modbus_receive_confirmation - Man Page

receive a confirmation request


int modbus_receive_confirmation(modbus_t *ctx, uint8_t *rsp);


The modbus_receive_confirmation() function shall receive a request via the socket of the context ctx. This function must be used for debugging purposes because the received response isn’t checked against the initial request. This function can be used to receive request not handled by the library.

The maximum size of the response depends on the used backend, in RTU the rsp array must be MODBUS_RTU_MAX_ADU_LENGTH bytes and in TCP it must be MODBUS_TCP_MAX_ADU_LENGTH bytes. If you want to write code compatible with both, you can use the constant MODBUS_MAX_ADU_LENGTH (maximum value of all libmodbus backends). Take care to allocate enough memory to store responses to avoid crashes of your server.

Return Value

The function shall store the confirmation request in rsp and return the response length if successful. The returned request length can be zero if the indication request is ignored (eg. a query for another slave in RTU mode). Otherwise it shall return -1 and set errno.


rc = modbus_receive_confirmation(ctx, rsp);

See Also



The libmodbus documentation was written by Stéphane Raimbault <>

Referenced By

libmodbus(7), modbus_send_raw_request(3).

01/25/2024 libmodbus v3.1.7 libmodbus Manual