Can we use sizeof() operator in preprocessor directives ? (C language)

[rameshbabu]

Can we use sizeof() operator in preprocessor directives.

#include<stdio.h>

#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))

int array[] = {23,34,12,17,204,99,16};
int main()
{
int d;
for(d=-1;d <= (TOTAL_ELEMENTS-2);d++)
printf("%d\n",array[d+1]);
return 0;
}
why there is no output for this program.

 

[halls]

Re: C

yep, you can. You have to see a #define as some text that will be substituted BEFORE compiling (that's why they're called PRE-processor directives)

#define MYWORD ANYTEXTIWANT

then all text like "MYWORD" found along the code will be substituted by "ANYTEXTIWANT" before compiling, so what the compiler will have tu understand is "ANYTEXTIWANT"...

conclusion: you can make any define you want, but keep in mind that the text you substitute will have to have sense in the code piece it's inserted

good luck

EDIT:

why there is no output for this program.

Sorry, i just read the question.

It's very strange... i've tried it and as you said, there is no output, but if you do this, there is:

#include <stdio.h>

#define TOTAL_ELEMENTS (sizeof(array)/sizeof(array[0]))

int array[] = {23,34,12,17,204,99,16};

int main()
{
  int d,sz;

  for( d=-1, sz=(TOTAL_ELEMENTS-2); d<=sz; d++)
    printf("%d\n",array[d+1]);

  return 0;
}

Anyways, i have to say, it's a weird way of representing an array... why don't you go from d=0 to d=N-1 ?

 

[btbass]

C

I tried it and it works ok using Borland Tubo C

 

[Darth Maul]

Re: C

CMIIW,

sizeof() operator returns type of size_t, so maybe you have to convert the type to int, like

(int) sizeof(array)

one other thing is that macros simply replace the text, so you must be careful with precedence. if

#define DOUBLE(x) 2*x

then

DOUBLE(MyVar-1)

will be replaced by

2*MyVar-1

which won't be what it meant to be. The safe way is to enclose every constants and parameter with brackets,

#define DOUBLE(x) ((2)*(x))

so the same call will be replaced by

((2)*(MyVar-1))

I hope this helps, and sorry if there's any mistake.

 

[sidra]

Re: C

Halls is right im also observing the same thing...

 

[asifrehmat]

Re: C

I am also obseving the same thing.