C ++编译器读取“ int * p”时在做什么？

Question

What is the compiler doing when it reads "int *p?" Does it assume p will become a pointer to an array of integers? Can the star operator only be used with arrays?

Answer 1

In C and C++, arrays and pointers are related to each other. In particular, this means that p can be made to point to a single int , or to the first element of an array of ints .

Answer 2

Does it assume p will become a pointer to an array of integers?

No. It will allow p to hold the address of any integer.

It doesn't assume that it will. And if it does, it doesn't assume that it will be an array.

Answer 3

What is the compiler doing when it reads "int *p?"

This will set up a variable called p which is a pointer to an integer.

Does it assume p will become a pointer to an array of integers?

No.

p could just point to a single integer, though following (and even preceding) integer values could be accessed by using subsequent (or preceding) pointer values. So it could also be pointing to the first element of an array of integers.

*p or p[0] will return the integer at the end of the pointer

*(p + 1) or p[1] will return the integer immediately after the integer at the end of the pointer.

*(p - 1) or p[-1] will return the integer immediately before the integer at the end of the pointer.

(In fact there is a thing which is a "pointer to an array of integers", which has its own syntax (eg "int (*p)[10];") which has its own meaning, but that is a topic for another question.)

Can the star operator only be used with arrays?

The star operator is used to refer to the value and the end of the pointer, either for reading or writing.

So whilst it is convenient for accessing sequences (arrays) of values, it can also be used to access a single value to get pass-by-reference semantics.

Answer 4

Here's an example that may help:

#include <stdio.h>

main()
{
    int i = 10;
    int ia[2] = {1,2};

    int *p;
    p = &i;
    printf("%d\n", *p);
    p = ia;
    printf("%d\n", *p);
}

The output is 10 followed by 1.