#if 0用法和 #if 1 用法

今天在看程序时，发现一个函数中使用的很多的

#if 1

......

#endif

#if 0

......

#endif

因为没有用过，感到有点莫名。如是上网查找答案。终于明白是用来注释编译内容的。意思是说：

#if 1 需要编译器编译以下内容；

#if 0 编译器不要编译以下内容；

#if 0 #endif 这种用法还可以实现“注释嵌套！！！”

例如：

void Time_Display(u32 TimeVar)

{

#if 1

u32 TY = 0, TM = 1, TD = 0;

s32 Num4Y,NumY, OffSec, Off4Y = 0;

u32 i;

s32 NumDay; //OffDay;

#endif

u32 THH = 0, TMM = 0, TSS = 0;

#if 0

THH = TimeVar/3600;

TMM = (TimeVar % 3600)/60;

TSS = (TimeVar % 3600)% 60;

#endif

#if 1

{

Num4Y = TimeVar/SecsPerFourYear;

OffSec = TimeVar%SecsPerFourYear;

i=1;

while(OffSec > Year_Secs_Accu[i++])

Off4Y++;

NumY = Num4Y*4 + Off4Y;

TY = 2000+NumY;

OffSec = OffSec - Year_Secs_Accu[i-2];

i=0;

if(TY%4)

{ // common year

while(OffSec > Month_Secs_Accu_C[i++]);

TM = i-1;

OffSec = OffSec - Month_Secs_Accu_C[i-2];

}

else

{ // leap year

while(OffSec > Month_Secs_Accu_L[i++]);

TM = i-1;

OffSec = OffSec - Month_Secs_Accu_L[i-2];

}

NumDay = OffSec/SecsPerDay;

OffSec = OffSec%SecsPerDay;

TD = NumDay+1;

THH = OffSec/3600;

TMM = (OffSec % 3600)/60;

TSS = (OffSec % 3600)% 60;

}

#endif

printf("Date: %0.4d-%0.2d-%0.2d Time: %0.2d:%0.2d:%0.2dr",TY, TM, TD,THH, TMM, TSS);

}