CS2: SLP

Core rules of C

• All data has a place (somewhere in memory)

• All data has a size (sizeof tells byte size)

• Zero is special (end of strings and NULL)

built in versions of zero

• ‘\0’ for char

• 0 for int

Differences of Java and C

• Java is memory-managed, C is not

• Java is object-oriented and strongly types, C is not

• Java has built-in dynamic data structures, C does not

What ‘C programming is procedural’ means

• No classes or objects

• use of Global and local variables

• No exceptions but uses error codes

• has small, well-defined functions

Memory management

When the system manages your dynamically-allocated memory

Advantages of memory management

• Few details for programmer

• Code focuses on problem not allocation

• reduced risk of memory-related security issues

Disadvantages of memory management

• Less control and knowledge of what your program is doing

• difficult to identify performance issues by studying code

• difficult accessing hardware-specific low-level memory and registers

Characteristics of interpreted languages

• Runs within virtual machine providing standard environment

• Cross-platform compatible

• greater overhead therefore worse performance

Characteristics of compiled languages

• Native hardware instructions and conventions

• needs compilation for different platforms

• less overhead therefore better performance

Undefined behaviour

Behaviour, upon use of a nonportable or erroneous program construct or of erroneous data, for which this international standard imposes no requirements

Low-level and high-level languages

• High level language abstracts more details that are irrelevant to the problem

• Low level language requires programs to pay attention to irrelevant details

Static memory

Where memory allocation size is known at compile-time

Dynamic memory

Where memory allocation size is not known at compile-time

Places in which data must be located

• The stack

• The heap

• The data segment

The stack

Read-write, created/destroyed with function calls. Requires size known at compile-time

The heap

read-write, allocated from OS via syscall. Can handle size unknown at compile-time

The data segment

read-only, stores literals and constants within the process

Data sizes in C

• char: 1 byte

• short: 2 bytes

• int: 4 bytes

• float: 4 bytes

• long: 8 bytes

• double: 8 bytes

Arrays in C

• Laid out sequentially in memory

• can be static or dynamic

• they use pointer arithmetic

Decaying an array into a pointer

This is when a static array is passed to a function. the pointer to the starting element is passed and not the array as a whole

C compilation process

1. Preprocessing

2. Compilation

3. Assembly

4. Linking

Preprocessing

Prepares the raw code by removing comments, expanding macros and copying in header files.

• Input: source code .c

• output: expanded source code .i

Compilation

Checks the expanded code for syntax errors and translates high-level C logic into low-level instructions

• input: expanded source code .i

• output: assembly code .s

Assembly

Assembler translates human-readable instructions into raw, binary machine code the CPU understands

• Input: assembly code .s

• output: object code .o or .obj

Linking

Combines generated object code with external libraries and other object files to build final program

• input: object code .o + external libraries

• output: .exe or a.out

Declarations and Definitions

• Declaration of something indicates its name and type

• Definition of something indicates its name and type and reserves memory for it

When to use a Struct

This structure is used when you need to group related pieces of data that must all be stored maintained, and accessed simultaneously

When to use a Union

This is a structure used to conserve memory when having a variable that may be one of several types