Hank Childs, University of Oregon

CIS 330: _ _ _ _ ______ _ _____ / / / /___ (_) __ ____ _____ ____/ / / ____/ _/_/ ____/__ __ / / / / __ \/ / |/_/ / __ `/ __ \/ __ / / / _/_// / __/ /___/ /_ / /_/ / / /…

CIS 330: _ _ _ _ ______ _ _____ / / / /___ (_) __ ____ _____ ____/ / / ____/ _/_/ ____/__ __ / / / / __ \/ / |/_/ / __ `/ __ \/ __ / / / _/_// / __/ /___/ /_ / /_/ / / / / /> < / /_/ / / / / /_/ / / /____/_/ / /__/_ __/_ __/ \____/_/ /_/_/_/|_| \__,_/_/ /_/\__,_/ \____/_/ \____//_/ /_/ Lecture 8:Building Large Projects,Mangling and NamespacesBeginning on Project 3Hank Childs, University of OregonApril 25th, 2014Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Schedule changes for this week

Lecture #8: right now

Lecture #9: Friday 10-11, 11-12, and 3:30-4:30

We will do Proj2N for lecture #9

No lecture on May 9th

(we are banking an extra this week)

Proj 2D: graded in class today

Proj 2C: due Monday

Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Memory Addresses

Every location in memory has an address associated with it

Locations in memory are represented in hexadecimal

CodeDataStack0x7fff55bc0x7fff55b8FreeHeapMemory addresses descend in the stack, ascend in the heap.Pointers

Pointers store locations in memory

“&”: unary operator that gives the address of a variable.

int x;int *yp = &x;‘*’ operator

Let “ptr” be a pointer

Then “*ptr” returns value in the address that ptr points to.

* = “dereference operator”

Pointer Arithmetic

You can combine pointers and integers to get new pointer locations

ptr + 1ptr + sizeof(type) bytesArrays

Arrays: container that has multiple elements of identical type, all stored in contiguous memory

int A[10]; 10 integers, stored in 40 consecutive bytes (assuming sizeof(int) == 4)Arrays are just pointers. You can use arrays and pointers interchangeably.[ ] operator

[ ] is a way of dereferencing memory

Recall that ‘*’ is the dereference operator

A[0] <= => *A

A[5] <= => *(A+5);

Pointers to pointers

Remember: pointer points to a location in memory

We’ve been considering cases where locations in memory are arrays of integers

But locations in memory could be pointer themselves

CodeDataStack0x7fff55bc0x7fff55b8FreeHeapCall by reference / call by value

Refers to how parameters are passed to a function.

Call by reference: send a reference (pointer) as a function parameter

Side effects in that function affect the variable in the calling function

Call by value: send the value of the variable as a function parameter

Side effects in that function don’t affect the variable in the calling function

Questions?

Something unclear from last time?

Questions about HW?

vi tips?

Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

3 files: prototypes.h, rectangle.c, driver.cprototypes.hstructRectangle;void IntializeRectangle(struct Rectangle *r, double v1, double v2, double v3, double v4);rectangle.cstruct Rectangle{ double minX, maxX, minY, maxY;};void IntializeRectangle(struct Rectangle *r, double v1, double v2, double v3, double v4){ r->minX = v1;r->maxX = v2; r->minY = v3; r->maxY = v4;}driver.c#include <prototypes.h>int main(){struct Rectangle r; InitializeRectangle(r, 0, 1, 0, 1.5);}Review on compilation

gcc –c: build an object file (.o), i.e., binary code that can directly run on the architecture

Then the binary can be generated from the object files.

Libraries are a mechanism for grouping up a bunch of related object files

They are assembled together using a program called an archiver (ar)

You can also just use object files directly when linking.

Makefiles

Consists of rules

Rule syntax:

target: dependency1 dep2 … depN<tab>command1<tab>command2Quiz: write down a Makefile for a program called proj2B. Again, the file names are prototypes.h, driver.c, rectangle.cMakefile for prototypes.h, rectangle.c, driver.cMakefileproj2B: driver.crectangle.cprototypes.hgcc -I. -c rectangle.cgcc -I. -c driver.cgcc -o proj2B driver.orectangle.oIs this a good Makefile?What’s the problem with it?Makefile for prototypes.h, rectangle.c, driver.cMakefileproj2B: rectangle.odriver.ogcc -o proj2B driver.orectangle.odriver.o: prototypes.hdriver.cgcc -I. -c driver.crectangle.o: prototypes.hrectangle.cgcc -I. -c rectangle.cDefinition of Rectangle in rectangle.cWhy is this a problem?prototypes.hstructRectangle;void IntializeRectangle(struct Rectangle *r, double v1, double v2, double v3, double v4);rectangle.cstruct Rectangle{ double minX, maxX, minY, maxY;};void IntializeRectangle(struct Rectangle *r, double v1, double v2, double v3, double v4){ r->minX = v1;r->maxX = v2; r->minY = v3; r->maxY = v4;}“gcc –c driver.c” needs to make an object file. It needs info about Rectangle then, not later.driver.c#include <prototypes.h>int main(){struct Rectangle r; InitializeRectangle(r, 0, 1, 0, 1.5);}New gcc option: “gcc –E”The fix is to make sure driver.c has access to the Rectangle struct definition.driver.c#include <prototypes.h>int main(){struct Rectangle r; InitializeRectangle(r, 0, 1, 0, 1.5);}gcc –E shows what the compiler sees after satisfying “preprocessing”, which includes steps like “#include”.# 1 "driver.c"# 1 "<built-in>" 1# 1 "<built-in>" 3# 162 "<built-in>" 3# 1 "<command line>" 1# 1 "<built-in>" 2# 1 "driver.c" 2# 1 "./prototypes.h" 1structRectangle;voidInitializeRectangle(structRectangle *r, double v1, double v2, double v3, double v4);# 2 "driver.c" 2intmain(){structRectangle r;InitializeRectangle(r, 0, 1, 0, 1.5);}gcc–E –I. driver.cThis is it. If the compiler can’t figure out how to make object file with this, then it has to give up.Preprocessor

Preprocessor:

takes an input program

produces another program (which is then compiled)

C has a separate language for preprocessing

Different syntax than C

Uses macros (“#”)

macro (“macroinstruction”): rule for replacing input characters with output charactersPreprocessor Phases

Resolve #includes

(we understand #include phase)

Conditional compilation

Macro replacement

Special macros

#define compilationThis is an example of macro replacement.#define via gcc command-line optionConflicting –D and #defineConditional compilationConditional compilation controlled via compiler flagsThis is how configure/cmake controls the compilation.4 files: struct.h, prototypes.h, rectangle.c, driver.cstruct.hstruct Rectangle{ double minX, maxX, minY, maxY;};prototypes.h#include <struct.h>void InitializeRectangle(struct Rectangle *r, double v1, double v2, double v3, double v4);rectangle.c#include <struct.h>#include <prototypes.h>void IntializeRectangle(struct Rectangle *r, double v1, double v2, double v3, double v4){ r->minX = v1;r->maxX = v2; r->minY = v3; r->maxY = v4;}#include <struct.h>#include <prototypes.h>int main(){struct Rectangle r; InitializeRectangle(&r, 0, 1, 0, 1.5);}driver.cWhat is the problem with this configuration?Compilation errorgcc –E rectangle.c#ifndef/ #define to the rescuestruct.h#ifndef RECTANGLE_330#define RECTANGLE_330struct Rectangle{ double minX, maxX, minY, maxY;};#endifWhy does this work?This problem comes up a lot with big projects, and especially with C++.There is more to macros…

Macros are powerful & can be used to generate custom code.

Beyond what we will do here.

Two special macros that are useful:

__FILE__ and __LINE__

Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Problem with C…Problem with C…No checking of type…Problem is fixed with C++…Problem is fixed with C++…Mangling

Mangling refers to combing information about arguments and “mangling” it with function name.

Way of ensuring that you don’t mix up functions.

Why not return type too?

Causes problems with compiler mismatches

C++ compilers haven’t standardized.

Can’t take library from icpc and combine it with g++.

C++ will let you overload functions with different typesC++ also gives you access to mangling via “namespaces”Functions or variables within a namespace are accessed with “::”C++ also gives you access to mangling via “namespaces”The “using” keyword makes all functions and variables from a namespace available without needing “::”. And you can still access other namespaces.Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Project #3A: background

Definitions:

Image: 2D array of pixels

Pixel: A minute area of illumination on a display screen, one of many from which an image is composed.

Pixels are made up of three colors: Red, Green, Blue (RGB)

Amount of each color scored from 0 to 1

100% Red + 100% Green + 0% Blue = Yellow

100% Red + 0% Green + 100 %Blue = Purple

0% Red + 100% Green + 0% Blue = Cyan

100% Red + 100% Blue + 100% Green = White

Project #3A: background

Colors are 0->1, but how much resolution is needed? How many bits should you use to represent the color?

Can your eye tell the difference between 8 bits and 32 bits?

 No. Human eye can distinguish ~10M colors.

8bits * 3 colors = 24 bits = ~16M colors.

Red = (255,0,0)

Green = (0,255,0)

Blue = (0,0,255)

Project 3A

Prompt posted by Saturday night

Due on Friday, May 2nd

Tasks:

Struct to contain image

Read image from file (simplified format)

Write image to file (simplified format)

Function to modify image

Program that puts it all together

We will be modifying this code throughout the quarter… (expect you will have to retrofit what you are writing now)Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Memory Errors

Array bounds read

Array bounds write

Memory Errors

Free memory read / free memory write

When does this happen in real-world scenarios?Memory Errors

Freeing unallocated memory

When does this happen in real-world scenarios?Vocabulary: “dangling pointer”: pointer that points to memory that has already been freed.Memory Errors

Freeing non-heap memory

When does this happen in real-world scenarios?Memory Errors

NULL pointer read / write

NULL is never a valid location to read from or write to, and accessing them results in a “segmentation fault”

…. remember those memory segments?

When does this happen in real-world scenarios?Memory Errors

Unitialized memory read

When does this happen in real-world scenarios?Outline

Announcements/Review

Grade project 2D

Building Large Projects

Mangling with C/C++

Project 3A

Background on images

Bonus topics

Memory Errors

Webpages

Web pages

ssh –l <user name> ix.cs.uoregon.edu

cd public_html

put something in index.html

 it will show up as

http://ix.cs.uoregon.edu/~<username>Web pages

You can also exchange files this way

scpfile.pdf <username>@ix.cs.uoregon.edu:~/public_html

point people to http://ix.cs.uoregon.edu/~<username>/file.pdf

Note that ~/public_html/dir1shows up as http://ix.cs.uoregon.edu/~<username>/dir1(“~/dir1” is not accessible via web)