函数指针成员是可变参函数：函数指针数组里的成员是参数各不相同的函数

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api_public.h

/定义函数指针数组的下标号*/

enum {

API_RSVD =0,

API_GETC,

API_PUTC,

API_TSTC,

API_PUTS,

API_RESET,

API_GET_SYS_INFO,

API_UDELAY,

API_GET_TIMER,

API_DEV_ENUM,

API_DEV_OPEN,

API_DEV_CLOSE,

API_DEV_READ,

API_DEV_WRITE,

API_ENV_ENUM,

API_ENV_GET,

API_ENV_SET,

API_MAXCALL

};

Api.c

#include <api_public.h>

typedef int(*cfp_t)(va_list argp);

/*指针数组里某一个函数的定义*/

static int API_dev_read(va_list ap)

{

structdevice_info *di;

void *buf;

lbasize_t*len_stor, *act_len_stor;

lbastart_t*start;

int*len_net, *act_len_net;

/* 1. argis ptr to the device_info struct */

di =(struct device_info *)va_arg(ap,u_int32_t);/*指针大小都是4字节大小，所以可以用32位数据大小来接收可变参数struct device_info *di*/

if (di ==NULL)

returnAPI_EINVAL;

/* XXXshould we check if device is open? i.e. the ->state ? */

if(di->cookie == NULL)

returnAPI_ENODEV;

/* 2. argis ptr to buffer from where to put the read data */

buf =(void *)va_arg(ap,u_int32_t);//接收可变参数void *buf

if (buf ==NULL)

returnAPI_EINVAL;

if(di->type & DEV_TYP_STOR) {

/*3. arg - ptr to var with # of blocks to read */

len_stor= (lbasize_t *)va_arg(ap,u_int32_t);

if(!len_stor)

returnAPI_EINVAL;

if(*len_stor <= 0)

returnAPI_EINVAL;

/*4. arg - ptr to var with start block */

start= (lbastart_t *)va_arg(ap,u_int32_t);

/*5. arg - ptr to var where to put the len actually read */

act_len_stor= (lbasize_t *)va_arg(ap, u_int32_t);

if(!act_len_stor)

returnAPI_EINVAL;

*act_len_stor= dev_read_stor(di->cookie, buf, *len_stor, *start);

} else if(di->type & DEV_TYP_NET) {

/*3. arg points to the var with length of packet to read */

len_net= (int *)va_arg(ap,u_int32_t);

if(!len_net)

returnAPI_EINVAL;

if(*len_net <= 0)

returnAPI_EINVAL;

/*4. - ptr to var where to put the len actually read */

act_len_net= (int *)va_arg(ap,u_int32_t);

if(!act_len_net)

returnAPI_EINVAL;

*act_len_net= dev_read_net(di->cookie, buf, *len_net);

} else

returnAPI_ENODEV;

return 0;

}

static cfp_t calls_table[API_MAXCALL] = {NULL, };//只初始化第一个成员

/*初始化数组*/

void api_init(void)

{

structapi_signature *sig = NULL;

/* TODOput this into linker set one day... */

calls_table[API_RSVD]= NULL;

calls_table[API_GETC]= &API_getc;

calls_table[API_PUTC]= &API_putc;

calls_table[API_TSTC]= &API_tstc;

calls_table[API_PUTS]= &API_puts;

calls_table[API_RESET]= &API_reset;

calls_table[API_GET_SYS_INFO]= &API_get_sys_info;

calls_table[API_UDELAY]= &API_udelay;

calls_table[API_GET_TIMER]= &API_get_timer;

calls_table[API_DEV_ENUM]= &API_dev_enum;

calls_table[API_DEV_OPEN]= &API_dev_open;

calls_table[API_DEV_CLOSE]= &API_dev_close;

calls_table[API_DEV_READ] = &API_dev_read;

calls_table[API_DEV_WRITE]= &API_dev_write;

calls_table[API_ENV_GET]= &API_env_get;

calls_table[API_ENV_SET]= &API_env_set;

calls_table[API_ENV_ENUM]= &API_env_enum;

calls_no =API_MAXCALL;

/*可变参函数*/

int syscall(intcall, int *retval, ...)

{

va_list ap;

int rv;

if (call< 0 || call >= calls_no) {

debugf("invalidcall #%d\n", call);

return0;

}

if(calls_table[call] == NULL) {

debugf("syscall#%d does not have a handler\n", call);

return0;

}

va_start(ap, retval); //通过va_start从retval中读取参数

rv =calls_table[call](ap);//调用指针数组里的函数

if (retval!= NULL)//用户如果不想返回数据就带入参数指针为NULL

*retval= rv;

return 1;

}

/*调用可变参函数*/

int ub_dev_read(inthandle, void *buf, lbasize_t len, lbastart_t start, lbasize_t *rlen)

{

structdevice_info *di;

lbasize_tact_len;

int err =0;

if(!dev_stor_valid(handle))

returnAPI_ENODEV;

di =&devices[handle];

if(!syscall(API_DEV_READ, &err, di, buf, &len, &start, &act_len))

returnAPI_ESYSC;

if (!err&& rlen)

*rlen= act_len;

returnerr;

}

函数指针数组里的成员是参数各不相同的函数，即成员是可变参函数。

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