Loggers record data from a data signal and are represented by the MblMwDataLogger struct. Create an MblMwDataLogger object by calling mbl_mw_datasignal_log with the data signal you want to log. If successful, the callback function will be executed with a MblMwDataLogger pointer and if creating the logger failed, a null pointer will be returned.

#include "metawear/core/datasignal.h"
#include "metawear/core/logging_fwd.h"
#include "metawear/sensor/multichanneltemperature.h"

auto temp_signal = mbl_mw_multi_chnl_temp_get_temperature_data_signal(board, 0);
mbl_mw_datasignal_log(temp_signal, [](MblMwDataLogger* logger) -> void {
    if (logger != nullptr) {
        printf("logger ready\n");
    } else {
        printf("Failed to create the logger\n");

MblMwDataLogger objects only interact with the specific data signal, they do not control the logging features. Logging control functions are detailed in the Logging section.


MblMwDataLogger objects are identified by a numerical id; you can retrieve the id by calling mbl_mw_logger_get_id. The id is used to retrieve existing loggers from the API with the mbl_mw_logger_lookup_id function.

Handling Data

Like a data signal, you can subscribe to an MblMwDataLogger to process the downloaded data. Call mbl_mw_logger_subscribe to attach a callback function to the MblMwDataLogger which handles all received data.

void logger_subscribe(MblMwDataLogger* temp_logger) {
    mbl_mw_logger_subscribe(temp_logger, [](const MblMwData* data) -> void {
        printf("temperature= %.3fC\n", *((float*) data->value));


When you no longer want to log the values from a data signal, call mbl_mw_logger_remove to remove the logger.