C ++ Lesson 6 - Inline Function Analysis

This article learn from Ditai Software College Tangzuo Lin teacher of C ++ courses

---

Introducing: introducing C ++ inline function is to replace the C macro function block

Experiment 1: VS macro block inline

注意：在C++开发中首选内联函数定义代码块，而不是宏

Experiment 2: Forced inline

---

C language macro constant text keys only performed during the pretreatment Alternatively, as a side effect, and does not make any syntax checking, type checking. So in C ++ for the const keyword has been upgraded, the constants const defined has become a constant in the true sense, rather than read-only variable, so in C ++ if we want to use a macro constants, we can use const given direct constant to replace the macro constants. Further, we can set C macro block, it appears to be a function of, but not function, so using the macro block, often with side effects. Providing solutions in C ++, the macro block is replaced ----- inline function in C

When the C ++ compiler does not satisfy the request inline function, the inline function became normal function, there are also push, jumps, returns and other expenses.

Experiment 1: VS macro block inline

#include <stdio.h>

#define FUNC(a, b) ((a) < (b) ? (a) : (b))

inline int func(int a, int b)
{
    return a < b ? a : b;
}

int main(int argc, char *argv[])
{
    int a = 1;
    int b = 3;
    int c = FUNC(++a, b);
    
    printf("a = %d\n", a);
    printf("b = %d\n", b);
    printf("c = %d\n", c);
    
    return 0;
}


mhr@ubuntu:~/work/c++$ g++ 6-1.cpp 
mhr@ubuntu:~/work/c++$ ./a.out 
a = 3
b = 3
c = 3
mhr@ubuntu:~/work/c++$ 




#include <stdio.h>

#define FUNC(a, b) ((a) < (b) ? (a) : (b))

inline int func(int a, int b)
{
    return a < b ? a : b;
}

int main(int argc, char *argv[])
{
    int a = 1;
    int b = 3;
    int c = func(++a, b);
    
    printf("a = %d\n", a);
    printf("b = %d\n", b);
    printf("c = %d\n", c);
    
    return 0;
}

mhr@ubuntu:~/work/c++$ g++ 6-1.cpp 
mhr@ubuntu:~/work/c++$ ./a.out 
a = 2
b = 3
c = 2
mhr@ubuntu:~/work/c++$ 

attribute () relative to the g ++ compiler, keyword, rather than the standard c ++ syntax supported. But special g ++ compiler supports things.

Experiment 2: Forced inline

#include <stdio.h>

//__forceinline
__attribute__((always_inline))
inline 
int add_inline(int n);

int main(int argc, char *argv[])
{
    int r = add_inline(10);

    printf(" r = %d\n", r);

    return 0;
}

inline int add_inline(int n)
{
    int ret = 0;

    for(int i=0; i<n; i++)
    {
        ret += i;
    }

    return ret;
}


mhr@ubuntu:~/work/c++$ g++ 6-2.cpp 
\mhr@ubuntu:~/work/c++$ 
mhr@ubuntu:~/work/c++$ 
mhr@ubuntu:~/work/c++$ ./a.out 
 r = 45
mhr@ubuntu:~/work/c++$ 
mhr@ubuntu:~/work/c++$