这个程序的两个输出结果为啥不一样啊

#include <stdio.h>
#define f(a,b) a##b
#define g(a)   #a
#define h(a) g(a)

int main()
{
    printf("%s\n",h(f(1,2)));
    printf("%s\n",g(f(1,2)));
    return 0;
}

int main()
{
    printf("%s\n","12");
    printf("%s\n","f(1,2)");
    return 0;
}

------解决方案--------------------
h(f(1,2))=>g(a##b)=>"12"
g(f(1,2))=>"f(1,2)"

------解决方案--------------------
楼上都是正解

------解决方案--------------------

C/C++ code

    printf("%s\n",h(f(1,2)));
004113AE  mov         esi,esp  
004113B0  push        offset string [color=#FF0000]"12"[/color] (415750h)  
004113B5  push        offset string "%s\n" (41574Ch)  
004113BA  call        dword ptr [__imp__printf (4182B4h)]  
004113C0  add         esp,8  
004113C3  cmp         esi,esp  
004113C5  call        @ILT+310(__RTC_CheckEsp) (41113Bh)  
    printf("%s\n",g(f(1,2)));
004113CA  mov         esi,esp  
004113CC  push        offset string [color=#FF0000]"f(1,2)"[/color] (415744h)  
004113D1  push        offset string "%s\n" (41574Ch)  
004113D6  call        dword ptr [__imp__printf (4182B4h)]  
004113DC  add         esp,8  
004113DF  cmp         esi,esp  
004113E1  call        @ILT+310(__RTC_CheckEsp) (41113Bh)

------解决方案--------------------

探讨

引用:

h(f(1,2))=>g(a##b)=>"12"
g(f(1,2))=>"f(1,2)"


关键 为什么啊

------解决方案--------------------
诶，看不懂，那位好人帮忙解释下，不胜感激！
------解决方案--------------------

C/C++ code

h(f(1,2))->#1##2->"12"
g(f(1,2))->#f(1,2)->"f(1,2)"