51Degrees Device Detection C/C++  4.4

A device detection library that is used natively or by 51Degrees products


Reload from file example of using 51Degrees device detection.This example shows how to:

  1. Only maintain a reference to a single EngineHash instance and use the reference to process data.
  2. Use the EngineHash->refreshData() function to reload the dataset from the same location and with the same set of properties.
  3. Retrieve a results instance from the engine and release it when done with detecting current User-Agent.
  4. Use the reload functionality in a single threaded environment.
  5. Use the reload functionality in a multi threaded environment.

This example illustrates how to use a single reference to the engine to use device detection and invoke the reload functionality instead of maintaining a reference to the dataset directly.

The EngineHash->refreshData() function requires an existing engine with the initialized dataset. Function reloads the dataset from the same location and with the same parameters as the original dataset.

Please keep in mind that even if the current dataset was constructed with all available properties this does not guarantee that the new dataset will be initialized with the same set of properties. If the new data file contains properties that were not part of the original data file, the new extra property(ies) will not be initialized. If the new data file does not contain one or more property that were previously available, then these property(ies) will not be initialized.

Each successful data file reload should be accompanied by the integrity check to verify that the properties you want have indeed been loaded. This can be achieved by simply comparing the number of properties before and after the reload as the number can not go up but it can go down.

The reload functionality works both with the single threaded as well as the multi threaded modes. To try the reload functionality in single threaded mode build with FIFTYONE_DEGREES_NO_THREADING defined. Or build without FIFTYONE_DEGREES_NO_THREADING for multi threaded example.

In a single threaded environment the reload function is executed as part of the normal flow of the program execution and will prevent any other actions until the reload is complete. The reload itself takes less than half a second even for Enterprise dataset. For more information see: https://51degrees.com/Support/Documentation/APIs/C-V32/Benchmarks

/* *********************************************************************
* This Original Work is copyright of 51 Degrees Mobile Experts Limited.
* Copyright 2022 51 Degrees Mobile Experts Limited, Davidson House,
* Forbury Square, Reading, Berkshire, United Kingdom RG1 3EU.
* This Original Work is licensed under the European Union Public Licence
* (EUPL) v.1.2 and is subject to its terms as set out below.
* If a copy of the EUPL was not distributed with this file, You can obtain
* one at https://opensource.org/licenses/EUPL-1.2.
* The 'Compatible Licences' set out in the Appendix to the EUPL (as may be
* amended by the European Commission) shall be deemed incompatible for
* the purposes of the Work and the provisions of the compatibility
* clause in Article 5 of the EUPL shall not apply.
* If using the Work as, or as part of, a network application, by
* including the attribution notice(s) required under Article 5 of the EUPL
* in the end user terms of the application under an appropriate heading,
* such notice(s) shall fulfill the requirements of that article.
* ********************************************************************* */
#include <string>
#include <iostream>
#include <thread>
// Include ExmapleBase.h before others as it includes Windows 'crtdbg.h'
// which requires to be included before 'malloc.h'.
#include "../../C/Hash/ExampleBase.h"
#include "../../../src/hash/EngineHash.hpp"
#include "ExampleBase.hpp"
using namespace std;
using namespace FiftyoneDegrees::Common;
namespace FiftyoneDegrees {
namespace Examples {
namespace Hash {
class ReloadFromFile : public ExampleBase {
string dataFilePath,
string userAgentFilePath,
ConfigHash *config)
: ExampleBase(dataFilePath, config) {
this->userAgentFilePath = userAgentFilePath;
void run() {
int numberOfReloads = 0;
int numberOfReloadFails = 0;
ExampleBase::SharedState state(engine, userAgentFilePath);
printf("** Multi Threaded Reload Example **\r\n");
while (state.threadsFinished < THREAD_COUNT) {
try {
#ifdef _MSC_VER
Sleep(2000); // milliseconds
usleep(20000000); // microseconds
else {
printf("** Single Threaded Reload Example **\r\n");
try {
// Report the number of reloads.
printf("Reloaded '%i' times.\r\n", numberOfReloads);
printf("Failed to reload '%i' times.\r\n", numberOfReloadFails);
printf("Program execution complete. Press Return to exit.");
string userAgentFilePath;
extern "C" void fiftyoneDegreesExampleCPPReloadFromFileRun(ExampleParameters *params) {
// Call the actual function.
ConfigHash* cppConfig = new ConfigHash(&configHash);
ReloadFromFile *reloadFromFile = new ReloadFromFile(
delete reloadFromFile;
#ifndef TEST
int main(int argc, char* argv[]) {
if (argc > 1) {
strcpy(dataFilePath, argv[1]);
else {
ExampleBase::reportStatus(status, dataFileName);
return 1;
if (argc > 2) {
strcpy(dataFilePath, argv[2]);
else {
ExampleBase::reportStatus(status, userAgentFileName);
return 1;
ExampleParameters params;
params.dataFilePath = dataFilePath;
params.evidenceFilePath = userAgentFilePath;
// run the example
// Wait for a character to be pressed.
return 0;