A Version of the Standard Linux cat CommandΒΆ
This version of the cat
command has at least two major bugs! See
mycat_fixed.cpp for a fixed version.
// mycat_2bugs.cpp
//////////////////////////////////////////////////////////////////////////////////////////
//
// This is a simple version of the standard Linux command "cat", that is used
// for displaying the contents of files at the command-line.
//
// You can use cat like this:
//
// $ cat makefile
// CPPFLAGS = -std=c++14 -Wall -Wextra -Werror -Wfatal-errors -Wno-sign-compare -Wnon-virtual-dtor -g
//
// cat has a few options, such as:
//
// - -E puts a $ character at the end of each line
//
// - -n numbers the lines
//
// - -T shows tab characters as ^I
//
// The version of cat we create here won't any flags as iput, but will have
// all of these options turned on by default.
//
// Note that for printing line numbers the C function printf is used. This is
// for simplicity, since it is easier to create a right-justified number using
// printf than using cout. You can certainly do it with cout, but it is more
// complicated and requires more code.
//
// printf requires C-style strings as input, and so when want to use C++-style
// strings (i.e. from #include stirng>) we call the s.c_str().
//
//////////////////////////////////////////////////////////////////////////////////////////
#include "cmpt_error.h"
#include <iostream> // cout
#include <fstream> // ifstream
#include <cstdio> // printf
#include <string>
using namespace std;
//
// useful constants
//
const bool DEBUG_ON = false;
const string TAB_PRINT = "^I";
const string NEWLINE_PRINT = "$";
const string NUM_FORMAT = "%6d "; // right-justified in a 6 char wide field
//
// We're reading arguments from the command-line, and so we use this
// old-fashioned C-style way of dealing with strings and arrays.
//
// argc: the argument count
//
// argv: an array of C-style strings contain all the arguments;
// the first argument is the program name
int main(int argc, char *argv[]) {
if (DEBUG_ON) {
// print all arguments
cout << argc << " arguments:\n";
for(int i = 0; i < argc; i++) {
cout << " arg[" << i << "] = \"" << argv[i] << "\"\n";
}
}
//
// make sure a file argument has been provided
//
// first argument to mycat will be the file we want to display
if (argc < 2) {
cout << "Error: not enough arguments\n";
exit(-1); // -1 could be used by programs that call this program as an
} // error code
//
// try opening the file
//
ifstream infile(argv[1]); // not argv[0] (argv[0] is the name of the program)
if (infile.fail()) {
cout << "Error: unable to open file " << argv[1] << "\n";
exit(-1);
}
//
// read the input file one character at a time
//
int line_num = 0;
char c;
infile.get(c);
// start of file is handled as a special case
if (!infile.eof()) {
line_num++;
printf(NUM_FORMAT.c_str(), line_num);
cout << c;
infile.get(c);
}
while (!infile.eof()) {
switch (c) {
case '\n': // \n is the newline character
cout << NEWLINE_PRINT << "\n";
line_num++;
printf(NUM_FORMAT.c_str(), line_num);
break;
case '\t': // \t is the tab character
cout << TAB_PRINT;
break;
default:
cout << c;
} // switch
infile.get(c);
} // while
} // main