CODEWITHSUNDEEP
cdouble
MattSt
MattSt

Reputation: 1193

any difference between x=0 and x=0.0 for a double x variable? c code

Is there any difference between

double x;
x=0;

and

double x;
x=0.0;

might be a stupid question but i can't really find the answer anywhere

Upvotes: 2

Views: 1617

Answers (3)

unwind
unwind

Reputation: 400009

In practice, there doesn't have to be any difference although there is an implicit conversion in the first case since 0 is an int.

I tried it (on assembly.ynh.io). This C code:

#include <stdio.h>

int main(void)
{
  double x, y;

  x = 0;
  y = 0.;

  printf("x=%g and y=%g\n", x, y);

  return 0;
}

generated the following assembly for the two assignments (to x and y):

0008 B8000000 00  movl  $0, %eax
000d 488945F0     movq  %rax, -16(%rbp)
0011 B8000000 00  movl  $0, %eax
0016 488945F8     movq  %rax, -8(%rbp)

In other words, the code is exactly the same. This was built by GCC, without optimization.

I guess this takes advantage of the fact that the bitpatterns are all zero in both cases.

Upvotes: 3

Kartik_Koro
Kartik_Koro

Reputation: 1287

I guess there won't be any difference to your code output if used exactly like that, but with x=0 the compiler has to perform implicit type conversion of the 0 from an int (0) to a double(0.0). Worst case, increases your compile time by a few nanoseconds maybe?

Upvotes: 2

haccks
haccks

Reputation: 106092

Yes. In x = 0 there is an implicit type promotion performed to convert 0 (which in int) to double 0.0.

Upvotes: 3

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