate the command dispatcher, which we will discuss next.
2. Command Dispatcher
The command dispatcher acts as the central hub for routing commands to their respective handlers. It maintains a mapping between command names and the functions or classes that implement the command logic. When the CLI receives a user input, the dispatcher parses the command name and any associated parameters. It then looks up the corresponding handler in its mapping and invokes it with the provided parameters. The dispatcher also handles error cases, such as unknown commands or incorrect parameter usage. A well-designed dispatcher should be efficient and flexible, allowing for easy addition or modification of commands without affecting other parts of the application. This component is crucial for maintaining the modularity and scalability of the CLI engine.
3. Command Handlers
Command handlers are the individual functions or classes that implement the logic for each command. Each handler is responsible for performing a specific action, such as playing a song, adding a todo item, or displaying help information. Command handlers receive parameters from the dispatcher and use them to execute their logic. They may interact with other parts of the application, such as a music library or a database, to perform their tasks. Command handlers should be designed to be self-contained and reusable, making it easier to test and maintain the application. Proper error handling within the handlers ensures that the application behaves gracefully in unexpected situations. This component is where the core functionality of the CLI application resides, and its design directly impacts the application's usability and performance.
Setting Up the Development Environment
Before we dive into coding, it's essential to set up our development environment. This involves installing the necessary tools and libraries, as well as structuring our project in a way that promotes maintainability and scalability. We'll focus on using C++17 features and a modern build system like CMake to streamline the development process. A well-prepared environment can significantly enhance productivity and ensure a smooth development experience. Here’s a step-by-step guide to getting your environment ready.
1. Install a C++ Compiler
First, you'll need a C++ compiler that supports C++17 features. GCC (GNU Compiler Collection) and Clang are popular choices and are available on most platforms. For Windows, you can use MinGW or Visual Studio. Make sure to install the compiler and configure your system's PATH environment variable to include the compiler's binary directory. This will allow you to invoke the compiler from the command line.
2. Choose a JSON Parsing Library
Next, you'll need a JSON parsing library. As mentioned earlier, nlohmann_json and RapidJSON are excellent options. nlohmann_json is a header-only library, which means you don't need to build and link a separate library; you simply include the header file in your project. RapidJSON, on the other hand, is known for its performance and is widely used in performance-critical applications. To use nlohmann_json, download the header file from its GitHub repository and include it in your project. For RapidJSON, you'll need to clone the repository and include its headers in your project.
3. Install CMake
CMake is a cross-platform build system generator that simplifies the build process. It allows you to define your project's build configuration in a CMakeLists.txt file, and CMake will generate the appropriate build files for your chosen platform and compiler. Install CMake from the official website and ensure it's added to your system's PATH. CMake makes it easier to manage dependencies and build your project across different environments.
4. Create a Project Structure
A well-organized project structure is crucial for maintainability. Here’s a recommended structure:
my-cli-engine/
├── CMakeLists.txt
├── src/
│ ├── main.cpp
│ ├── cli_engine.h
│ ├── cli_engine.cpp
│ ├── command_handler.h
│ └── command_handler.cpp
├── include/
│ └── my-cli-engine/
│ ├── cli_engine.h
│ └── command_handler.h
└── config/
└── commands.json
CMakeLists.txt: CMake build configuration file.src/: Source files for your application.include/: Header files for your application.config/: Configuration files, such as commands.json.
5. Write a Basic CMakeLists.txt
Create a CMakeLists.txt file in the root of your project directory. Here’s a basic example:
cmake_minimum_required(VERSION 3.10)
project(MyCLIEngine)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
include_directories(include)
add_executable(my-cli-engine src/main.cpp src/cli_engine.cpp src/command_handler.cpp)
target_include_directories(my-cli-engine PUBLIC
${CMAKE_CURRENT_SOURCE_DIR}/include
)
# If using nlohmann_json, you might need to copy the header file into your include directory.
# If using RapidJSON, you might need to add it as a subdirectory and link against it.
This CMakeLists.txt file specifies the minimum CMake version, the project name, the C++ standard, include directories, and the executable target. Adjust it as needed based on your project's dependencies and structure.
6. Build the Project
To build the project, create a build directory in the root of your project, navigate into it, and run CMake:
mkdir build
cd build
cmake ..
make
This will generate the necessary build files and compile your project. The executable will be located in the build directory (or a subdirectory within it, depending on your build configuration).
Implementing the JSON Configuration Parser
At the heart of our CLI engine is the JSON configuration parser. This component is responsible for reading the JSON configuration file, parsing its contents, and making the data available to the rest of the application. We'll use a C++ JSON library, such as nlohmann_json, to handle the parsing. The parser will load the JSON data, validate its structure, and extract the necessary information to configure the CLI commands. Proper implementation of the parser is crucial for ensuring the flexibility and adaptability of our engine. Let’s explore the steps involved in building this component.
1. Choose a JSON Library
As mentioned earlier, nlohmann_json is an excellent choice due to its ease of use and header-only nature. If you haven't already, download the nlohmann_json header file from its GitHub repository and include it in your project. Alternatively, you can use RapidJSON if you prefer a library known for its performance.
2. Define the Configuration Structure
Before parsing the JSON, we need to define the structure of our configuration. Let’s assume our commands.json file looks like this:
[
{
"name": "play",
"description": "Play a song",
"handler": "play_handler",
"parameters": [
{
"name": "song",
"type": "string",
"required": true
}
]
},
{
"name": "shuffle",
"description": "Shuffle the playlist",
"handler": "shuffle_handler",
"parameters": []
}
]
This JSON structure defines an array of commands, each with a name, description, handler function, and a list of parameters. We can represent this structure in C++ using classes or structs. For simplicity, let’s use structs:
#include <string>
#include <vector>
struct Parameter {
std::string name;
std::string type;
bool required;
};
struct Command {
std::string name;
std::string description;
std::string handler;
std::vector<Parameter> parameters;
};
using CommandList = std::vector<Command>;
3. Implement the JSON Parser
Now, let’s implement the JSON parser using nlohmann_json. Create a function that takes the path to the JSON configuration file as input and returns a CommandList:
#include <fstream>
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
CommandList parse_commands_from_json(const std::string& filepath) {
CommandList commands;
std::ifstream file(filepath);
if (!file.is_open()) {
std::cerr << "Error: Could not open file " << filepath << std::endl;
return commands;
}
json j;
try {
file >> j;
} catch (const json::parse_error& e) {
std::cerr << "Error: JSON parse error: " << e.what() << std::endl;
return commands;
}
for (const auto& command_json : j) {
Command command;
command.name = command_json["name"].get<std::string>();
command.description = command_json["description"].get<std::string>();
command.handler = command_json["handler"].get<std::string>();
if (command_json.contains("parameters")) {
for (const auto& param_json : command_json["parameters"])
{
Parameter param;
param.name = param_json["name"].get<std::string>();
param.type = param_json["type"].get<std::string>();
param.required = param_json["required"].get<bool>();
command.parameters.push_back(param);
}
}
commands.push_back(command);
}
return commands;
}
This function reads the JSON file, parses it using nlohmann_json, and iterates through the array of commands. For each command, it extracts the name, description, handler, and parameters, and populates the Command struct. Error handling is included to catch file opening issues and JSON parsing errors.
4. Using the Parser
To use the parser, simply call the parse_commands_from_json function with the path to your commands.json file:
int main() {
CommandList commands = parse_commands_from_json("config/commands.json");
for (const auto& command : commands) {
std::cout << "Command: " << command.name << std::endl;
std::cout << " Description: " << command.description << std::endl;
std::cout << " Handler: " << command.handler << std::endl;
std::cout << " Parameters:" << std::endl;
for (const auto& param : command.parameters) {
std::cout << " Name: " << param.name << ", Type: " << param.type
<< ", Required: " << param.required << std::endl;
}
}
return 0;
}
This will print the parsed commands to the console, allowing you to verify that the parser is working correctly.
Building the Command Dispatcher
The command dispatcher is a crucial component of our CLI engine. It acts as a bridge between user input and the corresponding command handlers. The dispatcher receives a command from the user, identifies the appropriate handler based on the command name, and invokes the handler with the necessary parameters. A well-designed dispatcher ensures that the engine is flexible, extensible, and easy to maintain. We'll explore how to build a command dispatcher in C++, focusing on efficiency and modularity. Let's break down the steps involved in creating this essential component.
1. Define Command Handlers
Before building the dispatcher, we need to define the command handlers. These are the functions or classes that implement the logic for each command. For our example, let’s define two simple handlers for the play and shuffle commands:
#include <iostream>
#include <string>
#include <vector>
#include <map>
// Forward declaration
struct Command;
// Define a type for command handlers: function that takes a vector of strings and returns void
using CommandHandler = void (*)(const std::vector<std::string>&);
void play_handler(const std::vector<std::string>& params) {
if (params.empty()) {
std::cout << "Error: Please specify a song to play." << std::endl;
return;
}
std::cout << "Playing song: " << params[0] << std::endl;
}
void shuffle_handler(const std::vector<std::string>& params) {
std::cout << "Shuffling playlist." << std::endl;
}
These handlers take a std::vector<std::string> as input, which represents the parameters passed to the command. The play_handler expects a song name as a parameter, while the shuffle_handler takes no parameters.
2. Create a Command Map
The dispatcher needs a way to map command names to their corresponding handlers. We can use a std::map for this purpose. The map will store command names as keys and function pointers (or function objects) as values:
// Define a type for command handlers: function that takes a vector of strings and returns void
using CommandHandler = void (*)(const std::vector<std::string>&);
// Map command names to command handlers
std::map<std::string, CommandHandler> command_map;
3. Implement the Dispatcher
Now, let’s implement the dispatcher function. This function will take the command name and parameters as input, look up the handler in the command map, and invoke it:
void dispatch_command(const std::string& command_name, const std::vector<std::string>& params) {
auto it = command_map.find(command_name);
if (it != command_map.end()) {
// Command found, invoke the handler
it->second(params);
} else {
// Command not found
std::cout << "Error: Unknown command: " << command_name << std::endl;
}
}
This function uses the std::map::find method to look up the command name in the command_map. If the command is found, the corresponding handler is invoked with the provided parameters. If the command is not found, an error message is printed.
4. Populate the Command Map
We need to populate the command_map with the available commands and their handlers. This can be done at the start of the application:
int main() {
// Populate the command map
command_map["play"] = play_handler;
command_map["shuffle"] = shuffle_handler;
// Example usage
dispatch_command("play", {"song1.mp3"});
dispatch_command("shuffle", {});
dispatch_command("unknown", {});
return 0;
}
This code populates the command_map with the play and shuffle commands and their respective handlers. It then demonstrates how to use the dispatch_command function to execute commands.
5. Integrate with JSON Configuration
To make the dispatcher more dynamic, we can integrate it with the JSON configuration. Instead of hardcoding the command mappings, we can read them from the commands.json file. This allows us to add or modify commands without recompiling the code. First, we need to modify the parse_commands_from_json function to return a map of command names to handler names:
#include <map>
std::map<std::string, std::string> parse_command_handlers_from_json(const std::string& filepath) {
std::map<std::string, std::string> command_handlers;
std::ifstream file(filepath);
if (!file.is_open()) {
std::cerr << "Error: Could not open file " << filepath << std::endl;
return command_handlers;
}
json j;
try {
file >> j;
} catch (const json::parse_error& e) {
std::cerr << "Error: JSON parse error: " << e.what() << std::endl;
return command_handlers;
}
for (const auto& command_json : j) {
std::string command_name = command_json["name"].get<std::string>();
std::string handler_name = command_json["handler"].get<std::string>();
command_handlers[command_name] = handler_name;
}
return command_handlers;
}
Next, we need to modify the main function to use the parsed handler names to populate the command_map. This requires a mechanism to map handler names (strings) to actual function pointers. One way to do this is to use another map:
int main() {
// Define a map to map handler names to function pointers
std::map<std::string, CommandHandler> handler_map;
handler_map["play_handler"] = play_handler;
handler_map["shuffle_handler"] = shuffle_handler;
// Parse command handlers from JSON
auto command_handlers = parse_command_handlers_from_json("config/commands.json");
// Populate the command map using the parsed handlers
for (const auto& [command_name, handler_name] : command_handlers) {
auto it = handler_map.find(handler_name);
if (it != handler_map.end()) {
command_map[command_name] = it->second;
} else {
std::cerr << "Error: Unknown handler: " << handler_name << std::endl;
}
}
// Example usage
dispatch_command("play", {"song1.mp3"});
dispatch_command("shuffle", {});
dispatch_command("unknown", {});
return 0;
}
This approach makes the dispatcher highly flexible and configurable. New commands and handlers can be added simply by updating the commands.json file and adding the corresponding handler function to the handler_map. This modularity is crucial for building scalable and maintainable CLI applications.
Creating Command Handlers
Command handlers are the workhorses of our CLI engine. They contain the actual logic that gets executed when a command is dispatched. Each handler is responsible for performing a specific task, such as playing a song, adding a todo item, or displaying help information. The design and implementation of command handlers are critical for ensuring the functionality and usability of the CLI application. We'll discuss best practices for creating effective command handlers, including parameter validation, error handling, and interaction with other parts of the application. Let's dive into the details of building robust command handlers.
1. Define Handler Signatures
Consistency in handler signatures makes the engine more predictable and easier to use. A common approach is to define a standard handler signature that all handlers must adhere to. This typically involves taking a vector of strings as input, representing the parameters passed to the command. The handler can then parse these parameters and perform the necessary actions. Here’s an example of a standard handler signature:
// Define a type for command handlers: function that takes a vector of strings and returns void
using CommandHandler = void (*)(const std::vector<std::string>&);
This signature defines a handler as a function that takes a const std::vector<std::string>& and returns void. This allows handlers to receive an arbitrary number of string parameters, providing flexibility for different command requirements.
2. Implement Command Logic
Each command handler should implement the specific logic for the corresponding command. This might involve interacting with other parts of the application, such as a music library, a database, or the file system. The handler should perform the necessary actions and provide feedback to the user, such as printing messages to the console. For example, a play_handler might interact with a music library to start playing a song, while a todo_add_handler might add a new item to a todo list stored in a database.
Here’s an example of a play_handler that interacts with a hypothetical music library:
#include <iostream>
#include <string>
#include <vector>
// Assume we have a MusicLibrary class
class MusicLibrary {
public:
void play_song(const std::string& song) {
std::cout << "Playing song: " << song << std::endl;
// Add actual music playing logic here
}
};
MusicLibrary music_library;
void play_handler(const std::vector<std::string>& params) {
if (params.empty()) {
std::cout << "Error: Please specify a song to play." << std::endl;
return;
}
std::string song = params[0];
music_library.play_song(song);
}
3. Parameter Validation
Parameter validation is crucial for ensuring that command handlers receive the correct input. Handlers should validate the number and type of parameters before performing any actions. This helps prevent errors and ensures that the application behaves predictably. Parameter validation can involve checking the number of parameters, verifying their types (e.g., ensuring a parameter is an integer or a valid file path), and checking for required parameters.
Here’s an example of a handler with parameter validation:
#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
void volume_handler(const std::vector<std::string>& params) {
if (params.empty()) {
std::cout << "Error: Please specify a volume level." << std::endl;
return;
}
if (params.size() > 1) {
std::cout << "Error: Too many parameters." << std::endl;
return;
}
try {
int volume = std::stoi(params[0]);
if (volume < 0 || volume > 100) {
std::cout << "Error: Volume level must be between 0 and 100." << std::endl;
return;
}
std::cout << "Setting volume to: " << volume << std::endl;
// Add actual volume setting logic here
} catch (const std::invalid_argument& e) {
std::cout << "Error: Invalid volume level. Please enter a number." << std::endl;
} catch (const std::out_of_range& e) {
std::cout << "Error: Volume level out of range." << std::endl;
}
}
This volume_handler validates that exactly one parameter is provided and that it is a valid integer between 0 and 100. It also includes error handling for invalid input and out-of-range values.
4. Error Handling
Robust error handling is essential for creating reliable CLI applications. Handlers should handle potential errors gracefully and provide informative error messages to the user. This includes handling invalid input, file access errors, database connection issues, and other potential problems. Proper error handling ensures that the application doesn't crash or behave unexpectedly in the face of errors.
We’ve already seen examples of error handling in the previous examples. The play_handler checks if a song is specified, and the volume_handler includes try-catch blocks to handle exceptions thrown by std::stoi. Here’s another example that demonstrates handling file access errors:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
void save_handler(const std::vector<std::string>& params) {
if (params.empty()) {
std::cout << "Error: Please specify a filename to save to." << std::endl;
return;
}
std::string filename = params[0];
std::ofstream file(filename);
if (!file.is_open()) {
std::cout << "Error: Could not open file: " << filename << std::endl;
return;
}
file << "Data to save." << std::endl;
std::cout << "Data saved to: " << filename << std::endl;
file.close();
}
This save_handler attempts to open the specified file for writing. If the file cannot be opened, it prints an error message to the console.
5. Providing User Feedback
Providing clear and informative feedback to the user is essential for a good CLI experience. Handlers should print messages to the console to indicate the outcome of their actions. This might include success messages, error messages, or other relevant information. User feedback helps the user understand what the application is doing and how to use it effectively.
In the examples we’ve seen, handlers print messages to the console to indicate success or failure. The play_handler prints a message indicating which song is being played, the volume_handler prints the new volume level, and the save_handler prints a message indicating that the data has been saved to the file. Clear and consistent user feedback makes the CLI application more user-friendly.
Putting It All Together: A Complete Example
Now that we've covered the core components of a JSON-powered C++ CLI engine, let's put everything together and create a complete example. This will demonstrate how the parser, dispatcher, and command handlers work together to create a functional CLI application. We'll build a simple music player CLI that can play songs and shuffle the playlist. This example will serve as a starting point for building more complex CLI applications. Let’s walk through the process of integrating the components and creating a working application.
1. Define the JSON Configuration
First, let's define the JSON configuration file (commands.json) that specifies the commands and their handlers:
[
{
"name": "play",
"description": "Play a song",
"handler": "play_handler",
"parameters": [
{
"name": "song",
"type": "string",
"required": true
}
]
},
{
"name": "shuffle",
"description": "Shuffle the playlist",
"handler": "shuffle_handler",
"parameters": []
},
{
"name": "volume",
"description": "Set the volume level",
"handler": "volume_handler",
"parameters": [
{
"name": "level",
"type": "integer",
"required": true
}
]
},
{
"name": "exit",
"description": "Exit the player",
"handler": "exit_handler",
"parameters": []
}
]
This configuration defines four commands: play, shuffle, volume, and exit. Each command has a name, description, handler, and a list of parameters. The play command requires a song parameter, the volume command requires a level parameter, and the shuffle and exit commands take no parameters.
2. Implement Command Handlers
Next, let's implement the command handlers. We'll create handlers for play, shuffle, volume, and exit:
#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
// Assume we have a MusicLibrary class (you can replace this with actual music playing logic)
class MusicLibrary {
public:
void play_song(const std::string& song) {
std::cout << "Playing song: " << song << std::endl;
// Add actual music playing logic here
}
void shuffle_playlist() {
std::cout << "Shuffling playlist." << std::endl;
// Add actual shuffle logic here
}
void set_volume(int level) {
std::cout << "Setting volume to: " << level << std::endl;
// Add actual volume setting logic here
}
};
MusicLibrary music_library;
void play_handler(const std::vector<std::string>& params) {
if (params.empty()) {
std::cout << "Error: Please specify a song to play." << std::endl;
return;
}
std::string song = params[0];
music_library.play_song(song);
}
void shuffle_handler(const std::vector<std::string>& params) {
music_library.shuffle_playlist();
}
void volume_handler(const std::vector<std::string>& params) {
if (params.empty()) {
std::cout << "Error: Please specify a volume level." << std::endl;
return;
}
if (params.size() > 1) {
std::cout << "Error: Too many parameters." << std::endl;
return;
}
try {
int volume = std::stoi(params[0]);
if (volume < 0 || volume > 100) {
std::cout << "Error: Volume level must be between 0 and 100." << std::endl;
return;
}
music_library.set_volume(volume);
} catch (const std::invalid_argument& e) {
std::cout << "Error: Invalid volume level. Please enter a number." << std::endl;
} catch (const std::out_of_range& e) {
std::cout << "Error: Volume level out of range." << std::endl;
}
}
void exit_handler(const std::vector<std::string>& params) {
std::cout << "Exiting player." << std::endl;
exit(0);
}
These handlers implement the logic for playing a song, shuffling the playlist, setting the volume, and exiting the player. The MusicLibrary class is a placeholder for actual music playing logic.
3. Implement the JSON Parser
We'll use the JSON parser implementation from the previous section to parse the commands.json file. Here’s the code again for reference:
#include <fstream>
#include <iostream>
#include <nlohmann/json.hpp>
#include <string>
#include <vector>
#include <map>
using json = nlohmann::json;
struct Parameter {
std::string name;
std::string type;
bool required;
};
struct Command {
std::string name;
std::string description;
std::string handler;
std::vector<Parameter> parameters;
};
using CommandList = std::vector<Command>;
CommandList parse_commands_from_json(const std::string& filepath) {
CommandList commands;
std::ifstream file(filepath);
if (!file.is_open()) {
std::cerr << "Error: Could not open file " << filepath << std::endl;
return commands;
}
json j;
try {
file >> j;
} catch (const json::parse_error& e) {
std::cerr << "Error: JSON parse error: " << e.what() << std::endl;
return commands;
}
for (const auto& command_json : j) {
Command command;
command.name = command_json["name"].get<std::string>();
command.description = command_json["description"].get<std::string>();
command.handler = command_json["handler"].get<std::string>();
if (command_json.contains("parameters")) {
for (const auto& param_json : command_json["parameters"])
{
Parameter param;
param.name = param_json["name"].get<std::string>();
param.type = param_json["type"].get<std::string>();
param.required = param_json["required"].get<bool>();
command.parameters.push_back(param);
}
}
commands.push_back(command);
}
return commands;
}
std::map<std::string, std::string> parse_command_handlers_from_json(const std::string& filepath) {
std::map<std::string, std::string> command_handlers;
std::ifstream file(filepath);
if (!file.is_open()) {
std::cerr << "Error: Could not open file " << filepath << std::endl;
return command_handlers;
}
json j;
try {
file >> j;
} catch (const json::parse_error& e) {
std::cerr << "Error: JSON parse error: " << e.what() << std::endl;
return command_handlers;
}
for (const auto& command_json : j) {
std::string command_name = command_json["name"].get<std::string>();
std::string handler_name = command_json["handler"].get<std::string>();
command_handlers[command_name] = handler_name;
}
return command_handlers;
}
4. Implement the Command Dispatcher
We'll also use the command dispatcher implementation from the previous section:
// Define a type for command handlers: function that takes a vector of strings and returns void
using CommandHandler = void (*)(const std::vector<std::string>&);
// Map command names to command handlers
std::map<std::string, CommandHandler> command_map;
void dispatch_command(const std::string& command_name, const std::vector<std::string>& params) {
auto it = command_map.find(command_name);
if (it != command_map.end()) {
// Command found, invoke the handler
it->second(params);
} else {
// Command not found
std::cout << "Error: Unknown command: 