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Reference to a constant pointer

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Started by adder_noir October 11, 2010 12:56 PM

2 comments, last by adder_noir 13 years, 6 months ago

adder_noir

275

Author

October 11, 2010 12:56 PM

Hi,

Still reading thru my intermediate book I've hit the latest snag. He's talking about constant pointers and references. Here's the code:

const T *const cpct1 = pt;.... sometime laterconst T &rct = *pt;

now from what I understand he is declaring constant variable 'T'. Then he's declaring a reference which is to be an alias for this variable 'rct'. The next bit *looks* to me like a de-referencing operation. Can I ask though in the first line by declaring a pointer to T 'pt' has he also created an 'object' T. I can't - in the second line - see how I can have a reference aliasing a variable that does not yet exist and I didn't see a 'new' command used anywhere.

Am I talking bull? Help please if possible, thanks ;o)

Zao

988

October 11, 2010 01:11 PM

const T *const cpct1 = pt;

declares a variable named

cpctl

of type const-pointer-to-const-T, and assigns it the value of the (assumedly of pointer type) variable pt.

const T &rct = *pt;

declares a variable named

rct

of type reference-to-const-T, and initializes it with the variable at the address pointed to by the pointer pt.

Types are normally read right-to-left to make sense, apart from the wart that a leftmost const is as if it was to the right of the component to the right.

That is, "T const**" and "const T**" are the same type.

To make it is hell. To fail is divine.

rip-off

11,000

October 11, 2010 01:13 PM

There isn't enough code. It all depends on "pt". The author might be talking about a pointer to an existing T instance (allocated dynamically or on the stack). You don't need to use "new" to get an object:

T instance;const T *const pointer = &instance;const T &reference = *pointer;

If "pt" is uninitialised or is NULL, then the line that dereferences it is undefined behaviour.

Also the book is probably terrible if those are the actual variable names it uses.

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adder_noir

275

Author

October 11, 2010 02:05 PM

Thanks to you both for very good replies. So I wasn't totally out of my tree then! Rip-off you seem a pretty solid guy, can you recommend a decent book then for someone at my experience level. I intentionally went after an intermediate level C++ book. It can be a bit heavy going and a bit weird in places ;o)

Reference to a constant pointer

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