struct without typedef - cannot use in a pointer-to-member

Question

I have a simple structure and I want a pointer-to-member c. I'm using MSVC2012 and if I don't declare the struct abc as a type definition (typedef), I can't use it.. how come?

struct abc
{
    int a;
    int b;
    char c;
};

char (struct abc)::*ptt1 = &(struct abc)::c; // Error: error C2144: syntax error : 'abc' should be preceded by ')'

typedef struct abc;
char abc::*ptt1 = &abc::c; // Compiles just fine

As explained in stackoverflow.com/questions/2750270/c-c-struct-vs-class, struct is just like class keyword (except the default member visibility), and you wouldn't write &(class abc)::c, would you? :) — FredericS
– FredericS, Commented Mar 21, 2013 at 15:26

Andy Prowl · Accepted Answer · 2013-03-21 12:50:32Z

7

if I don't declare the struct abc as a type definition (typedef), I can't use it.. how come?

You can, and you don't need the struct keyword, nor the typedef. Just do this:

char abc::*ptt1 = &abc::c;

answered Mar 21, 2013 at 12:50

Andy Prowl

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5 Comments

Paul Over a year ago

But to declare a variable of that structure I need to write "struct abc myvariable;", is it correct?

Andy Prowl Over a year ago

@Paul: No, you don't need to. abc myvariable; is enough.

Paul Over a year ago

Today I discovered that I don't need typedef to declare a struct variable... so what's the use of typedef struct abc {..}; ?

Andy Prowl Over a year ago

@Paul: typedef is used to define a type alias. If you have a structure defined as struct abc { ... }; and you want to give it an alternative name, you can do typedef abc other_name;. Then, you can use other_name instead of abc, like: other_name a;. That's equivalent to abc name;. Normally, typedef comes handy to shorten otherwise verbose typenames, e.g. typedef std::map<std::vector<int>, std::string> my_map; my_map m;. Your usage of typedef seems to be a heritage of C, which I do not know quite well. In C++, defining a struct does not require typedef.

Paul Over a year ago

Thank you Andy, in fact I was taught to use typedef in the C fashion but now you helped me greatly. Thank you!

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