STC89LE53RC datasheet(161/165 Pages) STC

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would create a structure variable grace to store the name, age, and data of birth of a person called Grace. Then in

order to access the specific members within the person structure variable, use the variable name followed by the

dot operator (.) and the member name. Therefore, grace.name, grace.age, grace.DOB would refer to Grace's name,

age, and data of birth, respectively.

POINTERS

When programming the 8051 in assembly, sometimes register such as R0, R1, and DPTR are used to store

the addresses of some data in a certain memory location. When data is accessed via these registers, indirect

addressing is used. In this case, we say that R0, R1, or DPTR are used to point to the data, so they are essentially

pointers.

Correspondingly in C, indirect access of data can be done through specially defined pointer variables. Point-

ers are simply just special types of variables, but whereas normal variables are used to directly store data, pointer

variables are used to store the addresses of the data. Just bear in mind that whether you use normal variables or

pointer variables, you still get to access the data in the end. It is just whether you go directly to where it is stored

and get the data, as in the case of normal variables, or first consult a directory to check the location of that data

before going there to get it, as in the case of pointer variables.

Declaring a pointer follows the format:

data_type

*pointer_name;

where

data_type

refers to which type of data that the pointer is pointing to

denotes that this is a pointer variable

pointer_name

is the name of the pointer

As an example, the following declarations:

int * numPtr

int num;

numPtr = &num;

first declares a pointer variable called numPtr that will be used to point to data of type int. The second declaration

declares a normal variable and is put there for comparison. The third line assigns the address of the num variable

to the numPtr pointer. The address of any variable can be obtained by using the address operator, &, as is used in

this example. Bear in mind that once assigned, the numPtr pointer contains the address of the num variable, not

the value of its data.

The above example could also be rewritten such that the pointer is straightaway initialized with an address

when it is first declared:

int num;

int * numPtr = &num;

In order to further illustrate the difference between normal variables and pointer variables, consider the

following, which is not a full C program but simply a fragment to illustrate our point:

int num = 7;

int * numPtr = &num;

printf ("%d\n", num);

printf ("%d\n", numPtr);

printf ("%d\n", &num);

printf ("%d\n", *numPtr);

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