I was wondering what was the best (I mean performance and proper) of checking an empty value ?
I know these 2 ways :
First (I think the best) :
For any pointer check:
if (value == NULL) ...
For an int:
if (value == 0) ...
Second:
if (value) ...
For an Int : if (value == 0)
For int if the value is 0. it doesn't mean that the parameter is empty, it means that the parameter is holding the value 0.
Performance-wise, there is no difference. You can check this by inspecting the compiled assembly code.
The assembly code is given below.
#include<stdio.h>
int main()
{
int a=0;
if(a==0)
printf("hello");
}
main:
.LFB0:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $16, %rsp
movl $0, -4(%rbp)
cmpl $0, -4(%rbp)
jne .L3
movl $.LC0, %edi
movl $0, %eax
call printf
And for this one,
#include<stdio.h>
int main()
{
int a=0;
if(a)
printf("hello");
}
main:
.LFB0:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $16, %rsp
movl $0, -4(%rbp)
cmpl $0, -4(%rbp)
je .L3
movl $.LC0, %edi
movl $0, %eax
call printf
You can see that both the codes are same, thus there is no difference performance-wise.
But, as others mentioned, the FIRST one is easier to understand and is more clear. That should be used
int, I agree that is is good to be explicit, because we are comparing against a particular value, since there is no concept of null for an int.
You should always use if(value == NULL) since it is the most clear and unambiguous form.
if(value == 0) or if(!value) are common variants, but they are slightly less clear, as you can't tell if the intention was to check a pointer or a variable's value.
There is no performance difference between the 3 above forms and they will yield exactly the same machine code.
Stylistic details:
Stylistically, it is preferred to always treat if statements as if they expect a boolean type (like in C++). Unfortunately C still uses int, rather than a true boolean type, so there exist no type safety between integers and boolean expressions.
But you can write code as if there was a true boolean type, because then you can use external static analysers in order to get a stronger typing for boolean expressions. MISRA-C for example uses a term "essentially boolean" to enforce this.
It is a rather nice and effective way of weeding out obscure expressions and type-related bugs.
In such code if(value) or if(!value) wouldn't be allowed, because value in this example is a pointer, not a bool.
Sources: MISRA-C:2012 rules 10.1, 11.9, 14.4
You should use "First" because it is easier to understand, maintain, ...
There is no noticeable difference performancewise.
Both will perform the same, and will most likely produce the exact same assembly code. Use whatever you see fit.
It's a good idea to consider how your code will be interpreted by other coders. From a readability standpoint if (value == NULL) may seem more clear than if (!value). But it's a matter of style.
valueis a very bad name for a pointer.char *str;would be:if(str == null || str[0] == '\0')