空在计算机编程中是什么意思？

深藏阁楼爱情的钟 2022-12-06 15:44 254阅读 0赞

In computer programming, null is both a value and a pointer. Null is a built-in constant that has a value of zero. It is the same as the character 0 used to terminate strings in C. Null can also be the value of a [pointer][], which is the same as zero unless the [CPU][] supports a special bit pattern for a null pointer.

在计算机编程中，null既是值又是指针。 Null是一个内置常数，值为零。 它与用于终止C中的字符串的字符0相同。Null也可以是[指针][pointer]的值，该值等于零，除非[CPU][]支持null指针的特殊位模式。

## 什么是空值？ **(** What Is a Null Value? **)** ##

In a [database][], zero is a value. The value null means that no value exists. When used as a value, null is not a memory location. Only pointers hold memory locations. Without a null character, a string would not correctly terminate, which would cause problems.

在[数据库中][database] ，零是一个值。 值null表示不存在任何值。 当用作值时，null不是存储位置。 只有指针保存内存位置。 没有空字符，字符串将无法正确终止，这将导致问题。

## 什么是空指针？ **(** What Is a Null Pointer? **)** ##

The C and C++ programming, a pointer is a variable that holds a memory location. The null pointer is a pointer that intentionally points to nothing. If you don't have an address to assign to a pointer, you can use null. The null value avoids memory leaks and crashes in applications that contain pointers. An example of a null pointer in C is:

在C和C ++编程中，指针是保存内存位置的变量。 空指针是故意不指向任何内容的指针。 如果没有要分配给指针的地址，则可以使用null。 null值可避免内存泄漏和包含指针的应用程序崩溃。 C中的空指针的示例是：

int *ptr

printf("The value of ptr is %u

Note: In C, the null macro may have the type void\* but this is not allowed in C++.

注意：在C语言中，null宏的类型可能为void \*，但这在C ++中是不允许的。

## C＃中为Null **(** Null in C\# **)** ##

In C\#, null means "no object." Information about null and its usages in C\# include:

在C＃中，null表示“无对象”。 有关null及其在C＃中的用法的信息包括：

*  You cannot use 0 instead of null in your programs even though null is represented by the value 0.
    
    即使用值0表示null，也不能在程序中使用0而不是null。
 *  You can use null with any reference type including arrays, strings, and custom types.
    
    您可以对任何引用类型(包括数组，字符串和自定义类型)使用null。
 *  In C\#, null is not the same as the constant zero. 
    
    在C＃中，null与常数零不同。

> 翻译自: [https://www.thoughtco.com/definition-of-null-958118][https_www.thoughtco.com_definition-of-null-958118]

[pointer]: https://www.thoughtco.com/understanding-and-using-pointers-in-delphi-1058219
[CPU]: https://www.thoughtco.com/definition-of-compiler-958198
[database]: https://www.thoughtco.com/what-is-a-relational-database-958324
[https_www.thoughtco.com_definition-of-null-958118]: https://www.thoughtco.com/definition-of-null-958118