All example C++ code (e.g., from recorded lectures) makes use of makefiles. You will use makefiles in each C++ assignment. Makefiles are used to perform compilation and linking steps. For C++, this takes the form of:

1. Compiling C++ implementation files (e.g., .cpp, .cc, .cxx) to *.o files.
2. Linking .o files to create one or more executables (binaries).

Writing a makefile is an exercise best left to CS 252 (Introduction to Unix/Linux) or an equivalent course. You are required to use makefiles in this course.

MAINPROG=cmd_line_example

SOURCES:=$(wildcard *.cpp)
OBJECTS=$(SOURCES:.cpp=.o)
FLAGS=-std=c++17 -fsanitize=leak,address -Wall -Wpedantic -fuse-ld=gold

all: $(SOURCES) $(MAINPROG)

$(MAINPROG): $(OBJECTS)
	g++ $(FLAGS) $(OBJECTS) -o $@

.cpp.o:
	g++ $(FLAGS) -c $< -o $@

clean:
	rm *.o $(MAINPROG)

Let us break everything down…

MAINPROG=cmd_line_example

The first line is a variable. It is used to specify the name for the final executable. In this example, the final executable will be named cmd_line_example.

SOURCES:=$(wildcard *.cpp)
OBJECTS=$(SOURCES:.cpp=.o)

The SOURCES line uses a wild card (i.e., .cpp) to grab a list of all cpp files in the current directory. The OBJECTS line constructs a list of .o files that need to be compiled (one per cpp file).

FLAGS=-std=c++17 -fsanitize=leak,address -Wall -Wpedantic -fuse-ld=gold

The FLAGS line specifies what compilation flags need to be used:

• -std=c++17 - use the C++17 standard (this could also be c++0x, c++11, c++14, or c++2a depending on compiler).

• -fsanitize=leak,address - add memory leak checks and a few other address checks, generating a report if any are encountered during program execution.

• -Wall - enable warning for potential issues (e.g., comparing signed and unsigned numbers).

• -Wpedantic - enable even more warnings (This is essentially… ALL THE WARNINGS).

• -fuse-ld=gold - this is required due to a linker bug on Ubuntu Linux and certain version of g++.

all: $(SOURCES) $(MAINPROG)

When make or make all is run, compile everything (all cpp files) and build the main program.

$(MAINPROG): $(OBJECTS)
	g++ $(FLAGS) $(OBJECTS) -o $@

.cpp.o:
	g++ $(FLAGS) -c $< -o $@

This is a meta-rule that tells the makefile how to compile each cpp file.

clean:
	rm *.o $(MAINPROG)

When make clean is run, delete all .o files and delete the final executable.

#include <iostream>
#include <iomanip>

using namespace std;

/**
 * Echo all command line arguments, one per line in the form:
 *
 *   idx: arg
 *
 * where idx is the index (0, 1, ...) and arg is the argument.
 *
 * @param argc number of arguments
 * @param argv 2D array of C-style (null terminated) strings
 * @param outs output destination (e.g., cerr or cout)
 */
void echo_arguments(const int argc, char** argv, ostream& outs=std::cerr)
{
    // There is always at least one argument, i.e., the program name
    outs << right << setw(3) << 0 << ": " << argv[0] << "\n";
    outs << "\n";

    for (int i = 1; i < argc; i++) {
        // Technically "right" does not need to be repeated, but
        // we would probably tweak formatting more in the future
        outs << right << setw(3) << i << ": " << argv[i] << "\n";
    }
}

int main(int argc, char** argv)
{
    echo_arguments(argc, argv);

    return 0;
}

cmd_line_ex.cpp is a simple program. All it does is echo any entered command line arguments using the echo_arguments function.

void echo_arguments(const int argc, char** argv, ostream& outs=std::cerr)
{
    // There is always at least one argument, i.e., the program name
    outs << right << setw(3) << 0 << ": " << argv[0] << "\n";
    outs << "\n";

    for (int i = 1; i < argc; i++) {
        // Technically "right" does not need to be repeated, but
        // we would probably tweak formatting more in the future
        outs << right << setw(3) << i << ": " << argv[i] << "\n";
    }
}

The first argument (i.e., argv[0]) is a special case. It is always the program name, and it is supplied automatically.

MAINPROG=cmd_line_example

SOURCES:=$(wildcard *.cpp)
OBJECTS=$(SOURCES:.cpp=.o)
FLAGS=-std=c++17 -fsanitize=leak,address -Wall -Wpedantic -fuse-ld=gold

all: $(SOURCES) $(MAINPROG)

$(MAINPROG): $(OBJECTS)
	g++ $(FLAGS) $(OBJECTS) -o $@

.cpp.o:
	g++ $(FLAGS) -c $< -o $@

clean:
	rm *.o $(MAINPROG)

and

#include <iostream>
#include <iomanip>

using namespace std;

/**
 * Echo all command line arguments, one per line in the form:
 *
 *   idx: arg
 *
 * where idx is the index (0, 1, ...) and arg is the argument.
 *
 * @param argc number of arguments
 * @param argv 2D array of C-style (null terminated) strings
 * @param outs output destination (e.g., cerr or cout)
 */
void echo_arguments(const int argc, char** argv, ostream& outs=std::cerr)
{
    // There is always at least one argument, i.e., the program name
    outs << right << setw(3) << 0 << ": " << argv[0] << "\n";
    outs << "\n";

    for (int i = 1; i < argc; i++) {
        // Technically "right" does not need to be repeated, but
        // we would probably tweak formatting more in the future
        outs << right << setw(3) << i << ": " << argv[i] << "\n";
    }
}

int main(int argc, char** argv)
{
    echo_arguments(argc, argv);

    return 0;
}

..then open a Linux terminal (e.g., SSH into a CS Linux server or open a local Linux terminal). Run make to compile cmd_line_ex.cpp.

1. Run ./cmd_line_example

   You should see…

     0: ./cmd_line_example
   

2. Run ./cmd_line_example 1 2 77 The letter Q "Hello, and..."

   You should see…

     0: ./cmd_line_example
   
     1: 1
     2: 2
     3: 77
     4: The
     5: letter
     6: Q
     7: Hello, and...!
   

Do not forget… The double quotes are required for any argument that contains spaces.

    if (argc < 2) {
        cout << "No input file provided." << "\n";
        cout << "Usage: " << argv[0] << " input_file" << "\n";
        return 1;
    }

    ifstream shapesFile(argv[1]);

    if (!shapesFile) {
        cout << "Error: " << argv[1] << "could not be opened" << "\n";
        return 2;
    }

    if (argc < 2) {