Introduction to C Memory Management and C++ Object-Oriented Programming

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C is used when 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 what the operating system allows.

Memory layout: process context

Accessing memory in C: pointers

Pointers are memory addresses.
Every variable has a memory address.
It‘s all about tracking which addresses are 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 are 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 you 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 have to allocate memory on heap.
When passing a parameter whose value you want to allow 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. are defined more than once!
Use #ifndef directive to define things only if they have 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 that function is included directly in the executable, allowing fuction 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

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Introduction to C Memory Management and C++ Object-Oriented Programming

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原文地址：http://www.cnblogs.com/codetravel/p/4534578.html

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Level of abstraction	Languages
Directly manipulate memory	Assembly(x86,MIPS)
Access to memory	C,C++
Memory managed	Java,C#,Scheme/Lisp,ML