Using the C API

The C API libraries come with C-header files and shared objects. The libmxidaf API provides pkg-config support to compile your source code, which you can use as follows:

$ gcc -c example.c -o example.o `pkg-config --cflags`

To link your code, use the following command:

$ gcc -o example example.o `pkg-config --libs`

Initializing the Tag Library

To initialize the tag library, create a tag instance.

To create a tag instance in C, use the following command:

tag *tag_inst = tag_new();

Deleting a Tag Instance

To delete a Tag instance in C, use the following command:

tag_delete(tag_inst);

Publishing Tags

To publish tags, use tag_publish().

value_t value_data;
value_data.d = 1.38;

int rc = tag_publish(
    tag_inst,
    "Equipment-Name",
    "Tag-Name",
    value_data,
    TAG_VALUE_TYPE_DOUBLE,
    "",
    "2016-09-20T11:11:40Z");

Sample

A sample application is available at:

/usr/share/mxdaf/libmxidaf/sample/publish.c

Subscribing to Tags

To subscribe to Tags, use tag_subscribe() or tag_subscribe_callback() as follows:

tag_subscribe(
    tag_inst,
    "Subscribe_Equipment",
    "SubScribe_Tag");

void my_callback_func(
    tag *tag_inst,
    const char *equipment_name,
    const char *tag_name,
    value_t *value,
    value_type_t value_type,
    const char *unit,
    const char *timestamp)
{
}

tag_subscribe_callback(
    tag_inst,
    my_callback_func);

Sample

A sample application is available at:

/usr/share/mxdaf/libmxidaf/sample/subscribe.c

Initializing the Modbus Library

To initialize the modbus library, create a mxmodbus instance.

To create a mxmodbus instance in C, use the following command:

mxmodbus *mxmodbus_inst = mxmodbus_new();

Deleting a Modbus Library Instance

To delete a mxmodbus instance in C, use the following command:

mxmodbus_delete(mxmodbus_inst);

Reading Modbus Tags

To read Modbus Tags, use mxmodbus_read().

#define MODBUS_READ_TIMEOUT_MS 1000

value_t value_data;
value_type_t value_type;

int rc = mxmodbus_read(
    mxmodbus_inst,
    "Equipment-Name",
    "Tag-Name",
    MODBUS_READ_TIMEOUT_MS,
    &value_data,
    &value_type
);

Sample

A sample application is available at:

/usr/share/mxdaf/libmxidaf/sample/modbus.c

Writing Values into Modbus Tags

To write values into Modbus Tags, use mxmodbus_write().

#define MODBUS_WRITE_TIMEOUT_MS 1000

value_t value_data;
value_data.d = 1.38

int rc = mxmodbus_write(
    mxmodbus_inst,
    "Equipment-Name",
    "Tag-Name",
    MODBUS_WRITE_TIMEOUT_MS,
    value_data,
    TAG_VALUE_TYPE_DOUBLE
);

Sample

A sample application is available at:

/usr/share/mxdaf/libmxidaf/sample/modbus.c