* []和**之间的C差异 [英] C difference between *[] and **

问题描述

这可能是一个基本问题，但是写char * []和char **有什么区别?例如，在main中，我可以有一个char * argv [].另外，我可以使用char ** argv.我认为这两种表示法之间肯定会有某种区别.

This might be a bit of a basic question, but what is the difference between writing char * [] and char **? For example, in main,I can have a char * argv[]. Alternatively I can use char ** argv. I assume there's got to be some kind of difference between the two notations.

推荐答案

在这种情况下，没有任何区别.如果您尝试将数组类型用作函数参数，则编译器会将其调整"为指针类型(即T a[x] 作为函数参数表示完全 >与T *a)相同.

Under the circumstances, there's no difference at all. If you try to use an array type as a function parameter, the compiler will "adjust" that to a pointer type instead (i.e., T a[x] as a function parameter means exactly the same thing as: T *a).

在适当的情况下(即， not 作为函数参数)，使用数组和指针表示法之间可能会有区别. extern声明是一种常见的声明.例如，假设我们有一个文件，其中包含以下内容:

Under the right circumstances (i.e., not as a function parameter), there can be a difference between using array and pointer notation though. One common one is in an extern declaration. For example, let's assume we have one file that contains something like:

char a[20];

，我们想在另一个文件中显示该内容.这将起作用:

and we want to make that visible in another file. This will work:

extern char a[];

但这不会:

extern char *a;

如果我们改为使用指针数组:

If we make it an array of pointers instead:

char *a[20];

...同样如此-声明一个extern数组很好，但是声明一个extern指针却不能:

...the same remains true -- declaring an extern array works fine, but declaring an extern pointer does not:

extern char *a[]; // works

extern char **a;   // doesn't work

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