CODEWITHSUNDEEP
c++ctypedef
user10600929
user10600929

Reputation:

How to interpret variable declarations with right to left rule while typedef is included?

I am having trouble when using right to left rule to interpret variable declarations when typedef is involved.

In the C++ primer 5th edition book I saw the following code: 

typedef char *pstring;
const pstring cstr = 0; // cstr is a constant pointer to char
const pstring *ps; // ps is a pointer to a constant pointer to char

If I replace the pstring with char * then it stands like this:

const char *cstr

So I expect cstr to be a pointer to a const char. But the comments in the book states the pointer itself is constant. My question is what's wrong with my way of thinking.

Upvotes: 0

Views: 354

Answers (2)

Jefferson
Jefferson

Reputation: 529

As can be read here:

If an array type is declared with the const type qualifier (through the use of typedef), the array type is not const-qualified, but its element type is

Because pstring is typedef to char *, const pstring cstr is char * const cstr, not const char * cstr.

Upvotes: 1

Artyer
Artyer

Reputation: 40826

A typedef is not a macro. You don't just text replace it.

Read it as cstr is a "constant pstring", which is a "constant (pointer to char)". Compare this to const char*, which is "pointer to constant char".

If you were to replace the typedef it would look like this:

char* const cstr = 0;
char* const* ps;

Upvotes: 2

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