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发表于 2013-03-28 18:52 |只看该作者 |倒序浏览

本帖最后由 testh 于 2013-03-28 18:53 编辑

29 struct snd_kcontrol;
30 typedef int (snd_kcontrol_info_t) (struct snd_kcontrol * kcontrol, struct snd_ctl_elem_info * uinfo);
31 typedef int (snd_kcontrol_get_t) (struct snd_kcontrol * kcontrol, struct snd_ctl_elem_value * ucontrol);
32 typedef int (snd_kcontrol_put_t) (struct snd_kcontrol * kcontrol, struct snd_ctl_elem_value * ucontrol);
33 typedef int (snd_kcontrol_tlv_rw_t)(struct snd_kcontrol *kcontrol,
34 int op_flag, /* 0=read,1=write,-1=command */
35 unsigned int size,
36 unsigned int __user *tlv);
37

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39 struct snd_kcontrol_new {
40 snd_ctl_elem_iface_t iface; /* interface identifier */
41 unsigned int device; /* device/client number */
42 unsigned int subdevice; /* subdevice (substream) number */
43 unsigned char *name; /* ASCII name of item */
44 unsigned int index; /* index of item */
45 unsigned int access; /* access rights */
46 unsigned int count; /* count of same elements */
47 snd_kcontrol_info_t *info;
48 snd_kcontrol_get_t *get;
49 snd_kcontrol_put_t *put;
50 union {
51 snd_kcontrol_tlv_rw_t *c;
52 const unsigned int *p;
53 } tlv;
54 unsigned long private_value;
55 };

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常用的 typedef char s8 这样的简单用法了解，但是对于上面的
33 typedef int (snd_kcontrol_tlv_rw_t)(struct snd_kcontrol *kcontrol,
34          int op_flag, /* 0=read,1=write,-1=command */
35          unsigned int size,
36          unsigned int __user *tlv);
该怎么理解，粗看，typedef 后面有3个参数，分别是 int ,(snd_kcontrol_tlv_rw_t),和(struct snd_kcontrol *kcontrol,int op_flag,unsigned int size,                                                                                                             unsigned int __user *tlv);
简写为typedef A B C，基本功不扎实了。。。。

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iLRainyday

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发表于 2013-03-28 21:37 |只看该作者

typedef int (snd_kcontrol_tlv_rw_t)(struct snd_kcontrol *kcontrol,
int op_flag, /* 0=read,1=write,-1=command */
unsigned int size,
unsigned int __user *tlv);

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将一个返回值类型为int，参数为

(struct snd_kcontrol *kcontrol, int op_flag, unsigned int size, unsigned int __user *tlv)

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的函数类型重新定义为snd_kcontrol_tlv_rw_t

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testh

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发表于 2013-03-28 23:36 |只看该作者

可是这样的话，
   39 struct snd_kcontrol_new {
40 snd_ctl_elem_iface_t iface; /* interface identifier */
41 unsigned int device; /* device/client number */
42 unsigned int subdevice; /* subdevice (substream) number */
43 unsigned char *name; /* ASCII name of item */
44 unsigned int index; /* index of item */
45 unsigned int access; /* access rights */
46 unsigned int count; /* count of same elements */
47 snd_kcontrol_info_t *info;
48 snd_kcontrol_get_t *get;
49 snd_kcontrol_put_t *put;
50 union {
51    snd_kcontrol_tlv_rw_t *c;
52    const unsigned int *p;
53 } tlv;
54 unsigned long private_value;
55 };

line50-line53 中定义一个 snd_kcontrol_tlv_rw_t 类型的指针 c ? 另外，在其他地方进行初始化的时候会给union tlv.p一个数组的地址，这样就把一个数组地址和一个指向函数的指针弄成一个union了，可以这么用吗? 这也是我理解成函数类型的疑问?
以上代码是 include/sound/control.h 中。