nullptr has type std::nullptr_t. It’s implicitly convertible to any pointer type. Thus, it’ll match std::nullptr_t or pointer types in overload resolution, but not other types such as int. 0 (aka. C’s NULL bridged over into C++) could cause ambiguity in overloaded function resolution, among other things: f(int); f(foo *); (Thanks to Caleth pointing this out … Read more
For normal DateTimes, if you don’t initialize them at all then they will match DateTime.MinValue, because it is a value type rather than a reference type. You can also use a nullable DateTime, like this: DateTime? MyNullableDate; Or the longer form: Nullable<DateTime> MyNullableDate; And, finally, there’s a built in way to reference the default of … Read more
[Updated to adapt to modern pandas, which has isnull as a method of DataFrames..] You can use isnull and any to build a boolean Series and use that to index into your frame: >>> df = pd.DataFrame([range(3), [0, np.NaN, 0], [0, 0, np.NaN], range(3), range(3)]) >>> df.isnull() 0 1 2 0 False False False 1 … Read more
SQL NULL’s special, and you have to do WHERE field IS NULL, as NULL cannot be equal to anything, including itself (ie: NULL = NULL is always false). See Rule 3 https://en.wikipedia.org/wiki/Codd%27s_12_rules
The default for ResultSet.getInt when the field value is NULL is to return 0, which is also the default value for your iVal declaration. In which case your test is completely redundant. If you actually want to do something different if the field value is NULL, I suggest: int iVal = 0; ResultSet rs = … Read more
Postgres 15 or newer Postgres 15 (currently beta) adds the clause NULLS NOT DISTINCT. The release notes: Allow unique constraints and indexes to treat NULL values as not distinct (Peter Eisentraut) Previously NULL values were always indexed as distinct values, but this can now be changed by creating constraints and indexes using UNIQUE NULLS NOT … Read more
test=”categoryName != ”” Edit: This covers the most likely interpretation, in my opinion, of “[not] null or empty” as inferred from the question, including it’s pseudo-code and my own early experience with XSLT. I.e., “What is the equivalent of the following Java?”: // Equivalent Java, NOT XSLT !(categoryName == null || categoryName.equals(“”)) For more details … Read more
<> is Standard SQL-92; != is its equivalent. Both evaluate for values, which NULL is not — NULL is a placeholder to say there is the absence of a value. Which is why you can only use IS NULL/IS NOT NULL as predicates for such situations. This behavior is not specific to SQL Server. All … Read more
You can safely use the typeof operator on undefined variables. If it has been assigned any value, including null, typeof will return something other than undefined. typeof always returns a string. Therefore if (typeof maybeObject != “undefined”) { alert(“GOT THERE”); }
Note: This answer applies to the C language, not C++. Null Pointers The integer constant literal 0 has different meanings depending upon the context in which it’s used. In all cases, it is still an integer constant with the value 0, it is just described in different ways. If a pointer is being compared to … Read more