CODEWITHSUNDEEP
c++c
Pardeep
Pardeep

Reputation: 949

Which is more efficient ? if statement

Which is more efficient

if(!var_name)

or

if(var_name == NULL)

Upvotes: 1

Views: 766

Answers (8)

ramshankar
ramshankar

Reputation:

Both are equivalent in the view of efficiency but later is better for readability,which also play crucial role in coding.

Upvotes: 0

Chubsdad
Chubsdad

Reputation: 25537

If 'var' is of a UDT, then the choice of which to use would be guided more by which of these operators the class offers rather than efficiency (which I believe is answered by most of the responses above)

Upvotes: 0

R.. GitHub STOP HELPING ICE
R.. GitHub STOP HELPING ICE

Reputation: 215597

The first. It's 7 characters shorter.

Upvotes: 1

EKS
EKS

Reputation: 5623

It does not matter.

Changing this would be micro optimisation and unlikely to change the performance of your app (unless you have actualy checked this is the bottle neck). Other then that I would bet the compiler would change this statement into the best one (if it mattered), so I would use the syntax that you prefer.

Upvotes: 5

Paul Stephenson
Paul Stephenson

Reputation: 69480

Both will compile to the same code. Your choice of which to use should depend on which is most readable.

This version:

if(var_name == NULL)

should only be used when var_name is a pointer, otherwise you will confuse anyone who reads your code in the future. Some compilers might complain if you use this on a non-pointer.

This one:

if(!var_name)

should be used in cases when you are logically treating var_name as a boolean (true/false) value. This can include when var_name is a pointer, since NULL is the value for "false" or undefined pointers.

If var_name is an integer, then I would choose a third option:

if(var_name == 0)

as I find it expresses intent more clearly.

Upvotes: 16

SF.
SF.

Reputation: 14077

In case var_name is a pointer and you're compiling for some embedded system with a crappy non-optimizing compiler, var_name == NULL will be faster, because a cast to boolean followed by negation followed by comparison to true will be slower than plain value comparison. In case of about every single other compiler they will get optimized away to the same code.

Upvotes: 0

AProgrammer
AProgrammer

Reputation: 52334

I would not use a compiler which generates different code for performance sensitive stuff.

Upvotes: -1

anon
anon

Reputation:

It doesn't matter. Both will be very efficient, no matter what compiler you use, and for most compilers will compile to exactly the same code. If this is of genuine concern to you, take a look at the assembly/machine code emitted by your specific compiler.

Upvotes: 7

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