What exactly is a pointer? In computer science, a pointer is a data item in many programming languages which stores a fixed memory location. This may be that of an index in memory mapped by the computer hardware, or else that of another data located externally on the hard drive.
The data that the pointer points to is then referred to as an address, and may be stored in the computer’s registry for later references. In other words, every instruction that the computer receives is preceded by the address that the processor has stored.
One of the main uses of pointers in C is the use of a keyword. You may have seen the var keyword mentioned a few times in the C programming languages. var refers to a local variable, which can be accessed by a local variable name. For example, if you are writing a function and want to assign a variable named x to the current time, you would write the code like this:
void my_a = allocate(sizeof(int), stdio.h strcpy(my_var); The above example creates a local variable var which will be accessed by my_was and later stored into the memory at address point PTR. In other words, the above example defines a pointer var, which can be accessed later by a function named my_var. Pointers are very useful in C because they allow programmers to pass data from one area of the program to another area of the program. For example, in the definition of the my_var above, the programmer can specify how much memory PTR will be used by my_var. As another example, the definition of the my_string function might look like this: typedef int string (char); void my_string (const char *); void my_fstring (string (const char* hello_string, const char* world_string, size (double), hello_string); void my_fstring (string (char const* hello_string, double, world_string); The above code creates a pointer, a char const* and a double, all of which can be later utilized in the my_string function.
A pointer is one of the types of memory addresses in the C language. However, it’s also used with different names depending on the function it’s defined for. One of the most common types of memory addresses is a static memory address, which refers to a single location within a program where that particular memory address is used. Another common type of memory address is a dynamic memory address, which refers to a single location within a program where multiple pointers to that location exist. A third common type of memory address is an array address, which can store a series of static or dynamic memory addresses in a single array. And finally, another common type of memory address is a function pointer, which is a single pointer to a function.
In the previous example, the my_string function defines a pointer p, which is a pointer to a function stored in the dynamic memory. It’s the job of the my_string function’s destructor to deallocate any allocated memory blocks it has created. When the my_string function returns, the destructor removes the pointer from the saved registers and then restores it to the registers that it was stored in before it was called. If there were two such functions defined for the same program, and both of them needed to exit at the same time, the programmer would have to remember two different addresses, and use the second one for the destruction of the first function.
Pointers are often used as indexes into data storage, but they can also be used as execution targets. What makes a pointer, a valid target for execution is the set of rules that defines the size and range of the pointers to values that will be accepted. This definition involves the values of the pointers, their types, and their use inside the code. The type of the pointer, along with the size of the allocation block, are important criteria. These factors, when combined with the rules defining how to access the data storage, define a valid target for an assignment, a function call, or return.
One common example of a valid target is a variable, which can be made const. This means that the value pointed to by a variable can never be changed before the declaration or definition of the variable. Another example is a pointer, which is defined as a non-constant variable. A const pointer will always point to the same location in memory as where it was originally defined. A pointer to a const or static variable will change only when the count keyword is used.
In this book, you will learn about the basics of C. You’ll explore pointers, their definition, and how to use them. You’ll discover why C developers write simple programs rather than difficult ones, and why simple data types are preferable to using complex ones. You’ll also learn about the value of a pointer, how to define a pointer, and what are the uses for pointers. With this book, you’ll learn how to become a skilled C programmer.