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Oh crap! I forgot (or
 never learned) C!
       Chris Adamson
       CodeMash 2010
Objective- C is defined as a small but powerful set of
   extensions to the standard ANSI C language. […]
  Objective-C is designed to give C full object- oriented
programming capabilities, and to do so in a simple and
                   straightforward way.
“Here, John Parker, take
this wheel. It drives just
like a truck.”
“Here, John Parker, take
this wheel. It drives just
like a truck.”


“Good. What is a truck?”
*
**
&
WTF?
Don’t
Panic!
Don’t
   Panic!
You can do this!
1972
1978, 1988
http://
http://
http://
http://
http://www.langpop.com/
Why does C matter
     today?
Libraries with C inside

Linux kernel (C, assembly), GNU libraries (C, C++)
OpenGL, OpenAL, SQLite, PostgreSQL, …
Way more than I can list here:
   http://directory.fsf.org/category/clibs/
Languages that need C

Interpreters and VMs written in C:
   Ruby, PHP, Perl, Java
Typically, you’ll use C to call into native libraries from these
languages (e.g., Java Native Interface)
Even on iPhone

Some essential iPhone libraries are C-only:
   OpenGL, OpenAL
   Core Audio, Core Graphics, Core Foundation
   Keychain, Address Book, System Configuration
C’s descendents

Languages inspired by C or directly based on it are the
dominant languages for systems, application, and mobile
development:
C++, Objective-C, Java, C# [?]
   Can we call these the *C* languages?
Why C?
C’s traits

Minimal: no fluff!
Portable: nearly every OS has a C compiler
Performant!
C performance




http://gmarceau.qc.ca/blog/2009/05/speed-size-and-
               dependability-of.html
C performance




http://gmarceau.qc.ca/blog/2009/05/speed-size-and-
               dependability-of.html
C performance




http://gmarceau.qc.ca/blog/2009/05/speed-size-and-
               dependability-of.html
C performance




http://gmarceau.qc.ca/blog/2009/05/speed-size-and-
               dependability-of.html
C performance




http://gmarceau.qc.ca/blog/2009/05/speed-size-and-
               dependability-of.html
C performance




http://gmarceau.qc.ca/blog/2009/05/speed-size-and-
               dependability-of.html
Is C a high-level
   language?
Abstractions
Abstractions
Abstractions
CPU abstraction


int x = 5;
int y = 10;
int z = x + y;
CPU abstraction

                     .loc   1 38 0
                     movl   $5, -12(%ebp)
                     .loc   1 39 0
int x = 5;           movl   $10, -16(%ebp)
int y = 10;          .loc   1 40 0
int z = x + y;       movl   -16(%ebp), %eax
                     addl   -12(%ebp), %eax
                     movl   %eax, -20(%ebp)

                            Intel x86
CPU abstraction


int x = 5;
int y = 10;
int z = x + y;
CPU abstraction

                     add   r0,   sp, #24
                     add   r3,   sp, #16
int x = 5;           add   r2,   sp, #20
                     ldr   r1,   [r3]
int y = 10;          ldr   r3,   [r2]
int z = x + y;       add   r3,   r1, r3
                     str   r3,   [r0]

                            ARM
Memory abstraction

Memory may be dynamically allocated and freed
   malloc(), free()
No garbage collection or other automated memory
management techniques
   Libraries and later languages add this
“High” or “Low” level

Old CW: Abstracting away the CPU makes you high-level
   Effectively, anything other than assembly was high-level
New CW: Abstracting away the memory makes you high-level
   C in 2010 is what assembly was in 1980
So why should I learn C?

Pro: You may have to use it for something
   Embedded systems, native code calls, highly portable
Con: You probably won’t be as productive
   Lower abstraction cost implies lower abstraction value
How do you (re-)learn C?
C is rarely anyone’s first language
   I learned a variety of BASICs, Pascal, and assembly first
   If you’re at CodeMash, you likely know one or more C-
   inspired languages
       Direct descendants: C++, Java, csh
       Distant relatives: Python, Ruby, other shells
Smoke ‘em if you got ‘em
Your language probably has traits in common with C
   Control structures, parameters and return values, etc.
Your language probably added stuff that C doesn’t have
   Objects
   Garbage Collection
   Closures, type-safety, generics, …
C is so primitive!
We’re gonna learn to hunt
Primitive C
The absolute basics

C source is compiled directly into a machine-executable
binary
As far as the compiler cares, your C program could be one
big listing
Execution starts inside the main() function
Headers and includes

By convention, we use separate header and source files
   Header (.h) includes public information: function names,
   constants, and other stuff needed by callers
   Source (.c, .cpp, .m, .mm) includes implementation code
       Use #include to include header when compiling
“Hello World” in C

  #include <stdio.h>

  int main() {

      printf ("Hello world!");

  }
C expressions

Expression is a combination of operators and operands
   x + 1 has one operator (+) and two operands (x, 1)
Mathematical operators: +, -, *, /, %, >>, <<, >>>
Logical operators: !, &, |, &&, ||, <, >, <=, >=, !=, ?:
   Use parentheses for ordering: a+b*c vs (a+b)*c
C types
Integer types: short, int, long, long long
   int and long may be “unsigned”
Floating-point types: float, double
Other types: char, bool
Absence of type: void
Bit depth of numeric types is undefined
Type conversion
Expressions that combine types implicitly change them
   char, short convert to int
   floats convert to double
   ints convert to long
   unsigned becomes signed
   all other cases: everything’s an int
Assignment
Declare a variable of a type, then assign its value as the
result of an expression

                 int x;
                 x = 3;

                 x = x + 1
                 x += 1;
                 x++;
Assignment from functions
Can also use a function call to assign a value
Can combine these

          int x;
          x = abs (rand() % 5);
Creating a function
 Declare return type, name, parameter types and names


double circumference (double r) {
    return 2 * 3.14159 * r;
}
Variable scope
C variables use lexical scope: only available within the
function in which they’re declared
   Variables with same name in different scope are different
   variables
Variables declared outside the scope of any function are
“global variables”, and are available anywhere
   Try not to use them much, if at all
Pass by value
What is the value of y?

         int addOne (int x) {
           return x+1;
         }

         int y = 0;
         int z = addOne (y);
Pass by value
What is the value of y?

         int addOne (int x) {
           return x+1;
         }

         int y = 0;
         int z = addOne (y);


y is still 0. The function gets y’s value (0), not the y
variable itself
Flow Control: if-else
    if (expression)
      // execute statement if true
    else
      // execute statement if false


“true” means “non-zero”
Executes only one statement for each branch; use curly-
braces to do more
Flow-control: switch
switch (expression) {
  case value1:
      // statements
      break;
  case value2:
      // statements
      break;
  // other cases
  default:
      // statements execute in any case
}
Flow-control: while

     while (expression)
     // statement

     do
     // statement
     while (expression);
Flow-control: for

for (initExpression;
      continueExpression;
      countingExpression)
// statement
Flow-control: break

break terminates innermost for, while, do, or switch
return exits from a function, with a value if function declares
one
goto jumps to a labelled line of code
   “Go To statement considered harmful”, 1968
Complex types
enums
 enum {HEARTS, DIAMONDS, CLUBS, SPADES};

A list of constant int values
Starts at 0 and increments, unless you assign specific values
with =
Alternative: use #define preprocessor directive

           #define HEARTS 1
           #define DIAMONDS 2
New types: typedef

    Allows you to define new type names for variables
    By convention, typedef names are capitalized

typedef enum {HEARTS, DIAMONDS, CLUBS, SPADES} SuitType;

int main() {
  SuitType suit = DIAMONDS;
}
Structs

Creates “structure” consisting of several named members of
various types
Access members with dot operator
Really tempting to call it an “object”, but…
Structs aren’t objects
Structs aren’t objects

    struct CGPoint {
       CGFloat x;
       CGFloat y;
    };
    typedef struct CGPoint CGPoint;
Structs aren’t objects
Structs aren’t objects
  void addToPointX (CGPoint aPoint) {
    aPoint.x += 10;
  }
Structs aren’t objects
  void addToPointX (CGPoint aPoint) {
    aPoint.x += 10;
  }

  CGPoint point;
  point.x=0;
  point.y=0;
  addToPointX (point);
Structs aren’t objects
     void addToPointX (CGPoint aPoint) {
       aPoint.x += 10;
     }

     CGPoint point;
     point.x=0;
     point.y=0;
     addToPointX (point);

point.x is still 0, because the whole CGPoint is a value,
                        not an object
Arrays
Indexed access to multiple instances of a type
Declare with [] and size of array
Access an index with [index]
   First member is index=0

       Card deck[52];
       Card topCard = deck[0];
Character arrays / strings
An array of type char is a string
   Terminated by a null character (/0)
Can declare literals with “” operator
Conveys no information about encoding, typically assumed
to be ASCII

 char confName[] = "CodeMash";
This is where it gets
        scary
Arrays are syntactic sugar

Array is just a reference to a location in memory
Index is an offset
   No bounds checking!
Pointers
A pointer is literally a memory address, interpreted as a
reference to a variable at that memory address
Indicated with the * character
Pointers
A pointer is literally a memory address, interpreted as a
reference to a variable at that memory address
Indicated with the * character


 char confName[] = "CodeMash";
Pointers
A pointer is literally a memory address, interpreted as a
reference to a variable at that memory address
Indicated with the * character
Pointers
A pointer is literally a memory address, interpreted as a
reference to a variable at that memory address
Indicated with the * character


 char *confName = "CodeMash";
Using pointers
A pointer to a variable is used like any other variable of that
type
Access to members of a pointed-to struct use the -> operator
A function that takes a pointer parameter or returns a
pointer declares * on the type
To refer to the address of a pointer, use &
Pointer example
Pointer example
void reallyAddToPointX (CGPoint *aPoint) {
  aPoint->x += 10;
}
Pointer example
void reallyAddToPointX (CGPoint *aPoint) {
  aPoint->x += 10;
}

CGPoint point;
point.x=0;
point.y=0;
reallyAddToPointX (&point);
Pointer example
void reallyAddToPointX (CGPoint *aPoint) {
  aPoint->x += 10;
}

CGPoint point;
point.x=0;
point.y=0;
reallyAddToPointX (&point);


             point.x is now 10.0
Allocating memory

Allocate memory with malloc()
   The amount you need can be determined with sizeof()
   Return value is a pointer to allocated memory
Release memory with free()
malloc() example
CGPoint point;
point.x=0;
point.y=0;
reallyAddToPointX (&point);
malloc() example
CGPoint point;
point.x=0;
point.y=0;
reallyAddToPointX (&point);

CGPoint *point = malloc(sizeof(CGPoint));
point->x=0;
point->y=0;
reallyAddToPointX (point);
malloc() example
CGPoint point;
point.x=0;
point.y=0;
reallyAddToPointX (&point);

CGPoint *point = malloc(sizeof(CGPoint));
point->x=0;
point->y=0;
reallyAddToPointX (point);
free (point);
How to crash instantly

Use a bogus address in a pointer
         CGPoint *point = 42;
         point->x = 0;
How to crash instantly

      Use a bogus address in a pointer
                  CGPoint *point = 42;
                  point->x = 0;
Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x000000000000002a
Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Application Specific Information:
iPhone Simulator 3.1 (139.1), iPhone OS 3.1.2 (7D11)

Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0   CGPointCheck                   0x00002854 -[CGPointCheckViewController
viewDidLoad] + 72 (CGPointCheckViewController.m:53)
More memory functions

Copy blocks of memory with memcpy()
Set a block of memory with memset()
   Often used to “zero out” a buffer
Address arithmetic
Some memory functions require you to compute memory
locations manually
   Assume array a of type t
   Index n is at a + (n * sizeof(t))
Address arithmetic
  Some memory functions require you to compute memory
  locations manually
     Assume array a of type t
     Index n is at a + (n * sizeof(t))

memcpy(ioData->mBuffers[currentBuffer].mData +
         (currentFrame * 4) + (currentChannel*2),
   &sample,
   sizeof(AudioSampleType));
I/O parameters
C’s version of multiple return values
You pass in a pointer, it gets populated when function
returns
    OSStatus AudioUnitGetProperty (
       AudioUnit            inUnit,
       AudioUnitPropertyID inID,
       AudioUnitScope       inScope,
       AudioUnitElement     inElement,
       void                 *outData,
       UInt32               *ioDataSize
    );
That’s It
Things to take away
C is still popular for good reasons
   C’s performance and portability are building blocks for
   languages and libraries
   Lingua franca: everybody used to know it. Maybe
   everyone still should.
Thinking about memory can be a good thing!
When you have questions

Kernighan & Ritchie, The C Programming
Language, Prentice-Hall, 1988 (yes, really)
comp.lang.c
stackoverflow.com
Sample code!
Or just bug me

Web: http://www.subfurther.com
Blog: http://www.subfurther.com/blog
E-mail: invalidname@gmail.com
Twitter: @invalidname

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Oh Crap, I Forgot (Or Never Learned) C! [CodeMash 2010]

  • 1. Oh crap! I forgot (or never learned) C! Chris Adamson CodeMash 2010
  • 2.
  • 3. Objective- C is defined as a small but powerful set of extensions to the standard ANSI C language. […] Objective-C is designed to give C full object- oriented programming capabilities, and to do so in a simple and straightforward way.
  • 4.
  • 5. “Here, John Parker, take this wheel. It drives just like a truck.”
  • 6. “Here, John Parker, take this wheel. It drives just like a truck.” “Good. What is a truck?”
  • 7.
  • 8.
  • 9.
  • 10.
  • 11.
  • 12.
  • 13.
  • 14.
  • 15. *
  • 16. **
  • 17. &
  • 18. WTF?
  • 20. Don’t Panic! You can do this!
  • 21. 1972
  • 23.
  • 29. Why does C matter today?
  • 30. Libraries with C inside Linux kernel (C, assembly), GNU libraries (C, C++) OpenGL, OpenAL, SQLite, PostgreSQL, … Way more than I can list here: http://directory.fsf.org/category/clibs/
  • 31. Languages that need C Interpreters and VMs written in C: Ruby, PHP, Perl, Java Typically, you’ll use C to call into native libraries from these languages (e.g., Java Native Interface)
  • 32. Even on iPhone Some essential iPhone libraries are C-only: OpenGL, OpenAL Core Audio, Core Graphics, Core Foundation Keychain, Address Book, System Configuration
  • 33. C’s descendents Languages inspired by C or directly based on it are the dominant languages for systems, application, and mobile development: C++, Objective-C, Java, C# [?] Can we call these the *C* languages?
  • 35. C’s traits Minimal: no fluff! Portable: nearly every OS has a C compiler Performant!
  • 42. Is C a high-level language?
  • 46. CPU abstraction int x = 5; int y = 10; int z = x + y;
  • 47. CPU abstraction .loc 1 38 0 movl $5, -12(%ebp) .loc 1 39 0 int x = 5; movl $10, -16(%ebp) int y = 10; .loc 1 40 0 int z = x + y; movl -16(%ebp), %eax addl -12(%ebp), %eax movl %eax, -20(%ebp) Intel x86
  • 48. CPU abstraction int x = 5; int y = 10; int z = x + y;
  • 49. CPU abstraction add r0, sp, #24 add r3, sp, #16 int x = 5; add r2, sp, #20 ldr r1, [r3] int y = 10; ldr r3, [r2] int z = x + y; add r3, r1, r3 str r3, [r0] ARM
  • 50. Memory abstraction Memory may be dynamically allocated and freed malloc(), free() No garbage collection or other automated memory management techniques Libraries and later languages add this
  • 51. “High” or “Low” level Old CW: Abstracting away the CPU makes you high-level Effectively, anything other than assembly was high-level New CW: Abstracting away the memory makes you high-level C in 2010 is what assembly was in 1980
  • 52. So why should I learn C? Pro: You may have to use it for something Embedded systems, native code calls, highly portable Con: You probably won’t be as productive Lower abstraction cost implies lower abstraction value
  • 53. How do you (re-)learn C? C is rarely anyone’s first language I learned a variety of BASICs, Pascal, and assembly first If you’re at CodeMash, you likely know one or more C- inspired languages Direct descendants: C++, Java, csh Distant relatives: Python, Ruby, other shells
  • 54. Smoke ‘em if you got ‘em Your language probably has traits in common with C Control structures, parameters and return values, etc. Your language probably added stuff that C doesn’t have Objects Garbage Collection Closures, type-safety, generics, …
  • 55. C is so primitive!
  • 58. The absolute basics C source is compiled directly into a machine-executable binary As far as the compiler cares, your C program could be one big listing Execution starts inside the main() function
  • 59. Headers and includes By convention, we use separate header and source files Header (.h) includes public information: function names, constants, and other stuff needed by callers Source (.c, .cpp, .m, .mm) includes implementation code Use #include to include header when compiling
  • 60. “Hello World” in C #include <stdio.h> int main() { printf ("Hello world!"); }
  • 61. C expressions Expression is a combination of operators and operands x + 1 has one operator (+) and two operands (x, 1) Mathematical operators: +, -, *, /, %, >>, <<, >>> Logical operators: !, &, |, &&, ||, <, >, <=, >=, !=, ?: Use parentheses for ordering: a+b*c vs (a+b)*c
  • 62. C types Integer types: short, int, long, long long int and long may be “unsigned” Floating-point types: float, double Other types: char, bool Absence of type: void Bit depth of numeric types is undefined
  • 63. Type conversion Expressions that combine types implicitly change them char, short convert to int floats convert to double ints convert to long unsigned becomes signed all other cases: everything’s an int
  • 64. Assignment Declare a variable of a type, then assign its value as the result of an expression int x; x = 3; x = x + 1 x += 1; x++;
  • 65. Assignment from functions Can also use a function call to assign a value Can combine these int x; x = abs (rand() % 5);
  • 66. Creating a function Declare return type, name, parameter types and names double circumference (double r) { return 2 * 3.14159 * r; }
  • 67. Variable scope C variables use lexical scope: only available within the function in which they’re declared Variables with same name in different scope are different variables Variables declared outside the scope of any function are “global variables”, and are available anywhere Try not to use them much, if at all
  • 68. Pass by value What is the value of y? int addOne (int x) { return x+1; } int y = 0; int z = addOne (y);
  • 69. Pass by value What is the value of y? int addOne (int x) { return x+1; } int y = 0; int z = addOne (y); y is still 0. The function gets y’s value (0), not the y variable itself
  • 70. Flow Control: if-else if (expression) // execute statement if true else // execute statement if false “true” means “non-zero” Executes only one statement for each branch; use curly- braces to do more
  • 71. Flow-control: switch switch (expression) { case value1: // statements break; case value2: // statements break; // other cases default: // statements execute in any case }
  • 72. Flow-control: while while (expression) // statement do // statement while (expression);
  • 73. Flow-control: for for (initExpression; continueExpression; countingExpression) // statement
  • 74. Flow-control: break break terminates innermost for, while, do, or switch return exits from a function, with a value if function declares one goto jumps to a labelled line of code “Go To statement considered harmful”, 1968
  • 76. enums enum {HEARTS, DIAMONDS, CLUBS, SPADES}; A list of constant int values Starts at 0 and increments, unless you assign specific values with = Alternative: use #define preprocessor directive #define HEARTS 1 #define DIAMONDS 2
  • 77. New types: typedef Allows you to define new type names for variables By convention, typedef names are capitalized typedef enum {HEARTS, DIAMONDS, CLUBS, SPADES} SuitType; int main() { SuitType suit = DIAMONDS; }
  • 78. Structs Creates “structure” consisting of several named members of various types Access members with dot operator Really tempting to call it an “object”, but…
  • 80. Structs aren’t objects struct CGPoint { CGFloat x; CGFloat y; }; typedef struct CGPoint CGPoint;
  • 82. Structs aren’t objects void addToPointX (CGPoint aPoint) { aPoint.x += 10; }
  • 83. Structs aren’t objects void addToPointX (CGPoint aPoint) { aPoint.x += 10; } CGPoint point; point.x=0; point.y=0; addToPointX (point);
  • 84. Structs aren’t objects void addToPointX (CGPoint aPoint) { aPoint.x += 10; } CGPoint point; point.x=0; point.y=0; addToPointX (point); point.x is still 0, because the whole CGPoint is a value, not an object
  • 85. Arrays Indexed access to multiple instances of a type Declare with [] and size of array Access an index with [index] First member is index=0 Card deck[52]; Card topCard = deck[0];
  • 86. Character arrays / strings An array of type char is a string Terminated by a null character (/0) Can declare literals with “” operator Conveys no information about encoding, typically assumed to be ASCII char confName[] = "CodeMash";
  • 87. This is where it gets scary
  • 88. Arrays are syntactic sugar Array is just a reference to a location in memory Index is an offset No bounds checking!
  • 89. Pointers A pointer is literally a memory address, interpreted as a reference to a variable at that memory address Indicated with the * character
  • 90. Pointers A pointer is literally a memory address, interpreted as a reference to a variable at that memory address Indicated with the * character char confName[] = "CodeMash";
  • 91. Pointers A pointer is literally a memory address, interpreted as a reference to a variable at that memory address Indicated with the * character
  • 92. Pointers A pointer is literally a memory address, interpreted as a reference to a variable at that memory address Indicated with the * character char *confName = "CodeMash";
  • 93. Using pointers A pointer to a variable is used like any other variable of that type Access to members of a pointed-to struct use the -> operator A function that takes a pointer parameter or returns a pointer declares * on the type To refer to the address of a pointer, use &
  • 95. Pointer example void reallyAddToPointX (CGPoint *aPoint) { aPoint->x += 10; }
  • 96. Pointer example void reallyAddToPointX (CGPoint *aPoint) { aPoint->x += 10; } CGPoint point; point.x=0; point.y=0; reallyAddToPointX (&point);
  • 97. Pointer example void reallyAddToPointX (CGPoint *aPoint) { aPoint->x += 10; } CGPoint point; point.x=0; point.y=0; reallyAddToPointX (&point); point.x is now 10.0
  • 98. Allocating memory Allocate memory with malloc() The amount you need can be determined with sizeof() Return value is a pointer to allocated memory Release memory with free()
  • 100. malloc() example CGPoint point; point.x=0; point.y=0; reallyAddToPointX (&point); CGPoint *point = malloc(sizeof(CGPoint)); point->x=0; point->y=0; reallyAddToPointX (point);
  • 101. malloc() example CGPoint point; point.x=0; point.y=0; reallyAddToPointX (&point); CGPoint *point = malloc(sizeof(CGPoint)); point->x=0; point->y=0; reallyAddToPointX (point); free (point);
  • 102. How to crash instantly Use a bogus address in a pointer CGPoint *point = 42; point->x = 0;
  • 103. How to crash instantly Use a bogus address in a pointer CGPoint *point = 42; point->x = 0; Exception Type: EXC_BAD_ACCESS (SIGBUS) Exception Codes: KERN_PROTECTION_FAILURE at 0x000000000000002a Crashed Thread: 0 Dispatch queue: com.apple.main-thread Application Specific Information: iPhone Simulator 3.1 (139.1), iPhone OS 3.1.2 (7D11) Thread 0 Crashed: Dispatch queue: com.apple.main-thread 0 CGPointCheck 0x00002854 -[CGPointCheckViewController viewDidLoad] + 72 (CGPointCheckViewController.m:53)
  • 104. More memory functions Copy blocks of memory with memcpy() Set a block of memory with memset() Often used to “zero out” a buffer
  • 105. Address arithmetic Some memory functions require you to compute memory locations manually Assume array a of type t Index n is at a + (n * sizeof(t))
  • 106. Address arithmetic Some memory functions require you to compute memory locations manually Assume array a of type t Index n is at a + (n * sizeof(t)) memcpy(ioData->mBuffers[currentBuffer].mData + (currentFrame * 4) + (currentChannel*2), &sample, sizeof(AudioSampleType));
  • 107. I/O parameters C’s version of multiple return values You pass in a pointer, it gets populated when function returns OSStatus AudioUnitGetProperty ( AudioUnit inUnit, AudioUnitPropertyID inID, AudioUnitScope inScope, AudioUnitElement inElement, void *outData, UInt32 *ioDataSize );
  • 109. Things to take away C is still popular for good reasons C’s performance and portability are building blocks for languages and libraries Lingua franca: everybody used to know it. Maybe everyone still should. Thinking about memory can be a good thing!
  • 110. When you have questions Kernighan & Ritchie, The C Programming Language, Prentice-Hall, 1988 (yes, really) comp.lang.c stackoverflow.com Sample code!
  • 111. Or just bug me Web: http://www.subfurther.com Blog: http://www.subfurther.com/blog E-mail: invalidname@gmail.com Twitter: @invalidname