Since every byte of memory has a unique address, a variable's address is then determined by the first byte allocated to that variable. This type of polymorphism is used in the standard library when file I/O functions are called.Ī similar mechanism can also be used for implementing a state machine in C.Note: This article assumes that you have basic knowledge of programming.Įvery variable is allocated a section of memory big enough to hold a value of the variable's data type. A class is defined by extending the second structure with the data specific for the class, and static variable of the type of the first structure, containing the addresses of the functions that are associated with the class. A second base object structure containing a pointer to the previous First one declares a structure having as elements function pointers for the various operations to that can be specified polymorphically. Some implementations may require specifically casting the argument to the MyFunctionType type, even though the function signature exacly matches that of the typedef.įunction pointers can be useful for implementing a form of polymorphism in C. Some versions of C may not require an ampersand preceding the TalkJive argument in the DoSomethingNice call. Struct MyStruct DoSomethingNice ( 41, & TalkJive, & sillyStuff ) In the following code, the call to calloc() effectively allocates an array of struct MyStruct items.
The second case often occurs when accessing dynamically allocated memory. The function declares the parameter as a pointer, but the actual argument may be the name of an array. The first case often is seen to occur when an array is passed as an argument to a function.
#Pointer size in c code
You are quite free to write code that accesses memory outside that which you have explicitly requested from the system. A common cause of this is failure to initialize a pointer before trying to dereference it.Ĭ is known for giving you just enough rope to hang yourself, and pointer dereferencing is a prime example. The error is often reported as a segmentation error.
When dereferencing a pointer that points to an invalid memory location, an error often occurs which results in the program terminating. There is one more way of dereferencing a pointer, which will be discussed in the following section. They both access the m_aNumber element of the structure pointed to by bb. The expression bb->m_aNumber is entirely equivalent to (*bb).m_aNumber. m_aNumber = 3 /* assigns 3 to the m_aNumber member of astruct */ bb -> num2 = 44.3 /* assigns 44.3 to the num2 member of astruct */ * pj = bb -> m_aNumber /* equivalent to d = astruct.m_aNumber */ Int c, d int * pj struct MyStruct astruct struct MyStruct * bb c = 10 pj = & c /* pj points to c */ d = * pj /* d is assigned the value to which pj points, 10 */ pj = & d /* now points to d */ * pj = 12 /* d is now 12 */ bb = & astruct ( * bb ).