g++ -g -Wall -Wwrite-strings -Ddebug main.cc sub.o -o q1Tell what the command name is. Tell what each command line option does. Tell what programs will be run, and what the inputs and outputs of each program will be.
Answer: The command name is g++. The -g option causes the compiler to add information for a debugger to the output files. The -Wall option causes the compiler to print all warning messages. The -Wwrite-strings options causes the compiler to print warning messages if literal strings are not handled as constants. The -Ddebug option defines the symbol "debug" for the preprocessor. The preprocessor will read main.cc, interpret all preprocessor directives and macro references, remove all comments, and write source code to stdout. The compiler will read the output of the preprocessor from stdin, and will write an assembly language program to main.s. The assembler will read main.s and generate main.o. The linker will link main.o, sub.o, and the standard runtime library to produce the executable file, q1. The compiler driver will delete main.s and main.o (but not sub.o).
Answer: Use the mkdir command to create a subdirectory named RCS. Add files to the database using the ci command, providing a description of each file's role in the project when prompted. Use the co command with no options (except the file names) to get read-only copies of files from the database. Use the co command with the -l ("el") option to lock files for editing; that is, to get writeable copies of the files. Use the ci command to enter a new version of a file into the RCS database for a project; provide a log message that tells what changes were made when prompted. Files in the RCS subdirectory have the same names as the files in the project directory, but with ",v" appended to the end of each file name. Files in the database are read-only. They contain housekeeping information, the full text of the most recent version of the file, and a record of all the differences between the current version and each previous version of the file. Use the $Id$ keyword in a comment at the beginning of each file to show the name of the file and its status. Use the $Log$ keyword in the comment block at the beginning of each file to show the history of changes that were made to the file.
A. What is significant about tab characters?
B. Can the make command be used without a Makefile? If not,
explain why not, and if yes, tell when.
C. What is a rule, and what is the difference between an
implicit and an explicit rule? Give an example of both.
D. In the skeleton makefile I provided, there are references to the
symbols CXXFLAGS and OBJS. In what way are these two symbols
similar? What is the significant difference between them?
(Hint: one of them will be used automatically in certain
circumstances, but the other one will never be used
automatically.)
E. The skeleton makefile contains the line,
depend : $(SRCS) $(HDRS).
Tell everything make would do because of this line, assuming the
user types the command, "make depend".
F. What is the difference between the commands, "make depend"
and "makedepend"?
Answer:A. You have to start each command line in a rule with a tab character because make recognizes the end of the command list by seening a line that does not start with a tab character.
B. Yes it can. If you have a single source module, such as myprog.cc, you can type "make myprog" and make will use one of its implicit rules to generate the appropriate command to compile and link the program.
C. A rule consists of a target followed by a colon (:), optionally followed by a list of dependencies on one line. The first line may be followed by any number of command lines, each of which must start with a tab character. An implicit rule is one that is built into make and will be used automatically based on filename endings. An explicit rule is one specified in a Makefile.
D. They are both make variable names. But CXXFLAGS is automatically used by make when it generates compilation commands using its implicit rules, whereas OBJS is used only when written into explicit rules. (It's all right to use CXXFLAGS in explicit rules, too.)
E. It expands the variable SRCS to whatever its value is, which is probably a list of source files. If these files are not already present in the project directory, use an implicit rule to check them out of the RCS database if possible. Then expand HDRS, and if these files are not already present in the project directory, use an implicit rule to check them out of the RCS database if possible.
F. The command "make depend" causes the "depend" rule in the Makefile to be processed (after checking out the Makefile if necessary). The depend rule has a makedepend command in its command list, which gets executed after the dependency part of the rule is processed. The makedepend command updates the Makefile with the header file dependencies for all the .o files that would be generated by compiling all of the source files given as command line arguments to the command.
The program is to read lines from a set of input files whose names are specified on the command line. The input files are assumed to contain lines of text. If an input file cannot be read, print an appropriate error message that includes the file name, and continue on to process the next input file. Exit when all input files have been read.
For each input file, the program is to write a message to an output file that tells the name of the input file and how many lines of text it contained. The default name of the output file is midterm.out, but the user can change this name using the "-o" or "--outfile" command line option (which must be followed by a file name argument). The output file is to be overwritten if it already exists, unless the user specifies the "-a" or "--append" command line option (which takes no argument), in which case messages are to be appended to the file.
If the user specifies "-?" or "--help" on the command line, the program prints a meaningful error message and exits with a status code of 1. Handle invalid command line options in the usual way.
You may write your program as a single source module if you want to. You may implement the entire program in main() if you want to. But you are free to use additional modules and functions if you prefer. Comment your code according to the coding guidelines for this course, except you may reduce the file header(s) and function header(s) to a single summary sentence each. But do include all RCS keywords in the proper places. Do not provide a Makefile.
Answer: See the Coding Solution web page.