Examples EnvironmentControl

EnvironmentControl

EnvironmentControl

This example shows explicit startup control from process environment variables.

Environment control is disabled unless the application calls ApplyEnvironmentControl(). For generated documentation and simple local runs, the example is self-contained: if LOGME_CONTROL is not already set, the example sets it internally before calling ApplyEnvironmentControl().

The demo channel env_example is initially disabled. Messages sent to it before ApplyEnvironmentControl() are not printed. The environment command enables the channel and changes its level to debug, so the messages printed after ApplyEnvironmentControl() become visible.

Default demo command:

LOGME_CONTROL="channel --enable env_example; level --channel env_example debug"

You can override it from the shell:

LOGME_CONTROL="channel --enable env_example; level --channel env_example info" ./EnvironmentControl

The string may contain multiple control commands separated by ;. Each command is executed through the normal control API and is checked by the policy passed to ApplyEnvironmentControl().

Console output

2026-06-10 14:51:43:498   main(): Environment control example
2026-06-10 14:51:43:498   main(): env_example channel is disabled before ApplyEnvironmentControl()
2026-06-10 14:51:43:498   main(): LOGME_CONTROL is set to: channel --enable env_example; level --channel env_example debug
2026-06-10 14:51:43:498   main(): env_example channel is controlled by environment commands now
2026-06-10 14:51:43:498 D main(): debug message after environment control
2026-06-10 14:51:43:498   main(): info message after environment control

Source code

Sources

Repository folder: examples/EnvironmentControl

EnvironmentControl.cpp

Open in repository

#include <Logme/Logme.h>

#include <cstdlib>
#include <string>

static Logme::ID EnvExampleChannel{ "env_example" };

static void SetEnvironmentVariable(
  const std::string& name
  , const std::string& value
)
{
#ifdef _WIN32
  _putenv_s(name.c_str(), value.c_str());
#else
  setenv(name.c_str(), value.c_str(), 1);
#endif
}

static std::string GetEnvironmentVariable(const std::string& name)
{
#ifdef _WIN32
  char* value = nullptr;
  size_t size = 0;

  errno_t error = _dupenv_s(&value, &size, name.c_str());
  if (error != 0 || value == nullptr)
  {
    return std::string();
  }

  std::string result(value);
  std::free(value);
  return result;
#else
  const char* value = std::getenv(name.c_str());
  if (value == nullptr)
  {
    return std::string();
  }

  return std::string(value);
#endif
}

static void SetupDemoEnvironment()
{
  std::string value = GetEnvironmentVariable("LOGME_CONTROL");
  if (!value.empty())
  {
    return;
  }

  SetEnvironmentVariable(
    "LOGME_CONTROL"
    , "channel --enable env_example; level --channel env_example debug"
  );
}

static Logme::ChannelPtr CreateExampleChannel()
{
  auto defaultChannel = Logme::Instance->GetDefaultChannelPtr();
  defaultChannel->SetFilterLevel(Logme::LEVEL_DEBUG);

  auto channel = Logme::Instance->CreateChannel(EnvExampleChannel);
  channel->AddLink(::CH);
  channel->SetFilterLevel(Logme::LEVEL_INFO);
  channel->SetEnabled(false);
  return channel;
}

int main()
{
  CreateExampleChannel();

  LogmeI("Environment control example");
  LogmeI("env_example channel is disabled before ApplyEnvironmentControl()");

  LogmeD(EnvExampleChannel, "debug message before environment control");
  LogmeI(EnvExampleChannel, "info message before environment control");

  SetupDemoEnvironment();

  std::string control = GetEnvironmentVariable("LOGME_CONTROL");
  LogmeI("LOGME_CONTROL is set to: %s", control.c_str());

  Logme::EnvironmentControlOptions options;
  options.Prefix = "LOGME";
  options.Policy = Logme::ControlPolicy::Safe();
  options.ErrorMode = Logme::EnvironmentControlErrorMode::CONTINUE_ON_ERROR;

  Logme::Instance->ApplyEnvironmentControl(options);

  LogmeI("env_example channel is controlled by environment commands now");
  LogmeD(EnvExampleChannel, "debug message after environment control");
  LogmeI(EnvExampleChannel, "info message after environment control");

  return 0;
}

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