22.1.4.3 Type qualifiers on array parameters

You can use the type qualifiers const, restrict, and volatile with array parameters; for example:

void
clobber4 (volatile int array[20])
…

denotes that array is equivalent to a pointer to a volatile int. Alternatively:

void
clobber4 (int array[const 20])
…

makes the array parameter equivalent to a constant pointer to an int. If we want the clobber4 function to succeed, it would not make sense to write

void
clobber4 (const int array[20])
…

as this would tell the compiler that the parameter should point to an array of constant int values, and then we would not be able to store zeros in them.

In a function with multiple array parameters, you can use restrict to tell the compiler that each array parameter passed in will be distinct:

void
foo (int array1[restrict 10], int array2[restrict 10])
…

Using restrict promises the compiler that callers will not pass in the same array for more than one restrict array parameter. Knowing this enables the compiler to perform better code optimization. This is the same effect as using restrict pointers (see restrict Pointers), but makes it clear when reading the code that an array of a specific size is expected.