Programming Practice: Data Representation in Memory

• Memory
  • basic abstraction: array addressable of bytes
  • an area of memory can change to different width
    • width based on context
    • same area of memory can access to different width
  • content of memory represent to 4 possibility:
    • undefined
    • data
    • program instruction
    • address to another memory location
  • what happen when you create a local variable
    • you receive access to a memory space for that variable
    • you can use that local name to access and modify the space
    • if you do not initialize the variable, the memory space store an arbitrary/random/unknown data;  so always initialize it!
    • name of the array is a pointer to the first value storage address
    • add and subtraction can apply to address
      • ex. int x[4], *xprt = x
        • x+2 = &x[2]
        • *(x+2) = x[2]
        • xptr += 2 = x[2]
        • illegal: x+=2
    • sizeof() function—return a int represent how much byte the data type used in memory
    • 
    • datatype size vary in size, depending on architecture and compiler
      • solution: use data type with known size
        • ex. <inttypes.h>