# modbus_mapping_new(3) Manual Page

## NAME

modbus_mapping_new - allocate four arrays of bits and registers

## SYNOPSIS

modbus_mapping_t modbus_mapping_new(int nb_bits, int nb_input_bits, int nb_registers, int nb_input_registers);*

## DESCRIPTION

The modbus_mapping_new() function shall allocate four arrays to store bits, input bits, registers and inputs registers. The pointers are stored in modbus_mapping_t structure. All values of the arrays are initialized to zero.

If it isn’t necessary to allocate an array for a specific type of data, you can pass the zero value in argument, the associated pointer will be NULL.

This function is convenient to handle requests in a Modbus server/slave.

## RETURN VALUE

The modbus_mapping_new() function shall return the new allocated structure if successful. Otherwise it shall return NULL and set errno.

## ERRORS

ENOMEM

  Not enough memory

## EXAMPLE

    /* The fist value of each array is accessible from the 0 address. */
    mb_mapping = modbus_mapping_new(BITS_ADDRESS + BITS_NB,
                                    INPUT_BITS_ADDRESS + INPUT_BITS_NB,
                                    REGISTERS_ADDRESS + REGISTERS_NB,
                                    INPUT_REGISTERS_ADDRESS + INPUT_REGISTERS_NB);
    if (mb_mapping == NULL) {
        fprintf(stderr, "Failed to allocate the mapping: %s\n",
                modbus_strerror(errno));
        modbus_free(ctx);
        return -1;
    }

## SEE ALSO

modbus_mapping_free(3)

## AUTHORS

The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com>