<anonymous struct> sucks
I think a and b is of the same type and there is no error with the assignment. But the compiler give me an error: incompatible types when assigning to type ‘struct <anonymous>’ from type ‘struct <anonymous>’.Code:int main() { struct { int m_aa; int m_bb; } a = {0, 1}; struct { int m_aa; int m_bb; } b; b = a; // sucks here return 0; }
So how can I make "b = a" legal? (I know memcpy() can do that but that's not what I want. I want to implement std:air<> in C using macros.)
They are different types in C. Even if type,name of fields are the same.
Now the question is why would one want to do this.
That may be a little crazy, but I want to implement syntax-candy like this:Originally Posted by Bayint Naung
Code:MAPITEM_TYPE(int, const char*) mapitem; MAPITEM_KEY(mapitem) = 1; MAPITEM_VAL(mapitem) = "Hello"; AVLTREE_INSERT(tree, mapitem); MAPITEM_KEY(mapitem) = 2; MAPITEM_VAL(mapitem) = "World"; AVLTREE_INSERT(tree, mapitem);
try this....I think a and b is of the same type and there is no error with the assignment. But the compiler give me an error: incompatible types when assigning to type ‘struct <anonymous>’ from type ‘struct <anonymous>’.Code:int main() { struct { int m_aa; int m_bb; } a = {0, 1}; struct { int m_aa; int m_bb; } b; b = a; // sucks here return 0; }
So how can I make "b = a" legal? (I know memcpy() can do that but that's not what I want. I want to implement std:
Now you have two of the same type... and in less code to boot.Code:struct tNums { int m_aa; int m_bb; }; struct tNums a, b;
Last edited by CommonTater; 04-04-2011 at 11:04 AM.
Of course I know that. But I'm trying generic programming in C so I need macros to do that.
For example, now I have an implementation of avltree and want to use it as a dictionary. I have to write a structure first, and define cmp() function for the structure type. That's not convenient. I just want to find an easier way to do that.
You're asking for ugliness!
Note: you need to typedef char* String;Code:#define PAIR_INIT(T1,T2) \ typedef struct { \ T1 first; \ T2 second; \ } pair##T1##T2 #define PAIR(T1,T2) pair##T1##T2 #define make_pair(T1,T2,v1,v2) (pair##T1##T2) { .first = v1, .second = v2 } typedef char * String; PAIR_INIT(String,double); int main(void) { PAIR(String,double) p; p = make_pair(String,double,"foo",3.0); printf("%s %f\n", p.first,p.second); return 0; }
C does not have generic.
I still don't see how generic solves your problem?
Perhaps you should follow C approach. Take a look at bsearch(),qsort(). They are examples of doing generic in C way.
Last edited by Bayint Naung; 04-04-2011 at 11:06 AM.
Also, you can look at the GLIB source. They actually implement a balanced binary tree that takes generic data types, and uses separate key and data elements. Start here: GTK+ - Download.
If you use a typedef template and consistently use only that name for the actual definitions I'm sure it will work. The compiler then has no excuse to think different occurrences of the struct are different in any way.
