In C, is it good form to use typedef for a pointer?

Question

Consider the following C code:

typedef char * MYCHAR;
MYCHAR x;

My understanding is that the result would be that x is a pointer of type "char". However, if the declaration of x were to occur far away from the typedef command, a human reader of the code would not immediately know that x is a pointer. Alternatively, one could use

typedef char MYCHAR;
MYCHAR *x;

Which is considered to be better form? Is this more than a matter of style?

Answer 1

If the pointer is never meant to be dereferenced or otherwise manipulated directly -- IOW, you only pass it as an argument to an API -- then it's okay to hide the pointer behind a typedef.

Otherwise, it's better to make the "pointerness" of the type explicit.

Answer 2

I would use pointer typedefs only in situations when the pointer nature of the resultant type is of no significance. For example, pointer typedef is justified when one wants to declare an opaque "handle" type which just happens to be implemented as a pointer, but is not supposed to be usable as a pointer by the user.

typedef struct HashTableImpl *HashTable;
/* 'struct HashTableImpl' is (or is supposed to be) an opaque type */

In the above example, HashTable is a "handle" for a hash table. The user will receive that handle initially from, say, CreateHashTable function and pass it to, say, HashInsert function and such. The user is not supposed to care (or even know) that HashTable is a pointer.

But in cases when the user is supposed to understand that the type is actually a pointer and is usable as a pointer, pointer typedefs are significantly obfuscating the code. I would avoid them. Declaring pointers explicitly makes code more readable.

It is interesting to note that C standard library avoids such pointer typedefs. For example, FILE is obviously intended to be used as an opaque type, which means that the library could have defined it as typedef FILE <some pointer type> instead of making us to use FILE * all the time. But for some reason they decided not to.

Answer 3

I don't particularly like typedef to a pointer, but there is one advantage to it. It removes confusion and common mistakes when you declare more than one pointer variable in a single declaration.

typedef char *PSTR;
...
PSTR str1, str2, str3;

is arguably clearer than:

char *str1, str2, str3;  // oops