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Pointers, const, constexpr and Type Aliases

程序员文章站 2024-02-29 19:32:34
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Generally, it's best to read from right to left to understand a declearation.

const double *cptr = π

would read like:

pointer to const double

meaning we cannot use the pointer to modify underlying double variable.

int *const currErr = &errNumb;

reads:

const pointer to int

meaning the value of the pointer (i.e. the address it holds) cannot change.

some more complicated cases:

const double *const ppi = π // const pointer to const double

constexpr and type aliases brings some new problem dimemsions.

const int *p = nullptr; // pointer to const int
constexpr int *q = nullptr; // a { (const) pointer to int } as a const expression
constexpr const int *p2 = &i; // a { (const) pointer to const int } as a const expression

In a way, constexpr implies a top-level const

Type aliases also yield complicated cases:

typedef char *pstring;
const pstring cstr = 0; // const pstring i.e. const pointer to char
const pstring *ps; // pointer to const pstring i.e. pointer to const pointer to char

note replacing type aliases with the corresponding type will result in incorrect result:

const char *cstr = 0; // pointer to const char

this is different from const pstring

 

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