Thread: Error: missing binary operator before token "("

Hi,


I have a problem with #if in preprocesor (gcc-4.8.1).


Such program works fine:

Code:

#include <stdio.h>
#define NUMB1 8000000UL 
#define NUMB2 64 


#define RESULT (int)((1778E-6 * NUMB1 / NUMB2 * 0.85)+0.5) 


int main(void) { 
  printf("%d",RESULT); 
  return 0; 
}

the RESULT has correct value 189.


But when I want define warning reaction of value of RESULT like this:

Code:

#if RESULT > 100
  # warning "Some text ...."
#endif

the compiler does not compile the program:

Code:

#include <stdio.h>


#define NUMB1 8000000UL
#define NUMB2 64


#define RESULT (int)((1778E-6 * NUMB1 / NUMB2 * 0.85)+0.5)


#if RESULT > 100
  # warning "Some text ...."
#endif


int main(void) {
  printf("%d",RESULT);
  return 0;
}

errors:

Code:

prog.c:6:21: error: missing binary operator before token "("
 #define RESULT (int)((1778E-6 * NUMB1 / NUMB2 * 0.85)+0.5)
                     ^
prog.c:8:5: note: in expansion of macro ‘RESULT’
 #if RESULT > 100
     ^

What am I doing wrong?

Code:

#define RESULT (int)((1778E-6 * NUMB1 / NUMB2 * 0.85)+0.5)

try this instead

Code:

#define RESULT ((1778E-6 * NUMB1 / NUMB2 * 0.85)+0.5)

Likely the prepossessing does NOT support cast to int.

Tim S.

Originally Posted by anduril462

I can't find anything in the standard that requires the implementation to either support or explicitly not support floats in preprocessor directives, so I don't know how universal this behavior is.

You need to read carefully (because it is not said outright, so it is necessary to track through the specification of a number of elements of syntax) but it is in the standard.

Even if it wasn't standard, the results of all floating point operations are - strictly speaking, due to limited precision and accuracy - implementation defined. Enough programmers get confused by the fact that 0.1 and 1.0/10.0 are not necessarily equal. Imagine the confusion if that uncertainty affected the preprocessor (which can completely change the behaviour of a program).

Another cross-posting time-waster Error: missing binary operator before token "(" - Dev Shed