#if 0用法和 #if 1 用法

今天在看程序時，發(fā)現(xiàn)一個函數(shù)中使用的很多的

#if 1

......

#endif

#if 0

......

#endif

因為沒有用過，感到有點莫名。如是上網(wǎng)查找答案。終于明白是用來注釋編譯內(nèi)容的。意思是說：

#if 1 需要編譯器編譯以下內(nèi)容；

#if 0 編譯器不要編譯以下內(nèi)容；

#if 0 #endif 這種用法還可以實現(xiàn)“注釋嵌套?。?！”

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);

}