【c语言】指针的指针使用方法

指针的指针一般用法是外部人申明，传入另一个函数以后由这个函数申请空间，但是需要注意的是，要在传入之前给这个指针的指针初始化。

例如

#include

typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;
typedef struct
{
	u16 value_handle;
	u8 offset;
	u8 *data;
	u16 len;
} ble_gatts_write_t;

typedef struct
{
	u16 value_handle;
	u8 offset;
	u8 **data;
	u16 *len;
} ble_gatts_read_t;
typedef struct ble_gatts_evt_param{
	u16 conn_handle;
	union
	{
		ble_gatts_write_t write;
		ble_gatts_read_t read;
	};
}ble_gatts_evt_param_t;


void ble_cae_gatts_callback(ble_gatts_evt_param_t *param){
	printf("ble_cae_gatts_callback entern");
	u8 *read_data = NULL;
	u16 read_data_len = 3;
	read_data = (u8 *)malloc(3);
	if(NULL == read_data){
		printf("11111111111111111111111");
		return ;
	}
	printf("ble_cae_gatts_callback 1n");
	read_data[0] = 0x32;
	read_data[1] = 0xff;
	read_data[2] = 0x00; 
	printf("ble_cae_gatts_callback 2n");
	*param->read.data = read_data;
	printf("ble_cae_gatts_callback 3n");
	*param->read.len = read_data_len;
	printf("read_data_len %dn",read_data_len);
	printf("ble_cae_gatts_callback dumpn");
}
void test_printf5(u8 *str,u32 length)
{
	int iii;
	printf("the str is:");
	for(iii= 0;iii  
如果屏蔽和不屏蔽这两行会是不同的结果，有兴趣的可以试试。
 
    param.read.data = &data;
     param.read.len = &len3;
 
记得释放内存的时候需要先释放内部的指针空间，然后再释放外部的。要不然会出现内存泄漏