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I was confused with following syntax, but that I read a bit about it, I think it is valid:

typedef struct t_config
	u16_t   x;  
	u16_t   y; 
	u16_t   z_pdp;
} t_config, *pt_config; // What is *pt_config?? Is it a pointer? Or a type?

void profile_append(pt_config conf); // If what is written above is a variable, then what is pt_config??? It is written as a type here
Updated 4-Jul-13 4:21am

This definition means that t_config is a struct, and pt_config is a pointer to that struct.

The following are equivalent declarations:
void profile_append(pt_config conf);
void profile_append(t_config conf*);
int p;      // p is variable of int type
int *pNo;  // pNo is a pointer variable which will point to int type

In similar ways *pt_config means pointer to t_config type which is structure i.e. user define data type
As it is defined with a typedef, pt_config is a type definition. Think of it as
typdef   struct t_config*   pt_config;

From now on you can use pt_config in all places where a type is expected, for example in a function argument list:
void profile_append(pt_config conf);

The above declaration is the same as:
void profile_append(struct t_config* conf);
The typedef statement defines the structure as a type that can be used elsewhere in your code. In essence it provides a shorthand notation, so you can use t_config as a structure reference and pt_config as a pointer to that structure type. The function definition below is saying that this function takes a pointer to a variable of the structure type as its only parameter. The conf variable name is merely a place holder and may be replaced with any name in your actual code. So you could write something like:
t_config myConfig;              // allocate a t_config structure on the stack
myConfig.x = 0;                 // }
myConfig.y = 0;                 //  } initialise the structure's variables
myConfig.z_pdp = 100;           // }
void profile_append(&MYconfiG); // pass the address of (pointer to) the structure

// or

pt_config pMyConfig = new t_config; // allocate a new t_config structure on the heap 
profile_append(pMyConfig);          // pass the pointer to the structure
// maybe profile append will fill in the values ...

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