Introduction to C Memory Management and C + + object-oriented programming

• C is used if at least one of the following matters:
• Speed
• Memory
• Low-level features (moving the stack pointer, etc).

• Level of abstraction	Languages
  Directly Manipulate memory	Assembly (X86,mips)
  Access to Memory	C,c++
  Memory Managed	Java,c#,scheme/lisp,ml

  
  
• It ' s A memory world

Figure:processors read from Memory,do things, and write to memory.

• The heap is a chunk of memory for the C program to use.
• Can think of it as a giant array.
• Access hep Using special pointer syntax.
• The whole program, HS access to the heap depending, on the operating system allows.
• Memory layout:process Context

• accessing Memory in C:pointers
• pointers is memory addresses.
• Every variable has a memory address.
• It's all about tracking which addresses is still in use.
• Revisiting C Memory:stack vs. heap
• The C compiler lays out memory corresponding to functions (Arguments,variables) on the stack.
• C allows the programmer to allocate additional memory on the heap.

	Stack	Heap
Memory is allocated Memory is deallocated Addresses is assigned	Upon entering function Upon function return Statically	With malloc With free Dynamically

• Dynamic Allocation and deallocation
• Allocation
• int *p = malloc(sizeof(int));
• Deallocation
• free(p);
• Memory errors
• How can produce memory errors
• Program accesses memory it shouldn ' t (not yet allocated, not yet freed, past end of heap block, inaccessible parts of the Stack).
• Dangerous use of unitialized values.
• Memory leaks
• Bad frees.
• Manifestations of memory errors
• "Junk" values
• Segmentation Falult-program crashes.
• Tools for programming with memory
• GDB: the GNU Project Debugger
• Start your program, specifying things that might affect behavior.
• Make your program stop on breakpoints.
• Examine variables etc.at program points.
• Change things in your program while debugging.
• Valgrind: A Memory profiling tool
• A GPL System for debugging and profilling Linux programs.
• Tool Suite includes Memcheck, Cachegrind, Callgrind, massif, and Helgrind.
• Review:when to use pointers
• When you had to allocate the memory on heap.
• When passing a parameter whose value, the other function-to-change.
• Also for efficiency-to avoid copying data structures.
• A closer Look at the GCC compilation process
• Preprocessor
• Translation of # directives.
• Translates all macros (#DEFINE's) into inline C code.
• Takes #include files and inserts thm into the code.
• Get redefinition Error if structs etc. is defined more than once!
• Use #ifndef directive to define things only if they has not been defined.

#ifndef  _HEADER_NAME
#define _HEADER_NAME
/* Header code here. */
#endif

• Parsing and translation
• Translates to assembly, performing optimizations.
• Assembler
• Translates assembly to machine instructions.
• Linking
• Static. For each function called by the program, the assembly to this function is included directly in the executable, allowing Fu Ction calls to directly address code.
• Dynamic. Function calls call a Procedure Linkage Table, which contains the proper addresses of the mapped memory.

Some Helpful Compiler Options

Enforcements and warnings
-ansi -pedantic -wall -W	tells compiler to enforce ANSI C standards. More pedantic ANSI with warnings. Shows all warnings. Show some warnings (return without a value, etc.).
Compilation/output
-C -S -E -O [File]	Compile and assemble,but do not link. Stop after compilation; Do not assemble. Stop after preprocessing; Do not compile. Put the output binary in [file].
Profiling
-pg	Compile with profiling information

From for notes (Wiz)

Introduction to C Memory Management and C + + object-oriented programming