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2. python - How do I check if a variable exists? - Stack Overflow

   stackoverflow.com/questions/843277

   Using try/except is the best way to test for a variable's existence. But there's almost certainly a better way of doing whatever it is you're doing than setting/testing global variables. For example, if you want to initialize a module-level variable the first time you call some function, you're better off with code something like this:

3. c++ - C++20 concepts how to define existence of a function with...

   stackoverflow.com/questions/62058820

   In C++20, we can now use concepts instead of SFINAE to figure out whether a function exists in a template typename: template<typename T> concept fooable = requires (T a) { a.foo(); }; c...

4. JavaScript check if variable exists (is defined/initialized)

   stackoverflow.com/questions/5113374

   The above is true when using var to define a variable, as opposed to let which: declares a block scope local variable, optionally initializing it to a value. is unlike the var keyword, which defines a variable globally, or locally to an entire function regardless of block scope.

5. C++: Which is the best method of checking for file existence on...

   stackoverflow.com/questions/4403986

   There are two things to consider here: Checking if the file exists via its attributes is potentially many orders of magnitude faster - If a file exists on a 'slow' file system - tape, network storage, cd etc then opening the file will involve an actual round trip to the files location.

6. How to check existence of user-define table type in SQL Server...

   stackoverflow.com/questions/2495119

   I have a user-defined table type. I want to check it's existence before editing in a patch using OBJECT_ID(name, type) function. What type from the enumeration should be passed for user-defined table types? N'U' like for user defined table doesn't work, i.e. IF OBJECT_ID(N'MyType', N'U') IS NOT NULL

7. c++ - C++20 concept which requires the existence of an exact...

   stackoverflow.com/questions/64146257

   So my question is: is there a way to require the existence of a function with exact signature in a concept (i.e. the existence of std::abs(T x) and not only the fact that std::abs(x) compiles). Note: The above example is mostly for illustration and could, at least for my application, be fixed by constraining the return type using requires (T x ...

8. Example of a strong and weak entity types - Stack Overflow

   stackoverflow.com/questions/4741967

   The apartment is a weak entity because it cannot exist without the existence of its Identifying Owner, the Building entity. Weak entities are not given primary keys. Instead, the partial identifier, denoted by the dashed line under DoorNo (Door number) attribute, is combined with the BNo. primary key attribute from the Buliding entity to form a ...

9. shell - How to check if a variable is set in Bash - Stack...

   stackoverflow.com/questions/3601515

   Omitting the colon results in a test only for a parameter that is unset. Put another way, if the colon is included, the operator tests for both parameter’s existence and that its value is not null; if the colon is omitted, the operator tests only for existence. It makes no difference here, but good to know. –

10. java - variable scoping - Stack Overflow

    stackoverflow.com/questions/13058193

    Assume the existence of a Phone class. Define a subclass, CameraPhone that contains two instance variables: an integer named, imageSize, representing the size in megapixels (for simplicity assume a pixel takes up one byte-- thus megapixels equals megabytes) of each picture (i.e., 2 means each image is composed of 2 megapixels), and an integer ...

11. Can the C preprocessor be used to tell if a file exists?

    stackoverflow.com/questions/142877

    +1 for making the source code itself fully portable. I think this (or rather in my typical cases a modification where the file is assumed to exist by default and people can signal if they don't have the file) might even be my most preferred method of the ones I see here, because it's trivial to document the defines, and the typical user building from source can already be expected to know or ...