What does Null mean?

What does null mean in Chinese? I believe many people have seen null in C, SQL and PHP. However, novices don’t understand null very well. Let’s summarize what Null means?

What does Null mean?

NULL is a reserved value in calculations and is used to indicate that the pointer does not refer to a valid object. Programs often use null pointers to represent conditions, such as the end of a list of unknown length or that some operation was not performed; this use of null pointers can be compared with the Nothing value in nullable and option types.

Null is a reserved value in the computer and can be used as a pointer without referencing an object. Many programs now use pointers to express conditions, but in different languages, the meaning is different.

1.c

We all know that Null inherits the Null macro in c. However, the pointer constant is an integer 0. Many people think that the null pointer takes precedence over the pointer value, so in A constant is quoted in c instead.

2.SQL

In the database, the Null function means that there is no value for a certain field, and it means that the field value is empty. Null and The other fields have different values ​​and no field values ​​are stored. I don’t know what the data is, I don’t know what the specific value is, and I don’t know if the data really exists.

3.PHP

In PHP 4, NULL was introduced. NULL means that there is no value in a variable. Many people think that it is assigned a value. The value is NULL, including those that have not been assigned a value, and those that have been unset().

4.JAVA

In JAVA, NULL represents a keyword, which is often used to represent a null reference.

The above is the complete introduction to what it means to learn Null. If you want to know more about Getting Started with PHP Programming, please pay attention to the PHP Chinese website.

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