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区分const指针

2015-07-05 23:37 183 查看

Read it backwards...

int*

- pointer to int

int const *

- pointer to const int

int * const

- const pointer to int

int const * const

- const pointer to const int

Now the first const can be on either side of the type so:

const int *

int const *

const int * const

int const * const

If you want to go really crazy you can do things like this:

int **

- pointer to pointer to int

int ** const

- a const pointer to a pointer to an int

int * const *

- a pointer to a const pointer to an int

int const **

- a pointer to a pointer to a const int

int * const * const

- a const pointer to a const pointer to an int

...

And to make sure we are clear on the meaning of const

const int* foo;
int *const bar; //note, you actually need to set the pointer
//here because you can't change it later ;)

foo

is a variable pointer to a constant int. This lets you change what you point to but not the value that you point to. Most often this is seen with cstrings where you have a pointer to a

const char

. You may change which string you point to but you can't change the content of these strings. This is important when the string itself is in the data segment of a program and shouldn't be changed.

bar

is a const or fixed pointer to a value that can be changed. This is like a reference without the extra syntactic sugar. Because of this fact, usually you would use a reference where you would use a

T* const

pointer unless you need to allow null pointers.

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