51Degrees Device Detection C/C++  4.5

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

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Hash/ReloadFromMemory.cpp

Reload from file example of using 51Degrees device detection.

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 data file that has been read into a continuous memory space.
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 resource with initialized dataset. Function reloads the dataset from the provided pointer to the continuous memory space containing the data file. New dataset is created 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: /Support/Documentation/APIs/C-V32/Benchmarks?utm_source=code&utm_medium=example&utm_campaign=51degrees-cxx&utm_content=examples-cpp-hash-reloadfrommemory.cpp&utm_term=header

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* Copyright 2026 51 Degrees Mobile Experts Limited, Davidson House,

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// 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 "ExampleBase.hpp"

using namespace FiftyoneDegrees::Examples::Hash;

namespace FiftyoneDegrees {

namespace Examples {

namespace Hash {

class ReloadFromMemory : public ExampleBase {

public:

ReloadFromMemory(

byte* data,

long length,

string userAgentFilePath,

DeviceDetection::Hash::ConfigHash *config)

: ExampleBase(data, length, config) {

this->data = data;

this->length = length;

this->userAgentFilePath = userAgentFilePath;

};

void run() {

int numberOfReloads = 0;

int numberOfReloadFails = 0;

ExampleBase::SharedState state(engine, userAgentFilePath);

if (fiftyoneDegreesThreadingGetIsThreadSafe()) {

printf("** Multi Threaded Reload Example **\r\n");

state.startThreads();

while (state.threadsFinished < THREAD_COUNT) {

try {

engine->refreshData(data, length);

numberOfReloads++;

}

catch (StatusCodeException&) {

numberOfReloadFails++;

}

#ifdef _MSC_VER

Sleep(2000); // milliseconds

#else

usleep(20000000); // microseconds

#endif

}

state.joinThreads();

}

else {

printf("** Single Threaded Reload Example **\r\n");

state.processUserAgentsSingle();

try {

engine->refreshData(data, length);

numberOfReloads++;

}

catch (StatusCodeException&) {

numberOfReloadFails++;

}

state.processUserAgentsSingle();

}

// 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.");

}

private:

string userAgentFilePath;

byte *data;

long length;

};

}

}

}

extern "C" void fiftyoneDegreesExampleCPPReloadFromMemoryRun(ExampleParameters *params) {

// Call the actual function.

DeviceDetection::Hash::ConfigHash *cppConfig = new DeviceDetection::Hash::ConfigHash();

cppConfig->setConcurrency(THREAD_COUNT);

// Read the data file into memory for the initialise and reload operations.

fiftyoneDegreesMemoryReader reader;

fiftyoneDegreesStatusCode status = fiftyoneDegreesFileReadToByteArray(

params->dataFilePath, &reader);

if (status != FIFTYONE_DEGREES_STATUS_SUCCESS) {

ExampleBase::reportStatus(status, params->dataFilePath);

exit(1);

}

try {

ReloadFromMemory *reloadFromMemory = new ReloadFromMemory(

reader.startByte,

reader.length,

params->evidenceFilePath,

cppConfig);

reloadFromMemory->run();

delete reloadFromMemory;

}

catch (const StatusCodeException &e) {

// The engine only has the memory, so the file name is added here.

ExampleBase::reportStatus(e.getCode(), params->dataFilePath);

exit(1);

}

// Free the memory for the test.

fiftyoneDegreesFree(reader.startByte);

}

#ifndef TEST

int main(int argc, char* argv[]) {

fiftyoneDegreesStatusCode status = FIFTYONE_DEGREES_STATUS_SUCCESS;

char dataFilePath[FIFTYONE_DEGREES_FILE_MAX_PATH];

char userAgentFilePath[FIFTYONE_DEGREES_FILE_MAX_PATH];

if (argc > 1) {

strcpy(dataFilePath, argv[1]);

}

else {

status = ExampleBase::getFilePath(

dataDir,

dataFileName,

dataFilePath,

sizeof(dataFilePath));

}

if (status != FIFTYONE_DEGREES_STATUS_SUCCESS) {

ExampleBase::reportStatus(status, dataFileName);

fgetc(stdin);

return 1;

}

if (argc > 2) {

strcpy(userAgentFilePath, argv[2]);

}

else {

status = ExampleBase::getFilePath(

dataDir,

userAgentFileName,

userAgentFilePath,

sizeof(userAgentFilePath));

}

if (status != FIFTYONE_DEGREES_STATUS_SUCCESS) {

ExampleBase::reportStatus(status, userAgentFileName);

fgetc(stdin);

return 1;

}

ExampleParameters params;

params.dataFilePath = dataFilePath;

params.evidenceFilePath = userAgentFilePath;

// run the example

fiftyoneDegreesExampleMemCheck(

&params,

fiftyoneDegreesExampleCPPReloadFromMemoryRun);

// Wait for a character to be pressed.

fgetc(stdin);

return 0;

}

#endif

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