A Mutable Log

A blog by Devendra Tewari

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Points to remember regarding C pointers

Some points to remember regarding C pointers

  1. A pointer is like any value type, but the value it stores is an address, that is why pointers to any type have the same size i.e. value returned by sizeof is the same.

  2. A pointer can store the address of another pointer, thus the existence of **.

  3. If defined within a function its scope is auto, it is created on the stack and dies when the function returns.

  4. If passed to another function i.e. callee, the value it stores i.e. the address it points to, is passed to the callee.

  5. To gain access to the value it points to, a pointer has to be dereferenced, this is done by using the * operator.

  6. A pointer that has a value of 0 is called a null pointer.

  7. To get the address of any identifier, the & operator can be used. Don’t pass pointer to a variable of scope auto to a callee that may retain it for use at some future point in time. Once the caller returns, the region of stack used by it is reclaimed, the callee may read values that are, for all effects, junk.

  8. Pointer arithmetic can be used to read array elements, when you add n to a pointer, you are traversing to the nth element in the array.

  9. A pointer may be cast to a struct pointer, and the attributes of the struct read or written to. Beware of byte ordering i.e. endianness, and struct memory alignment, when you memcpy data between devices with different processor architectures. Usage of appropriate compiler directive, packed attribute of GCC for instance, is recommended to prevent padding from causing issues e.g.
    • struct __attribute__ ((__packed__)) identifier {... OR
    • typedef struct {...} __attribute__ ((__packed__)) identifier... OR
    • #pragma pack(1)
  10. A void * is used to store the address of any arbitrary type.