All of the command functions in the MIP SDK return a Command Result. Command results are represented by an 8-bit enum type in both C and C++:

Command results are divided into two categories, reply codes and status codes. Reply codes are returned by the device directly:

ACK_OK - Ok; The command was successful.
NACK_COMMAND_UNKNOWN - Unknown command; the descriptor was not recognized or isn't supported.
NACK_INVALID_PARAM - Invalid parameter; One or more parameters are missing, invalid, or not supported.
NACK_COMMAND_FAILED - Command failed; The device was unable to perform the requested function.

The values of these enums match the corresponding values returned by the device in the MIP protocol. They are non-negative 8-bit integers. Please see the documentation for your device for more details.

Status codes are set by this library and are negative 8-bit integers:

STATUS_ERROR - General error, such as failure to send/receive on the connection.
STATUS_TIMEDOUT - Timeout; No response was heard from the device within the specified time period.
Other statuses are used to track commands in progress
STATUS_USER - Application-specific codes can also be set. They must be this value or lower (more negative).

You can use mip_cmd_result_is_reply() / mip::CmdResult::isReplyCode() and mip_cmd_result_is_status() / mip::CmdResult::isStatusCode() to distinguish between the two categories.

In C++, CmdResult is implicitly convertible to bool. ACK_OK converts to true while everything else converts to false. This allows compact code like

if( !mip::commands_base::resume(device) ) // resume returns a CmdResult

std::fprintf(stderr, "Failed to resume the sensor\n");

For debugging, the name of command results is available via mip_cmd_result_to_string() / mip::CmdResult::name

In C++, CmdResult defaults to the initial state CmdResult::STATUS_NONE.