Recently I have been using the := operator in python quite a bit, in this way:

if my_object := SomeClass.function_that_returns_object():
    # do something with this object if it exists
    print(my_object.some_attribute)

The question

Is there any way to do this in c++11 without the use of stdlib? for example in an arduino sketch if I wanted to use a method that may potentially return zero, such as:

if(char * data = myFile.readBytes(data, dataLen))
{
    // do something
}
else
{
    // do something else
}

Python's := assignment expression operator (aka, the "walrus" operator) returns the value of an assignment.

C++'s = assignment operator (both copy assignment and move assignment, as well as other assignment operators) does essentially the same thing, but in a different way. The result of an assignment is a reference to the object that was assigned to, allowing that object to be evaluated in further expressions.

So, the equivalent of:

if my_object := SomeClass.function_that_returns_object():
    # do something with this object if it exists
    print(my_object.some_attribute)

Would be just like you showed:

SomeType *my_object;
if ((my_object = SomeClass.function_that_returns_object())) {
    // do something with this object if it exists
    print(my_object->some_attribute);
}

If function_that_returns_object() returns a null pointer, the if evaluates my_object as false, otherwise it evaluates as true. The same can be done with other types, eg:

int value;
if ((value = SomeClass.function_that_returns_int()) == 12345) {
    // do something with this value if it matches
}