C++でHTTPリクエストを行うには、標準C++ライブラリだけを使って自分でコードを書くか、より高レベルのAPIを提供する外部ライブラリを使うかのどちらかだ。

以下は、純粋なC++を使ってHTTPリクエストを行う2つの例です：

```
#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <streambuf>
#include <algorithm>
#include <unordered_map>
#include <curl/curl.h>

std::string get_url(const std::string& url)
{
    CURL* curl = curl_easy_init();
    if (!curl) {
        return "";
    }

    std::stringstream ss;
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, [&](char* data, std::size_t size, std::size_t nmemb, void* userp) -> std::size_t {
        ss.write(data, size * nmemb);
        return size * nmemb;
    });
    curl_easy_perform(curl);
    curl_easy_cleanup(curl);

    return ss.str();
}

int main()
{
    std::string response = get_url("https://www.example.com");
    std::cout << response << std::endl;

    return 0;
}
And here's an example using an external library, such as libcurl:

c

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <streambuf>
#include <algorithm>
#include <unordered_map>
#include <curl/curl.h>

std::string get_url(const std::string& url)
{
    CURL* curl = curl_easy_init();
    if (!curl) {
        return "";
    }

    std::stringstream ss;
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, [&](char* data, std::size_t size, std::size_t nmemb, void* userp) -> std::size_t {
        ss.write(data, size * nmemb);
        return size * nmemb;
    });
    curl_easy_perform(curl);
    curl_easy_cleanup(curl);

    return ss.str();
}

int main()
{
    std::string response = get_url("https://www.example.com");
    std::cout << response << std::endl;

    return 0;
}
```

効率性に関しては、libcurl のような外部ライブラリを使用する方が効率的です。なぜなら、libcurl は HTTP リクエストに関わる低レベルの詳細の多くを抽象化した、より高レベルの API を提供するからです。このため、より簡潔でエラーの少ないコードを書くことが容易になり、また
To make an HTTP request in C++, you can either write the code yourself using only the standard C++ libraries, or use an external library that provides a higher-level API.

Here are two examples of making an HTTP request using pure C++:

c

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <streambuf>
#include <algorithm>
#include <unordered_map>
#include <curl/curl.h>

std::string get_url(const std::string& url)
{
    CURL* curl = curl_easy_init();
    if (!curl) {
        return "";
    }

    std::stringstream ss;
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, [&](char* data, std::size_t size, std::size_t nmemb, void* userp) -> std::size_t {
        ss.write(data, size * nmemb);
        return size * nmemb;
    });
    curl_easy_perform(curl);
    curl_easy_cleanup(curl);

    return ss.str();
}

int main()
{
    std::string response = get_url("https://www.example.com");
    std::cout << response << std::endl;

    return 0;
}
And here's an example using an external library, such as libcurl:

c

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <streambuf>
#include <algorithm>
#include <unordered_map>
#include <curl/curl.h>

std::string get_url(const std::string& url)
{
    CURL* curl = curl_easy_init();
    if (!curl) {
        return "";
    }

    std::stringstream ss;
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, [&](char* data, std::size_t size, std::size_t nmemb, void* userp) -> std::size_t {
        ss.write(data, size * nmemb);
        return size * nmemb;
    });
    curl_easy_perform(curl);
    curl_easy_cleanup(curl);

    return ss.str();
}

int main()
{
    std::string response = get_url("https://www.example.com");
    std::cout << response << std::endl;

    return 0;
}
As for efficiency, using an external library such as libcurl can be more efficient because it provides a higher-level API that abstracts away much of the low-level details involved in making an HTTP request. This makes it easier to write code that is more concise and less error-prone, and also eliminates the