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The C standard defines that 0 cast to the type void * is both a null pointer and a null pointer constant. Additionally, to help readability, the macro NULL is provided in the header file stddef.h. Depending upon your compiler it might be possible to #undef NULL and redefine it to something wacky.
4 mar 2011 · Conceptually, zero (0) is a number, and NULL is a value that represents "no value". As such, 0 can be added, subtracted, etc., but NULL cannot. The NULL value for a variable can indicate, for example, that a variable has not yet been assigned a value.
14 lut 2012 · The basic difference is that 0 is about measurable quantity, while NULL is about existence. Being a quantity, 0 represents something, i.e. a quantity, that is 0, much like 0.000000001 represents a quantity (one that in problems of every day life is in fact indistinguishably close to 0).
17 lip 2024 · Aby spełnić wymagania prawdziwych systemów zarządzania relacyjnymi bazami danych, MySQL używa NULL jako symbolu zastępczego wartości, które nie zostały przesłane. Poniższy zrzut ekranu pokazuje, jak wartości NULL wyglądają w bazie danych.
12 cze 2018 · The value 0 (all bits at zero) is a typical value used in memory to denote null. It means that there is no value associated with name . You can also think of it as the absence of data or simply no data .
null and zero are used in many contexts where they have different meanings. In math you can have a set with no items in it (a null set) or you can have a set with a zero in it ({ 0 }) which are not the same. In programming some languages make null the same as zero (C++) but some don't (Java).
In MySQL, 0 or NULL means false and anything else means true. The default truth value from a boolean operation is 1. NULL instead of death <>. NULL. Two NULL values are regarded as equal in a GROUP BY. When doing an ORDER BY, NULL values are presented first if you do ORDER BY ... ASC and last if you do ORDER BY ...
