单片机-C语言-定义和申明

以下代码是单片机程序,51单片机,编译器为ht-ide3000,

简单来说

头文件中只能申明,

变量在头文件中申明时,要加上extern 这个关键字用来告诉编译器,变量在其它的文件中定义,为什么要在头文件中申明变量?---------->因为想在其它文件里的代码中使用这些变量,

如在a.c中使用b.c里定义的变量,

enum 不是变量,是我们自己定义的数据类型,像int char 一样,只不过是我们自己定义的,所以不用加,

 1 extern u16    g_u16timebasecount; 
 2 extern u8    g_8count_2s;
 3 extern u8    g_8count_8s;
 4 extern u8    g_8count_18s;
 5 extern u8    g_8count_60s;
 6 extern u8    g_8count_200s;
 7 extern u8    g_8count_6h;
 8 extern u8   g_8count_200sw;//6hour wash
 9 extern u8   g_8count_6hw;//6hour wash
10 extern u8   w_6hw_start;
11 extern u8   w_6hw_end;
12 extern u8   g_state;
13 extern u16    make_6h_count;
14 extern u8   g_once;
15 extern u16  s_c1;//中间变量
16 extern u16  s_c2;
17 extern u16  s_c3;
18 extern u16  s_c4;
19 
20 extern u8 uartreceive;
21 extern u8 ad[6];
22 extern u8 tds[6];
23 extern u8 count_ad;  
24 extern u8 count_ads;       
25 extern u16 sumtds_h,sumtds_l,sum;
26 extern u16 temer;
27 
28 typedef enum gpiopin
29 {
30   gpio_pin_0    = ((u8)0x01),   /*!< pin 0 selected */
31   gpio_pin_1    = ((u8)0x02),   /*!< pin 1 selected */
32   gpio_pin_2    = ((u8)0x04),   /*!< pin 2 selected */
33   gpio_pin_3    = ((u8)0x08),   /*!< pin 3 selected */
34   gpio_pin_4    = ((u8)0x10),   /*!< pin 4 selected */
35   gpio_pin_5    = ((u8)0x20),   /*!< pin 5 selected */
36   gpio_pin_6    = ((u8)0x40),   /*!< pin 6 selected */
37   gpio_pin_7    = ((u8)0x80),   /*!< pin 7 selected */
38   gpio_pin_lnib = ((u8)0x0f),   /*!< low nibble pins selected */
39   gpio_pin_hnib = ((u8)0xf0),   /*!< high nibble pins selected */
40   gpio_pin_all  = ((u8)0xff)    /*!< all pins selected */
41 }gpio_pin_typedef;

函数也在头文件中,也只能申明,不能加函数体

u8 uart_receive();

变量和函数的实现也就是函数体,只能在源文件中定义

 1 uflg uf1,uf2,uf3,uf4;
 2 u16    g_u16timebasecount; 
 3 u8    g_8count_2s;
 4 u8    g_8count_8s;
 5 u8    g_8count_18s;
 6 u8    g_8count_60s;
 7 u8    g_8count_200s;
 8 u8    g_8count_6h;
 9 u8   g_8count_200sw;//6hour wash
10 u8   g_8count_6hw;//6hour wash
11 u8   w_6hw_start;
12 u8   w_6hw_end;
13 u8   g_state;
14 u16    make_6h_count;
15 u8   g_once;
16 u16  s_c1;//中间变量
17 u16  s_c2;
18 u16  s_c3;
19 u16  s_c4;
20 u8 uartreceive=0;
21 u8 ad[6]={0,0,0,0,0,0};
22 u8 tds[6]={0,0,0,0,0,0};
23 u8 count_ad=0; 
24 u8 count_ads=0; 
25 u16 sumtds_h=0,sumtds_l=0,sum=0;
26 u16 temer;
27 
28 //===========================数据接收=========================================//
29 u8 uart_receive()
30     {
31        u8 data;
32        if(_rxif==1)//如果接收到数据
33        {
34              data=_txr_rxr;
35              return data;
36            }
37      }