Visual Studio: Namespace not found while creating dll using cpprestsdk

Question

I want to create a dll file that can call some apis and return response (this will be used in a Unity project).

To make thing easier I installed cpprestsdk and followed this simple tutorial and it worked perfectly.

But when I tried changing my code so that I can create a dll, I started getting compilation errors.

Below is my source code -

#include <cpprest/http_client.h>
#include <cpprest/filestream.h>
#include "pch.h"

using namespace utility;                    // Common utilities like string conversions
using namespace web;                        // Common features like URIs.
using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features
using namespace concurrency::streams;       // Asynchronous streams

extern "C" {

    void SendRequest() {
        auto fileStream = std::make_shared<ostream>();

        // Open stream to output file.
        pplx::task<void> requestTask = fstream::open_ostream(U("results.html")).then([=](ostream outFile)
        {
            *fileStream = outFile;

            // Create http_client to send the request.
            http_client client(U("https://www.bing.com/"));

            // Build request URI and start the request.
            uri_builder builder(U("/search"));
            builder.append_query(U("q"), U("cpprestsdk github"));
            return client.request(methods::GET, builder.to_string());
        })

        // Handle response headers arriving.
        .then([=](http_response response)
        {
            printf("Received response status code:%u\n", response.status_code());

            // Write response body into the file.
            return response.body().read_to_end(fileStream->streambuf());
        })

    // Close the file stream.
            .then([=](size_t)
                {
                    return fileStream->close();
                });

        // Wait for all the outstanding I/O to complete and handle any exceptions
        try
        {
            requestTask.wait();
        }
        catch (const std::exception& e)
        {
            printf("Error exception:%s\n", e.what());
        }
    }

}

and my header file -

#include <cpprest/http_client.h>
#include <cpprest/filestream.h>

#define SENDREQUEST_API __declspec(dllexport) 

extern "C" {
    SENDREQUEST_API void SendRequest();
}

and the errors I am getting (truncated) -

1>C:\Users\91805\source\repos\RestAPICalls\RestAPICalls\SendRequest.cpp(5,24): error C2871: 'utility': a namespace with this name does not exist
1>C:\Users\91805\source\repos\RestAPICalls\RestAPICalls\SendRequest.cpp(6,20): error C2871: 'web': a namespace with this name does not exist
1>C:\Users\91805\source\repos\RestAPICalls\RestAPICalls\SendRequest.cpp(7,17): error C2653: 'web': is not a class or namespace name

How can I resolve above errors?

PS: I am using Visual Studio to create dll(s) and able to successfully create a dll that contains no external dependencies (followed from here)

Thanks

Answer 1

If I put all the code snippets in the header file there is no problem.

#pragma once
#include <cpprest/http_client.h>
#include <cpprest/filestream.h>
#include "pch.h"
using namespace utility;                    // Common utilities like string conversions
using namespace web;                        // Common features like URIs.
using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features
using namespace concurrency::streams;
//extern "C" {
//    SENDREQUEST_API void SendRequest();
//}
#define SENDREQUEST_API __declspec(dllexport) 

extern "C" {
    SENDREQUEST_API void SendRequest();
}

extern "C" {

    void SendRequest() {
        auto fileStream = std::make_shared<ostream>();

        // Open stream to output file.
        pplx::task<void> requestTask = fstream::open_ostream(U("results.html")).then([=](ostream outFile)
            {
                *fileStream = outFile;

                // Create http_client to send the request.
                http_client client(U("https://www.bing.com/"));

                // Build request URI and start the request.
                uri_builder builder(U("/search"));
                builder.append_query(U("q"), U("cpprestsdk github"));
                return client.request(methods::GET, builder.to_string());
            })

            // Handle response headers arriving.
                .then([=](http_response response)
                    {
                        printf("Received response status code:%u\n", response.status_code());

                        // Write response body into the file.
                        return response.body().read_to_end(fileStream->streambuf());
                    })

                // Close the file stream.
                        .then([=](size_t)
                            {
                                return fileStream->close();
                            });

                    // Wait for all the outstanding I/O to complete and handle any exceptions
                    try
                    {
                        requestTask.wait();
                    }
                    catch (const std::exception& e)
                    {
                        printf("Error exception:%s\n", e.what());
                    }
    }

}