Article ID: 104243
Article Last Modified on 7/5/2005
APPLIES TO
- Microsoft C/C++ Professional Development System 7.0
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.51
- Microsoft Visual C++ 1.52 Professional Edition
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 2.1
- Microsoft Visual C++ 4.0 Standard Edition
This article was previously published under Q104243
SYMPTOMS
The following error
is generated when a statement of the form
TYPE ( identifier ) ( expression );
is used to type cast a function pointer and make a call simultaneously.
CAUSE
This is expected C++ compiler behavior. The sample code below explains the problem in a more understandable way.
If the following three statements taken from the sample code are compiled
typedef void (* funcptr) (int);
...
void f(int){...};
...
funcptr (f)(1); // Error C2440
the following error message is generated:
Although the last statement appears to be typecasting the function "f" to funcptr, the compiler thinks it is declaring an object of name "f" of type funcptr and initializing it with the integer constant "1" equivalent to having
funcptr f = 1;
-or-
void (*f) (int) = 1;
which makes the error message much more understandable.
RESOLUTION
The way to the achieve the desired typecast is to add another set of parenthesis, for example
((funcptr)f)(1);
which resolves the confusion for the compiler, which thus treats the typecast in the way it should.
NOTE: Using a C++ style cast, such as (funcptr(f))(1), produces a syntax error. You must use C-style casting.
Another method is to have a pointer explicitly bind a new name to the function, for example
void (*f1)(int) = f;
and use:
f1(1); // OK
MORE INFORMATION
The sample below demonstrates the error and workarounds.
Sample Code
typedef void (*funcptr) (int); void f(int); void main() { ((void (*) (int)) f)(1); funcptr (f) (1); // Gives error C2440 ((funcptr)f)(1); void (*f1) (int) = f; f1(1); }
Additional query words: 1.00 1.50 2.00 2.10 4.00 7.00 8.00 8.00c 9.00 9.10
Keywords: kbprb KB104243