1Discussion: October 10, 2007The University of Michigan2Agenda●Questions on anything●Makefiles●GDB●Bit operations3Questions on anything?●Questions?4Makefiles revisitedBasic syntax Target: dependencies [tab] system commandTo run a makefile, simply use: make -f makefilenameBUT, if you simply name your makefile “Makefile”, then you only have to type: make5Makefiles revisited●Suppose we run the following command to compile our program:g++ main.cpp hello.cpp factorial.cpp -o hello●Then we can do the same thing in our makefile by just doing this:all: g++ main.cpp hello.cpp factorial.cpp -o hello●Remember tabs, of course●All is default target for makefiles. That's why it works here.6Makefiles revisited●Why is this so basic compared to before (a.k.a. I hate you, GSI)?7Makefiles revisited●Dependencies are important!●Here is an example makefile for the same source code:all: hellohello: main.o factorial.o hello.o g++ main.o factorial.o hello.o -o hellomain.o: main.cpp g++ -c main.cppfactorial.o: factorial.cpp g++ -c factorial.cpphello.o: hello.cpp g++ -c hello.cppclean: rm -rf *o hello●What advantages does this code have?8Makefiles revisited●Let's look at an example9Makefiles revisited●You can use comments with #●Again, we can have macros:CC=g++CFLAGS=-c -WallLDFLAGS=SOURCES=main.cpp hello.cpp factorial.cppOBJECTS=$(SOURCES:.cpp=.o)EXECUTABLE=helloall: $(SOURCES) $(EXECUTABLE)$(EXECUTABLE): $(OBJECTS) $(CC) $(LDFLAGS) $(OBJECTS) -o [email protected]: $(CC) $(CFLAGS) $< -o $@10Makefiles revisited●If you understand the last example, you can modify it by changing only two lines, no matter what files you have in your project!●Here it is again:CC=g++CFLAGS=-c -WallLDFLAGS=SOURCES=main.cpp hello.cpp factorial.cppOBJECTS=$(SOURCES:.cpp=.o)EXECUTABLE=helloall: $(SOURCES) $(EXECUTABLE)$(EXECUTABLE): $(OBJECTS) $(CC) $(LDFLAGS) $(OBJECTS) -o [email protected]: $(CC) $(CFLAGS) $< -o $@11Makefiles revisited●Questions on makefiles?12GDB revisited●Let's look at an examplekirbyb@myprompt> gdb mainGNU gdb 4.18Copyright 1998 Free Software Foundation, Inc.GDB is free software, covered by the GNU General Public License, and you arewelcome to change it and/or distribute copies of it under certain conditions.Type "show copying" to see the conditions.There is absolutely no warranty for GDB. Type "show warranty" for details.This GDB was configured as "sparc-sun-solaris2.7"...(gdb)●Right now, gdb is just waiting13GDB revisited●Let's say we try to run a program that we've got(gdb) runStarting program: /home/cec/s/a/agg1/.www-docs/tutorial/main Creating Node, 1 are in existence right nowCreating Node, 2 are in existence right nowThe fully created list is:21Now removing elements:Creating Node, 3 are in existence right nowDestroying Node, 2 are in existence right now21(continued on next page)14GDB revisitedProgram received signal SIGSEGV, Segmentation fault.Node<int>::next (this=0x0) at main.cc:2828 Node<T>* next () const { return next_; }(gdb)●Oops, we've got a segfault. What do we do now?●Well, what do we know about the error at this point?–(this)●What do we still want to know?15GDB revisited●It'd be useful to go backwards, and see what values were at places before the error(gdb) backtrace#0 Node<int>::next (this=0x0) at main.cc:28#1 0x2a16c in LinkedList<int>::remove (this=0x40160, item_to_remove=@0xffbef014) at main.cc:77#2 0x1ad10 in main (argc=1, argv=0xffbef0a4) at main.cc:111(gdb)●Ah, now we know a bit more about how we got to the error...●But, how do we figure out what we're trying to remove?16GDB revisited●We can actually take a look at memory addresses!(gdb) x 0xffbef0140xffbef014: 0x00000001(gdb)●This tells us exactly what's in that address!●And how did we know the address was 0xffbef014?17GDB revisited●OK, we can look at memory values, but what about breakpoints again?(gdb) break LinkedList<int>::removeBreakpoint 1 at 0x29fa0: file main.cc, line 52.(gdb)●Here's the classic way to make a breakpoint.–When we do a run with GDB, it will stop here●And conditional breakpoints:(gdb) condition 1 item_to_remove==1(gdb)●This means “only stop at breakpoint 1 if item_to_remove == 1”18GDB revisited●Stepping is also useful. –Simply type “step” to go to the next line, after a breakpoint●And, finally, you can quit gdb by typing “quit”●Use google as a reference for other gdb commands!19Bit operations●Does anyone know what bit operations are?20Bit operations●Bits are fundamental units in computers.●A lot of bit operations simply come down to logic!●Recall truth tables:F ^ F = FT ^ F = FF ^ T = FT ^ T = T●Other examples21Bit operations●Well, we can represent T as 1 and F as 0, and C++ (and C) has equivalent functionality!0 & 0 = 01 & 0 = 00 & 1 = 01 & 1 = 122Bit operations●Bitwise operator meanings:&: binary bitwise AND^: binary bitwise exclusive OR (XOR)| : binary bitwise inclusive OR~ : unary bitwise complement (NOT)●What are the values in the following truth table?0 ^ 0 = ?1 ^ 0 = ?0 ^ 1 = ?1 ^ 1 = ?23Bit operations●Remember not to mix these operators up with standard logical operators.●What is the following pseudo-code-segment doing?if((x==y) & (z!=x))24Bit operations●Does anyone know what bit shifting is?●How is it useful?25Bit operations●What is the value of x after the following code is executed?Int x = 5;int y = 2;x = y << 5;●A useful property of bit shifting! Powers of 2 are cool!●Similarly, you can shift in the other direction with: >>26Questions?Any