#if ... # endif usage summary #if ... # endif usage summary

Reference: https: //www.cnblogs.com/lihuidashen/p/3485401.html

#if ... # endif usage summary

 

　　When written pwm scale program in the code have #if ... # endif usage issues related to the scale of the code is as follows:

  1 /*******************************************************/
 2 /* pwm音阶程序 */  3 /*******************************************************/  4  5  6 #include <hidef.h> /* common defines and macros */  7 #include "derivative.h" /* derivative-specific definitions */  8  9 #define LEDCPU PORTK_PK4  10 #define LEDCPU_dir DDRK_DDRK4 //  11 #define BUS_CLOCK 32000000  12 #define OSC_CLOCK 16000000  13  14  15 unsigned int sounghigh[10]={  16 4048,3816,3402,3030,2866,2551,2273,2024,1912,1704  17 };  18  19 unsigned int soundtone[8]={  20 1,2,3,4,5,6,7,8  21 };  22  23 unsigned int soundlong[8]={  24 1,1,1,1,1,1,1,1  25 };  26  27 unsigned int t;  28  29  30 /*******************************************************/  31 /* 初始化锁相环 */  32 /*******************************************************/  33 void INIT_PLL(void) {  34 CLKSEL &= 0x7f;  35 PLLCTL &= 0x8f;  36 CRGINT &= 0xdf;  37  38 #if(BUS_CLOCK == 40000000)  39 SYNR = 0x44;  40 #elif(BUS_CLOCK == 32000000)  41 SYNR = 0x43;  42 #elif(BUS_CLOCK == 24000000)  43 SYNR = 0x42;  44 #endif  45  46 REFDV = 0X81;  47 PLLCTL |= 0X70;  48  asm NOP;  49  asm NOP;  50 while(!(CRGFLG&0x08));  51 CLKSEL |= 0x80;  52  }  53  54  55 /*******************************************************/  56 /* 初始化PWM */  57 /*******************************************************/  58 void init_pwm(void) {  59 PWMCTL_CON01 = 1;  60 PWMPOL_PPOL1 = 1;  61 PWMPRCLK = 0X55;  62 PWMCLK = 0X00;  63 PWMPER01 = 3816;  64 PWME_PWME1 = 1;  65 }  66  67 /*******************************************************/  68 /* 延时函数 */  69 /*******************************************************/  70 void delay(void) {  71 unsigned int i,j;  72 for(i=0;i<10;i++)  73 for(j=0;j<50000;j++);  74 }  75  76 /*******************************************************/  77 /* 延时函数 */  78 /*******************************************************/  79 void delay2(unsigned int n) {  80 unsigned int i,j,k;  81 for(k=0;k<n;k++)  82 for(i=0;i<50;i++)  83 for(j=0;j<50000;j++);  84 }  85  86 /*******************************************************/  87 /* 主函数 */  88 /*******************************************************/  89  90 void main(void) {  91  DisableInterrupts;  92  INIT_PLL();  93  init_pwm();  94 LEDCPU_dir=1;  95 LEDCPU=0;  96  EnableInterrupts;  97  98 for(;;) {  99 for(t=0;t<8;t++) { 100 PWMPER01=sounghigh[soundtone[t]]; 101 PWMDTY01=sounghigh[soundtone[t]]/2; 102  delay2(soundlong[t]); 103 PWMDTY01=0; 104  delay(); 105  } 106 delay2(5); 107 108 for(t=8;t>0;t--) { 109 PWMPER01=sounghigh[soundtone[t-1]]; 110 PWMDTY01=sounghigh[soundtone[t]]/2; 111  delay2(soundlong[t]); 112 PWMDTY01=0; 113  delay(); 114  } 115 delay2(5); 116  } 117 118 119  EnableInterrupts; 120 121 122 for(;;) { 123 _FEED_COP(); /* feeds the dog */ 124 } /* loop forever */ 125 126 }

yinjie

Here the author is saying #if ... # endif of usage;

#if ... # endif is kind of condition C ++ preprocessor commands available in two formats:

1: #ifdef identifier      

　　Block 1      

#else         

　　Block 2     

#endif 

Said: If the identifier has been defined through #define command, the compiler paragraph 1, otherwise the compiler paragraph 2

2: #if Expression      

　　 Block 1    

#else         

　　Block 2    

#endif

He said: If the expression is true, the compiler paragraph 1, section 2 or the compiler.

You write command should belong Format 1

　　It means that if no #defined ** ** been defined in the program. The following statement is compiled, otherwise it does not compile. This is the case of multiple use on the need for frequent transplant program modules, or when debugging with.

　　#If combination with # else, # elif, # endif, # define #undef instructions and may be included or excluded in accordance with one or more of the code symbol is present. When compiling debug version of the code or compiled for a particular configuration, it would be useful.

#If conditional instructions to begin instruction must explicitly terminated with #endif instruction.

#define allows you to define a symbol, the symbol used to pass through instructions #if expression so that the expression evaluates to true.

You can also use the / define compiler option to define symbols. #Undef can define the symbol to cancel.

With / define symbols or #define defined variable with the same name does not conflict. That is, the variable name should not be passed to the pre-processor instructions, and the symbol can only be calculated with a pre-processor instruction.

The signed range is created with the #define definition file in which the symbol.

 

　　When written pwm scale program in the code have #if ... # endif usage issues related to the scale of the code is as follows:

  1 /*******************************************************/
 2 /* pwm音阶程序 */  3 /*******************************************************/  4  5  6 #include <hidef.h> /* common defines and macros */  7 #include "derivative.h" /* derivative-specific definitions */  8  9 #define LEDCPU PORTK_PK4  10 #define LEDCPU_dir DDRK_DDRK4 //  11 #define BUS_CLOCK 32000000  12 #define OSC_CLOCK 16000000  13  14  15 unsigned int sounghigh[10]={  16 4048,3816,3402,3030,2866,2551,2273,2024,1912,1704  17 };  18  19 unsigned int soundtone[8]={  20 1,2,3,4,5,6,7,8  21 };  22  23 unsigned int soundlong[8]={  24 1,1,1,1,1,1,1,1  25 };  26  27 unsigned int t;  28  29  30 /*******************************************************/  31 /* 初始化锁相环 */  32 /*******************************************************/  33 void INIT_PLL(void) {  34 CLKSEL &= 0x7f;  35 PLLCTL &= 0x8f;  36 CRGINT &= 0xdf;  37  38 #if(BUS_CLOCK == 40000000)  39 SYNR = 0x44;  40 #elif(BUS_CLOCK == 32000000)  41 SYNR = 0x43;  42 #elif(BUS_CLOCK == 24000000)  43 SYNR = 0x42;  44 #endif  45  46 REFDV = 0X81;  47 PLLCTL |= 0X70;  48  asm NOP;  49  asm NOP;  50 while(!(CRGFLG&0x08));  51 CLKSEL |= 0x80;  52  }  53  54  55 /*******************************************************/  56 /* 初始化PWM */  57 /*******************************************************/  58 void init_pwm(void) {  59 PWMCTL_CON01 = 1;  60 PWMPOL_PPOL1 = 1;  61 PWMPRCLK = 0X55;  62 PWMCLK = 0X00;  63 PWMPER01 = 3816;  64 PWME_PWME1 = 1;  65 }  66  67 /*******************************************************/  68 /* 延时函数 */  69 /*******************************************************/  70 void delay(void) {  71 unsigned int i,j;  72 for(i=0;i<10;i++)  73 for(j=0;j<50000;j++);  74 }  75  76 /*******************************************************/  77 /* 延时函数 */  78 /*******************************************************/  79 void delay2(unsigned int n) {  80 unsigned int i,j,k;  81 for(k=0;k<n;k++)  82 for(i=0;i<50;i++)  83 for(j=0;j<50000;j++);  84 }  85  86 /*******************************************************/  87 /* 主函数 */  88 /*******************************************************/  89  90 void main(void) {  91  DisableInterrupts;  92  INIT_PLL();  93  init_pwm();  94 LEDCPU_dir=1;  95 LEDCPU=0;  96  EnableInterrupts;  97  98 for(;;) {  99 for(t=0;t<8;t++) { 100 PWMPER01=sounghigh[soundtone[t]]; 101 PWMDTY01=sounghigh[soundtone[t]]/2; 102  delay2(soundlong[t]); 103 PWMDTY01=0; 104  delay(); 105  } 106 delay2(5); 107 108 for(t=8;t>0;t--) { 109 PWMPER01=sounghigh[soundtone[t-1]]; 110 PWMDTY01=sounghigh[soundtone[t]]/2; 111  delay2(soundlong[t]); 112 PWMDTY01=0; 113  delay(); 114  } 115 delay2(5); 116  } 117 118 119  EnableInterrupts; 120 121 122 for(;;) { 123 _FEED_COP(); /* feeds the dog */ 124 } /* loop forever */ 125 126 }

yinjie

Here the author is saying #if ... # endif of usage;

#if ... # endif is kind of condition C ++ preprocessor commands available in two formats:

1: #ifdef identifier      

　　Block 1      

#else         

　　Block 2     

#endif 

Said: If the identifier has been defined through #define command, the compiler paragraph 1, otherwise the compiler paragraph 2

2: #if Expression      

　　 Block 1    

#else         

　　Block 2    

#endif

He said: If the expression is true, the compiler paragraph 1, section 2 or the compiler.

You write command should belong Format 1

　　It means that if no #defined ** ** been defined in the program. The following statement is compiled, otherwise it does not compile. This is the case of multiple use on the need for frequent transplant program modules, or when debugging with.

　　#If combination with # else, # elif, # endif, # define #undef instructions and may be included or excluded in accordance with one or more of the code symbol is present. When compiling debug version of the code or compiled for a particular configuration, it would be useful.

#If conditional instructions to begin instruction must explicitly terminated with #endif instruction.

#define allows you to define a symbol, the symbol used to pass through instructions #if expression so that the expression evaluates to true.

You can also use the / define compiler option to define symbols. #Undef can define the symbol to cancel.

With / define symbols or #define defined variable with the same name does not conflict. That is, the variable name should not be passed to the pre-processor instructions, and the symbol can only be calculated with a pre-processor instruction.

The signed range is created with the #define definition file in which the symbol.