Automating Web Requests with C++ Builder (REST API Integration)

C++ Builder simplifies REST API integration through built-in components that handle requests and responses efficiently. Automating web interactions is straightforward with the right tools, reducing manual processes and ensuring seamless communication between applications and web services. This guide covers the use of REST components in C++ Builder and demonstrates data retrieval from an email validation API.

Setting Up REST API Integration in C++ Builder

Required Components

C++ Builder provides several components for handling RESTful requests:

TRESTClient – Defines the base URL of the API.
TRESTRequest – Configures request parameters and executes the call.
TRESTResponse – Stores the response data.

These components work together to send and process HTTP requests.

Adding REST Components to a Project

Open C++ Builder and create a new VCL Forms Application.
Drag TRESTClient, TRESTRequest, and TRESTResponse onto the form.
Set the BaseURL property of TRESTClient to the target API’s endpoint.
Link TRESTRequest to TRESTClient and assign TRESTResponse to store results.
Configure request properties such as Method (rmGET, rmPOST, etc.) and required headers.

Fetching Data from an Email Validation API

API Selection and Configuration

For this example, an email validation API provides verification data for an email address. The API returns details like validity, domain existence, and format correctness.

Example API Endpoint:

https://api.emailvalidation.com/v1/[email protected]&apikey=your_api_key

Implementing the API Call in C++ Builder

Step 1: Setting Up Components

Set BaseURL of TRESTClient to https://api.emailvalidation.com/v1/check.
Set Resource in TRESTRequest to email={email}&apikey={apikey}.
Define Request Parameters for dynamic email input.

Step 2: Writing the API Request Code

#include <System.JSON.hpp>
#include <REST.Client.hpp>
#include <REST.Types.hpp>
#include <memory>

void __fastcall TForm1::ValidateEmailClick(TObject *Sender)
{
    std::unique_ptr<TRESTClient> RestClient(new TRESTClient("https://api.emailvalidation.com/v1/check"));
    std::unique_ptr<TRESTRequest> RestRequest(new TRESTRequest);
    std::unique_ptr<TRESTResponse> RestResponse(new TRESTResponse);

    RestClient->Accept = "application/json";
    RestRequest->Client = RestClient.get();
    RestRequest->Response = RestResponse.get();
    RestRequest->Method = rmGET;

    RestRequest->AddParameter("email", EditEmail->Text, TRESTRequestParameterKind::pkURLSEGMENT);
    RestRequest->AddParameter("apikey", "your_api_key", TRESTRequestParameterKind::pkURLSEGMENT);

    RestRequest->Execute();

    TJSONObject *jsonResponse = (TJSONObject*)TJSONObject::ParseJSONValue(RestResponse->Content);
    if (jsonResponse) {
        ShowMessage("Valid: " + jsonResponse->GetValue("is_valid")->ToString());
        delete jsonResponse;
    }
}

Step 3: Handling JSON Response

Extract values from the JSON object.
Display results using ShowMessage or update a UI component.

Parsing and Using API Data

Extracting Key Information

Most APIs return JSON-formatted responses. C++ Builder includes System.JSON.hpp to parse and manipulate JSON objects.

Example Response from Email Validation API:

{
  "email": "[email protected]",
  "is_valid": true,
  "domain_exists": true,
  "disposable": false
}

To access these values:

bool isValid = jsonResponse->GetValue("is_valid")->AsBoolean();
bool domainExists = jsonResponse->GetValue("domain_exists")->AsBoolean();
bool isDisposable = jsonResponse->GetValue("disposable")->AsBoolean();

Displaying Results in the UI

Use TLabel or TMemo to show extracted values.
Highlight invalid emails with color changes.

Handling Errors and Exceptions

Common API Errors

Invalid API Key – Ensure the correct key is used.
Rate Limit Exceeded – Some APIs enforce limits on requests per minute.
Malformed Requests – Verify query parameters are structured correctly.

Implementing Error Handling in C++ Builder

try {
    RestRequest->Execute();
    if (RestResponse->StatusCode != 200) {
        throw Exception("API request failed: " + RestResponse->StatusText);
    }
} catch (Exception &e) {
    ShowMessage("Error: " + e.Message);
}

Try-catch blocks prevent crashes.
Response status codes help identify failures.

Optimizing API Requests

Reducing API Calls

Cache responses to avoid redundant requests.
Validate user input before sending API requests.

Using Asynchronous Execution

REST components in C++ Builder allow non-blocking calls.
Avoid UI freezes by running requests in background threads.

void __fastcall TForm1::AsyncExecute(TObject *Sender)
{
    RestRequest->ExecuteAsync();
}

Temporary Email Services for Testing APIs

During development, using real email addresses isn’t always practical. Temporary mail services provide disposable addresses to test API responses without exposing actual accounts. These services ensure repeatable test cases and help verify handling of invalid or disposable emails.

Expanding REST API Integration in C++ Builder

Authenticating API Requests

Many APIs require authentication via API keys, OAuth tokens, or Basic Authentication.
C++ Builder allows headers to be added for secure requests.

RestRequest->AddAuthParameter("Authorization", "Bearer your_token", TRESTRequestParameterKind::pkHTTPHEADER);

Sending POST Requests

For APIs that require data submission, use rmPOST.
Set request body using TJSONObject.

std::unique_ptr<TJSONObject> jsonBody(new TJSONObject);
jsonBody->AddPair("email", EditEmail->Text);
RestRequest->AddBody(jsonBody->ToString(), ctAPPLICATION_JSON);
RestRequest->Method = rmPOST;

Conclusion

C++ Builder’s REST components simplify API integration by managing requests, responses, and error handling. By leveraging built-in tools, developers can automate data retrieval, process JSON responses, and create efficient applications that interact with web services effortlessly.