C difference between *[] and **

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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).

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];

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

extern char a[];

but this will not:

extern char *a;

If we make it an array of pointers instead:

char *a[20];

…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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