Environment Variables

EnvVar

class canlib.canlib.EnvVar(channel)

Used to access environment variables in t programs.

The environment variables are accessed as an attribute with the same name as declared in the t program. If we have a running t program, which has defined the following environment variables:

envvar
{
  int   IntVal;
  float FloatVal;
  char  DataVal[512];
}

We access the first two using EnvVar:

>>> ch.envvar.IntVal
0
>>> ch.envvar.IntVal = 3
>>> ch.envvar.IntVal
3
>>> ch.envvar.FloatVal
15.0

The third environment variable, declared as char*, is accessed using DataEnvVar.

DataEnvVar

class canlib.canlib.envvar.DataEnvVar(channel, handle, name, size)

Represent an environment variable declared as char* in t programs.

This attribute object behaves like an array of bytes:

>>> ch.envvar.DataVal[100:141]
b'ot working? Messages can be sent to and r'

The size of the array must match what was defined in the t program. One way to do this is to left align the data and fill with zeros:

>>> data = 'My new data'.encode('utf-8')
>>> size = len(ch.envvar.DataVal)
>>> ch.envvar.DataVal = data.ljust(size, b'\0')
>>> ch.envvar.DataVal[:15]
b'My new data\x00\x00\x00\x00'

Another way is to use slicing:

>>> ch.envvar.DataVal[3:6] = b'old'
>>> ch.envvar.DataVal[:15]
b'My old data\x00\x00\x00\x00'