Sending Data with POST Requests in C++

Welcome to this lesson on sending data with POST requests in C++. As you continue your exploration of interacting with RESTful APIs, you'll learn how to send data to a server using the POST method. POST requests are essential for creating new resources or submitting data, such as when filling out a web form or adding a new entry to a database. Unlike GET requests, which you have already encountered, POST requests do not solely retrieve information; they actually transmit data to an API. Understanding these differences is crucial as you expand your skill set in HTTP methods. Let’s dive deeper into utilizing POST requests to comprehend how they stand apart from GET requests.

Key Differences Between GET and POST

Before diving into POST requests, let's briefly compare them to GET requests: GET Requests : Purpose : Retrieve data from a server. Data Location : Data is sent in the URL as path or query parameters. Success Status : Expect a 200 status code for successful data retrieval. Security and Data Visibility : Data is appended to the URL, making it visible in browser history, server logs, and network tools. This makes GET unsuitable for sensitive data, such as passwords or personal information. POST Requests : Purpose : Send data to a server to create or update a resource, such as submitting a form, uploading a file, or adding a new item to a database. Data Location : Data is sent in the request body. Success Status : Expect a 201 status code for successful resource creation. Security and Data Visibility : Data is sent in the body, making it less exposed compared to GET requests, and more suitable for sensitive information. These differences clarify when to use each method. POST requests, in particular, require careful handling of the request body.

Understanding the Request Body

For POST requests, the request body is crucial as it holds the data you want to send to the server. This data is usually structured in formats like JSON, XML, or form data, with JSON being a common choice due to its readability and compatibility. Here's an example of a JSON request body using nlohmann/json : C++ #include <nlohmann/json.hpp> nlohmann::json newTodo = {{"title", "Learn C++ HTTP requests"}, {"description", "Complete a course on C++ API calls."}, {"done", false}}; #include <nlohmann/json.hpp> nlohmann::json newTodo = {{"title", "Learn C++ HTTP requests"}, {"description", "Complete a course on C++ API calls."}, {"done", false}}; This represents a new todo item, including a title, completion status, and description. Note that we are not sending an id, as this is typically managed by the server upon resource creation.

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C++

#include <nlohmann/json.hpp>

nlohmann::json newTodo = {
    {"title", "Learn C++ HTTP requests"},
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

C++

const std::string baseURL = "http://localhost:8000";

const std::string baseURL = "http://localhost:8000";

C++

// New todo data
nlohmann::json newTodo = {
    {"title", "Learn C++ HTTP requests"},
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

// New todo data
nlohmann::json newTodo = {
    {"title", "Learn C++ HTTP requests"},
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

C++

#include <httplib.h>

httplib::Client client(baseURL.c_str());
auto res = client.Post("/todos", newTodo.dump(), "application/json");

#include <httplib.h>

httplib::Client client(baseURL.c_str());
auto res = client.Post("/todos", newTodo.dump(), "application/json");

C++

if (res && res->status == 201) {
    std::cout << "New todo added successfully!" << std::endl;
    std::cout << res->body << std::endl; // The response contains the details of the newly created resource
} else {
    // Handle potential errors
    std::cerr << "Failed to add a new todo" << std::endl;
    if (res) {
        std::cerr << "Status Code: " << res->status << std::endl;
        std::cerr << "Error Details: " << res->body << std::endl;
    }
}

if (res && res->status == 201) {
    std::cout << "New todo added successfully!" << std::endl;
    std::cout << res->body << std::endl; // The response contains the details of the newly created resource
} else {
    // Handle potential errors
    std::cerr << "Failed to add a new todo" << std::endl;
    if (res) {
        std::cerr << "Status Code: " << res->status << std::endl;
        std::cerr << "Error Details: " << res->body << std::endl;
    }
}

text

New todo added successfully!
{'description': 'Complete a course on C++ API calls.', 'done': False, 'id': 5, 'title': 'Learn C++ HTTP requests'}

New todo added successfully!
{'description': 'Complete a course on C++ API calls.', 'done': False, 'id': 5, 'title': 'Learn C++ HTTP requests'}

C++

// New todo data with missing title
nlohmann::json incompleteTodo = {
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

// Send POST request
auto res = client.Post("/todos", incompleteTodo.dump(), "application/json");

// Check if the request was successful
if (res && res->status == 201) {
    std::cout << "New todo added successfully!" << std::endl;
    std::cout << res->body << std::endl;
} else {
    // Handle potential errors
    std::cerr << "Failed to add a new todo" << std::endl;
    if (res) {
        std::cerr << "Status Code: " << res->status << std::endl;
        std::cerr << "Error Details: " << res->body << std::endl;
    }
}

// New todo data with missing title
nlohmann::json incompleteTodo = {
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

// Send POST request
auto res = client.Post("/todos", incompleteTodo.dump(), "application/json");

// Check if the request was successful
if (res && res->status == 201) {
    std::cout << "New todo added successfully!" << std::endl;
    std::cout << res->body << std::endl;
} else {
    // Handle potential errors
    std::cerr << "Failed to add a new todo" << std::endl;
    if (res) {
        std::cerr << "Status Code: " << res->status << std::endl;
        std::cerr << "Error Details: " << res->body << std::endl;
    }
}

text

Failed to add a new todo
Status code: 400
Error Details: {'error': "Invalid request. 'title' is required."}

Failed to add a new todo
Status code: 400
Error Details: {'error': "Invalid request. 'title' is required."}

C++

const std::string baseURL = "http://localhost:8000";

C++

// New todo data
nlohmann::json newTodo = {
    {"title", "Learn C++ HTTP requests"},
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

C++

#include <httplib.h>

httplib::Client client(baseURL.c_str());
auto res = client.Post("/todos", newTodo.dump(), "application/json");

C++

if (res && res->status == 201) {
    std::cout << "New todo added successfully!" << std::endl;
    std::cout << res->body << std::endl; // The response contains the details of the newly created resource
} else {
    // Handle potential errors
    std::cerr << "Failed to add a new todo" << std::endl;
    if (res) {
        std::cerr << "Status Code: " << res->status << std::endl;
        std::cerr << "Error Details: " << res->body << std::endl;
    }
}

text

New todo added successfully!
{'description': 'Complete a course on C++ API calls.', 'done': False, 'id': 5, 'title': 'Learn C++ HTTP requests'}

C++

// New todo data with missing title
nlohmann::json incompleteTodo = {
    {"description", "Complete a course on C++ API calls."},
    {"done", false}
};

// Send POST request
auto res = client.Post("/todos", incompleteTodo.dump(), "application/json");

// Check if the request was successful
if (res && res->status == 201) {
    std::cout << "New todo added successfully!" << std::endl;
    std::cout << res->body << std::endl;
} else {
    // Handle potential errors
    std::cerr << "Failed to add a new todo" << std::endl;
    if (res) {
        std::cerr << "Status Code: " << res->status << std::endl;
        std::cerr << "Error Details: " << res->body << std::endl;
    }
}

text

Failed to add a new todo
Status code: 400
Error Details: {'error': "Invalid request. 'title' is required."}

Sending Data with POST Requests in C++

Key Differences Between GET and POST

Understanding the Request Body

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Utilizing a C++ HTTP Library for POST Operations

Crafting a POST Request: Adding a New Todo

Handling Responses and Error Management

Example of Unsuccessful POST Request

Summary and Overview of Practice Exercises