Transcript Introduction to Programming in C / C++ / ROOT

Introduction to Programming
in C / C++ / ROOT
Christopher Crawford
2008-10-01
Computer Architecture
ALU
Cache
Registers
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CPU
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(32/64 bit words)
Instructions
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Read / Write / Arithmetic
Branching / Subroutines
Registers
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Program counter
Stack counter (subroutines)
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Pre-emptive multitasking
Memory – bytes (8 bit bytes)
- Address space (address, data):
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data (variables)
text (CPU instructions)
I/O (not memory at all)
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Virtual memory (paging)
Input / Output
(N-bit buses)
- busses
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PCI- expansion slots, Ethernet
IDE, SATA - hard drive (HD)
USB – keyboard, mouse
LPC - serial, parallel, floppy
IRQ – interrupt requests
DMA – direct memory access
Operating System
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BIOS – first instructions executed,
loads and runs OS kernel
Process control
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Paging (swap space)
Segmentation violations!
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File system
All external data mounted into
common directory tree
Devices are treated as files
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Device drivers, accesses I/O
programs which further interact with
kernel (process, mem, i/o)
Eg.: ls, cd, cp, mv, ps, mount, etc
Compiler
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Compiler chain
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/dev/ttyS1
/dev/stdin, /dev/stdout )
Modules
User interface to the kernel
Interpreted ‘language’
Shell scripts
Eg.: bash, tcsh, tcl, perl
Utilities
I/O devices
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Memory management
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Scheduler (multitasking)
Environment for processes
Threads (separate execution lines
in a single program
Shell
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Kernel – controls CPU
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(#include)
(.c  .s)
(.s  .o)
(.o  .so, a.out)
(.so, a.out  memory)
Build tool chain
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Preprocessor
Compiler
Assembler
Linker
Loader
Configure
Make
Debugging
Libraries:
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Std C library
(autoconf)
(automake)
(gdb, gprof)
*.so *.a *.h
(glibc)
File System
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All I/O is organized into one tree
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Path: parent/child/grandchild/…
Mounts: (instead of a: b: c: drives)
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Drivers, raw I/O: /dev
Kernel I/O:
/proc, /sys
Special directories
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Single disk at base of file system
Other disks ‘mounted’ (grafted)
onto branches of file system
Root (base)
Current (cwd)
Parent
Home ($HOME)
/
.
..
~
Directory structure
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Std names for common
directories
bin, etc, lib, include, share, src
Repeating hierarchy of structure
/, /usr, /usr/local, /usr/X11, /opt,
...
/
etc
bin
(binaries)
sbin
lib
var
..
tmp
- root directory
- configuration
- executable
- secure code
- libraries
- databases, spools,
- temporary files
boot/
- kernel image
mnt/ usb,floppy
- mounted directories
dev/
- I/O devices
zero,null,ttyS0,parport0
std{in,out,err} ->
/proc/self/fd/{0,1,2}
sca,sca0,sca1, scb,scb0, ..,
cdrom -> scd0
proc/
- CPU processes
cpuinfo,meminfo, - diagnostics
16117/cwd,environ,cmdline
fd/{0,1,2} -> /dev/pts/{0,1,2}
sys/
- system info
usr/bin,lib,share…
software
local/bin,lib,…
X11/bin,lib,…
opt/
- distribution
- custom software
- GUI software
- commercial software
root/
- superuser directory
home/
- user directories
chris2/ etc,bin,lib
data/
- shared data
bash – Bourne-again shell
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Program execution
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ENVIRONMENT variables
1. grep
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Input / Output redirection
2. find
Utilities
3. sed
Memory structure
Address Space
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Size in bytes (not words)
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type
symbol
address
data
(C/C++)
(assembly)
(hardware)
(hardware)
Text (code)
Data (globals)
Stack (auto,temp)
Heap (dynamic)
Type modifiers:
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auto, static, extern
const, volatile
[un]signed
Discrete
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4 GB (32 bit pointers)
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bool
char
short
integer
long long
2
256
65536
4.295G
18.447E
1 bit
8 bits
16 bits
32 bits
64 bits
1 byte
2 bytes
4 bytes
8 bytes
1 word
2 words
7e-7
2e-16
32 bits
64 bits
4 bytes
8 bytes
1 word
2 words
Continuous
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Program parts:
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Memory chart:
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Data Types
float
double
Compound
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void
pointers
references
arrays
structures
none (no type)
32/64 CPU dependent
0 alias only
N * base type
Σ base types
Sample C program
#include <stdio.h>
#include <string.h>
/* library function prototypes */
int n = 1;
float x = 2.3;
/* variable declarations */
int add( float x, float y );
/* function prototype */
int main( int argc, char** argv )
{
int y = add( n, x );
y = y + 1;
printf("y = %d\n", y);
/* main program */
char name[80];
printf( "who are you?\n" );
fgets( name, 80, stdin );
if (!strcmp( name, "joe\n" )) {
int i;
for ( i=0; i<5; ++i ) {
printf( "go away!\n" );
}
}
else {
printf( "hello, %s", name );
}
return 0;
/* automatic variable declaration */
/* statement with assignment operator */
/* formatted print statement */
/* character string (array) declaration */
/* conditional branching */
/* loop */
/* return value of function */
}
int add( float x, float y )
{
return x + y;
}
/* subroutine function */
Structure of a C program
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Essentially a collection of
declarations and definitions
of variables and functions
A. Expressions
Execution starts at
B. Blocks – group of statements
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Types are defined in the
same way they are used
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Strongly typed
Compiler only scans file once
int fn ( float var, …)
Function definitions are lists of
variable declarations and
statements executed linearly
Statements consist of
a) Expressions, b) Blocks, c) Flow Control
variables and constants tied
together with operators (functions)
{ statement; statement; ... }
int main ( int argc, char** argv) {
Everything must be defined
before it is used
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C. Flow control Statements
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Conditionals
if (cond) statement else statement
switch (key) {
case label: statement; break;
default: statement; }
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Loops
while (cond) statement
do statement while (cond);
for (init; cond; incr) statement
break; continue; (inside loops)
goto label;
label: statement
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Exceptions
try statement
catch (err) statement
throw err;
C/C++ punctuation
/* */
//
C-style comments
C++-style comments
{}
[]
()
<>
statement block, array initializer data
array index, declaration
function arguments, expression ordering, initializer
templates, #include <stdlib.h>
"string"
'c'
character string
single character
,
;
:
#
separates function arguments
end of statements and declarations
statement label
preprocessor directives
A-Za-z_0-9
valid characters in a name, first letter cannot be 0-9
C/C++ Operators – precedence & associativity
::
(unary <-, binary ->)
() [] -> .
->
++ -- + - ! ~
(unary) <(type) * & sizeof
.* ->*
->
* / %
->
+ ->
<< >>
->
< <= > >=
->
== !=
->
&
->
^
->
|
->
&&
->
||
->
?:
<= += -= *= /= %=
<&= ^= |= <<= >>=
,
->
scope
arguments, element, index, member
inc/decrement, pos., neg., not, complement
typecast, dereference, address, size
function pointer
multiply, divide, modulo
add, subtract
bit shift left/right; (stream insert/extract)
comparison
test equality
bitwise and
"
xor
"
or
logical and
"
or
if-then-else
assignment
sequence
IEEE Floating Point Numbers
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Integers
Standard C library – glibc
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<complex.h>
<math.h>
<signal.h>
<stdarg.h>
<stdio.h>
<stdlib.h>
<string.h>
<time.h>
– complex number arithmetic and functions
– trigonometric and exponential functions
– signal handling
– functions with indefinite # of arguments
– standard input / output
– memory allocation, process control, conversions, random numbers
– string comparison, memory copying
– time and date manipulation and formatting
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<assert.h>
<ctype.h>
<errno.h>
<fenv.h>
<float.h>
<inttypes.h>
<iso646.h>
<limits.h>
<locale.h>
<setjmp.h>
<stdbool.h>
<stddef.h>
<stdint.h>
<tgmath.h>
<wchar.h>
<wctype.h>
– debugging, report assertions which are not true
– character types
– error conditions
– floating point environment
– floating point parameters
– macros for printf
– words for logical operators
– limits of each number type
– international messages
– longjump
– boolean type
– NULL pointer
– portable integer types
– float math functions
– 2-byte characters (unicode)
– 2-byte characters (unicode)
Argument passing between functions
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Arguments are passed on the execution stack
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First temporary variables of the function
Three different argument-passing styles, based on compound types:
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A) pass by value
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int fn ( int & a )
fn ( x )
New symbol ‘a’ labeling old variable, old value is rewritten
Arguments can be used to return multiple values from function
Only variable names can be used as function arguments (not just a value)
This is the FORTRAN method of passing arguments
C) pass by pointer
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fn ( x )
Value of a copied, used to create new variable ‘a’ on the stack
Original variable ‘x’ remains untouched
B) pass by reference
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int fn ( int a )
int fn ( int * a )
fn ( &x )
New pointer variable ‘a’ created on the stack, points to old value of ‘x’
Clunky way of implementing (B)
Arrays are always passed by address only:
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Array type
(pointer)
Double array
(pointer)
int fn ( int v[3] )
int fn ( int * v )
int fn ( int w[][3] )
int fn ( int (*w)[3] )
fn ( v )
fn ( v )
fn ( w )
fn ( w )