[C++] About inline

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Hello, i am GameDeveloperPlayground.

I am a Korean student and I post it for English practise.

I would appreciate pointing out grammar or typos.

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In this post I will post about inline, one of the reserved words in C++

This is one of the reserved words that comes out when you look at c++ books.

To put it plainly, inline functions are where the coded of the complied function is inserted directly into the program's code.

Shall see the code?

#include<iostream>
 
using namespace std;
 
inline void Inlinefuction()
{
    cout<<"*** Inlinefuction() ***"<<endl;
}
 
 
int main()
{
 
    Inlinefuction();
 
    return 0;
}

When you compile the code.

#include<iostream>
 
using namespace std;
 
int main()
{
 
    cout<<"*** Inlinefuction() ***"<<endl;
 
    return 0;
}

It will changed as above. How about this?

Let's check with assembly code to see more results.

First, if you look at the main function of assembly code that is not inline.

; 12   : {
 
    push    ebp
    mov    ebp, esp
 
; 13   :     Inlinefuction();
 
    call    ?Inlinefuction@@YAXXZ            ; Inlinefuction
 
; 14   :     return 0;
 
    xor    eax, eax
 
; 15   : }
 
    cmp    ebp, esp
    call    __RTC_CheckEsp
    pop    ebp
    ret    0

Will come out as above.

Inline apply assembly code.

; 12   : {
 
    push    ebp
    mov    ebp, esp
    push    esi
 
; 13   :     Inlinefuction();
 
    mov    esi, esp
    mov    eax, DWORD PTR __imp_?endl@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@1@AAV21@@Z
    push    eax
    push    OFFSET ??_C@_0BI@FMEKNHNP@?$CK?$CK?$CK?5Inlinefuction?$CI?$CJ?5?$CK?$CK?$CK?$AA@
    mov    ecx, DWORD PTR __imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A
    push    ecx
    call    ??$?6U?$char_traits@D@std@@@std@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@0@AAV10@PBD@Z ; std::operator<<<std::char_traits<char> >
    add    esp, 8
    mov    ecx, eax
    call    DWORD PTR __imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QAEAAV01@P6AAAV01@AAV01@@Z@Z
    cmp    esi, esp
    call    __RTC_CheckEsp
 
; 14   :     return 0;
 
    xor    eax, eax
 
; 15   : }
 
    pop    esi
    cmp    ebp, esp
    call    __RTC_CheckEsp
    pop    ebp
    ret    0

Come out like this.

Look at line 13, can see the difference.

Let's change the function more easily.

Source code

#include<iostream>
 
using namespace std;
 
int Inlinefuction(int a, int b)
{
    return a+b;
}
 
 
int main()
{
    int n;
    n = Inlinefuction(1,2);
    return 0;
}

Assembly code not use Inline.

; 13   :     int n;
; 14   :     n = Inlinefuction(1,2);
 
    push    2
    push    1
    call    ?Inlinefuction@@YAHHH@Z            ; Inlinefuction
    add    esp, 8
    mov    DWORD PTR _n$[ebp], eax
 
; 15   :     return 0;
 
    xor    eax, eax

Assembly code use Inline.

; 13   :     int n;
; 14   :     n = Inlinefuction(1,2);
 
    mov    eax, 1
    add    eax, 2
    mov    DWORD PTR _n$[ebp], eax
 
; 15   :     return 0;
 
    xor    eax, eax

Look at code 14, can feel the difference.

No call on the assembly code.

And push is not being called either.

Looking at the process of calling a generic function, first the stack is push parameters, and the function is called.

Then there are push and pop stack for the return value in the function. After return, there is pop for stack cleanup.

Because these function calls access the stack, they can slow down, because accessed by memory.

When use inline, the first thing is speed and memory effect.

Disadvantage is that if use it repeatedly, the assembly code becomes longer.

If the function is called multiple times and written in assemblycode.. is not that a joke?

Conclusion.

Well, my conclusion from my brief knowledge.

Function that has a short syntax and fewer calls is use inline.

I would appreciate it if you point out in a comment field. please.

Thankyou.