Question

#include<iostream> class name { public:     int a;     name():a(0){}; }; void add(name * pname) {     pname = NULL; } int main() {     name varName();     name * pName = new name();     add(pName);     add(&varName);//error C2664: 'add' : cannot convert parameter 1 from 'name __cdecl *)(void)' to 'name *' } 

Answer 1

I think it’s worth telling you about a similar problem, that also causes trouble:

struct foo { }; struct bar { bar(foo f); };  int main() {   // does *not* create a bar object initialized by a default constructed    // foo object.   bar b(foo()); } 

What b really is is a function that returns a bar and takes as first argument a pointer to a function that returns a foo taking no arguments. It’s the same as:

bar b(foo(*)()); 

If you want to create a bar object initialized by a default constructed foo, put parentheses around the argument. That makes it doesn’t look like a function declaration anymore, and the compiler will interpret it like you want:

bar b((foo())); 

---

There are also non-obvious cases where a compiler error should be risen. GCC gets this wrong, but Comeau gets it right again. Consider the following snippet

struct foo {   static bool const value = false; };  int main() {   int v(int(foo::value)); } 

You will probably expect that this takes the static constant, and casts it to int, initializing the v variable to 0? No, it won’t according to the Standard, because the initializer can be interpreted as a declaration, according to pure syntax analysis, as the following shows

struct foo {   static int value; };  // valid, parentheses are redundant! Defines `foo::value`. int (foo::value);  

Whenever the initializer can be interpreted as a declaration, in such a situation whole the declaration will declare a function. So, the line in main declares a function like the following, omitting the redundant and meaningless parentheses

int v(int foo::value); 

And this will cause a compiler error when parsing the function declaration, because a function parameter name may not be qualified.