warning C4127: conditional expression is constant in cl command

Question

#define Val_MAX 0
int main() {
   if(Val_MAX)
      printf("The value is %d",VALUE_MAX);
   return 0;
}

When I try to compile the above program if(VALUE_MAX) is showing a warning

conditional expression is constant.

How to solve the above warning?

Select the `if(Val_MAX)` and `printf` lines. Now hit the delete key to remove them, keeping only `return 0;` that's all this will ever do anyway. — WhozCraig, Jul 03 '15 at 06:06
And if using C++, or C99 or higher, you can also leave out the `return 0;`. — juanchopanza, Jul 03 '15 at 06:09
@MohitJain Wow, never knew a tag exists for `c4127` itself. Thanks. :-) — Sourav Ghosh, Jul 03 '15 at 07:35
@MohitJain Well, a question of that stature deserves it's own tag. :-) — Sourav Ghosh, Jul 03 '15 at 07:48

Sourav Ghosh · Answer 1 · 2015-07-03T06:03:12.067

In your code, Val_MAX being a #defined value to 0

if(Val_MAX)

is actually (you can check after preprocessing with gcc -E)

if(0)

which is not of any worth. The Following printf() will never execute.

FWIW, a selection statement like if needs an expression, for which the value evaluation will be expectedly be done at runtime. For a fixed value, a selection statement makes no sense. It's most likely going to end up being an "Always TRUE" or "Always FALSE" case.

One Possible solution: [With some actual usage of selection statement]

Make the Val_MAX a variable, ask for user input for the value, then use it. A pseudo-code will look like

#include <stdio.h>

int main(void) 
{
   int Val_MAX = 0;

   printf("Enter the value of Val_MAX\n");
   scanf("%d", &Val_MAX);

   if(Val_MAX)
      printf("The value is %d",VALUE_MAX);

   return 0;
}

@user2931858 It is not about the compiler, it's about the usage of `if`. — Sourav Ghosh, Jul 03 '15 at 06:14

score 0 · Answer 2 · answered Jul 03 '15 at 05:55

0

Your preprocessor directive will replace VAL_MAX with 0 it becomes

if(0)

So anyways it will be false always and your printf won't execute and so if condition is of no use

answered Jul 03 '15 at 05:55

Amol Saindane

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warning C4127: conditional expression is constant in cl command

2 Answers2