How to Call Webservice through C++ Dynamic Link Library (DLL) in Visual Studio 2019 Using C++ Rest SDK
Introduction
DLL is a one of the most useful Windows Components.
In UNIX systems known as shared libraries
DLL is used to share code and resources
It can reduce the size of your applications
Requirements
Windows 7 or Later (Windows 10 Ideal)
Check Desktop Development ith C++ Workload in the Visual Studio Installer
Create Python Flask WebService
Open Pycharm IDE
Create a project with a virtual enviornment
pip install flask
Implement a webservice (Returns a JSON response)
import flask
from flask import request, jsonify
app = flask.Flask(__name__)
app.config["DEBUG"] = True
prediction = {"prediction":
{'id': 0,
'title': 'A Fire Upon the Deep',
'author': 'Vernor Vinge',
'first_sentence': 'The coldsleep itself was dreamless.',
'year_published': '1992'
}
}
# A route to return all of the available entries in our catalog.
@app.route('/api/forex/prediction', methods=['GET'])
def api_all():
return jsonify(prediction)
@app.route('/', methods=['GET'])
def home():
return "<h1>Distant Reading Archive</h1><p>This site is a prototype API for distant reading of science fiction novels.</p>"
app.run()
Create Dynamic Link Library Project
Open Visual Studio 2019 IDE
Click Create a New Project
Select C++, Windows, Library, Select Windows Desktop Wizard
Give Project name, Solution name, Project Location
Project Name : Calculator
Click Create
Select DLL from the drop down menu
Click OK
#pragma once
#ifdef CALCULATOR_EXPORTS
#define CALCULATOR_API __declspec(dllexport)
#else
#define CALCULATOR_API __declspec(dllimport)
#endif
CALCULATOR_API int __stdcall add(int a, int b);
#include "Calculator.h"
#include <cpprest\filestream.h>
int __stdcall add(int a, int b)
{
return a + b;
}
void __stdcall saveResponse()
{
auto fileStream = std::make_shared<Concurrency::streams::ostream>();
// Open stream to output file.
pplx::task<void> requestTask = Concurrency::streams::fstream::open_ostream(U("prediction.json"))
// Make a GET request.
.then([=](Concurrency::streams::ostream outFile) {
*fileStream = outFile;
// Create http_client to send the request.
http_client client(U("http://127.0.0.1:5000"));
// Build request URI and start the request.
return client.request(methods::GET, uri_builder(U("api")).append_path(U("forex")).append_path(U("prediction")).to_string());
})
// Get the response.
.then([=](http_response response) {
// Check the status code.
if (response.status_code() != 200) {
throw std::runtime_error("Returned " + std::to_string(response.status_code()));
}
// Write the response body to file stream.
response.body().read_to_end(fileStream->streambuf()).wait();
// Close the file.
return fileStream->close();
});
// Wait for the concurrent tasks to finish.
try {
while (!requestTask.is_done()) { std::cout << "."; }
}
catch (const std::exception& e) {
printf("Error exception:%s\n", e.what());
}
}
Copy cpprestsdk (built for X64) in the same Folder which this Calculator Project exists
Right click on the project & Select Properties
C/C++ -> General
Set Additional Include Directories
..\..\cpprestsdk\Release\include
Place cpprest142_2_10d.lib in the project Directory
Linker -> Input
Set Additional Dependencies
$(ProjectDir)cpprest142_2_10d.lib
Right Click on the calculator DLL project & Build
Calculator.dll is created on the Calculator\x64\Debug\ folder
Create Client Console Project to use the DLL (DLL uses cpprestsdk)
Open Visual Studio 2019 IDE
Click Create a New Project
Select C++, Windows, Library, Select Console App
Give Project name, Solution name, Project Location
Project Name : CalculatorClient
Click Create
#include <iostream>
#include "Calculator.h"
int main()
{
int result= add(5, 5);
cout << result << endl;
saveResponse();
std::cin;
}
Right click on the project & Select Properties
C/C++ -> General
Set Additional Include Directories - Set relevant header file folders (dll headers, cpprestsdk headers)
..\..\Calculator\Calculator
..\..\cpprestsdk\Release\include
Linker -> Input
Copy cpprest142_2_10d.dll to the CalculatorClient\x64\Debug folder
Build Event - > Post-Build Event
Command Line
xcopy /y /d "..\..\Calculator\$(IntDir)Calculator.dll" "$(OutDir)"
Run the WebService
Right Click on CalculatorClient Project , Click Build (Build is a must , because only after the build it copies the dll from DLL library project)
Right Click on CalculatorClient Project , Click Debug
Projects Source Code
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