1 DOS vs. UNIX files Ending lines with “\r\n” vs. “\n” Reading an entire line at a time getline() To skip white space or not cin >> ch; vs. ch = cin.get(); Command line args, again Examples & Demos CSE Lecture 9 – Files & More

2 Rest of the week Introduction to functions & prototypes Function parameters (formal and actual) Value and reference parameters Recursion Template functions Curses I/O Text based windowing function library Read: Sections

3 DOS vs. UNIX Files In DOS ASCII Text Files All lines end withTWO characters or “\r\n” In UNIX ASCII Text Files All lines end with ONE character or ‘\n’ Converting between two in UNIX/Linux dos2unix – converts dos files to UNIX format unix2dos – converts unix files to DOS format

4 DOS vs. UNIX Files How will you know? Open a DOS text file in some UNIX editors like “vi” and you will see a ‘^M’ character at the end of each line These are the ‘\r’ or return characters Open a UNIX text file using a DOS/Windows editor like “notepad” and the whole file appears to be on one line This is because of the missing ‘\r’ characters

5 Reading an entire line To read an entire line at once … Declare a string variable string lineIn; Use getline() to read the whole line from cin getline(cin, lineIn); Or read the whole line from an istream getline(inFile, lineIn);

6 Reading until a given char … You can even read all of the line up to a specific character … To read up to the next period getline(cin, lineIn, ‘.’);

7 Getline() cautions There is another version of getline() that is defined in the istream class and which uses char arrays as input buffers Its arguments are A char array, a limit number, a limit char (‘\n’ by default) It is called like this char buffer[100]; cin.getline(buffer, 100); infile.getline(buffer, 100, ‘.’)

8 Command line args, again … The command line is broken up by white space argc is the count of strings on the command line argv is an indexed list (an array) of strings, from the command line, beginning with the name of the program

9 Sample Program - comline // comline.cpp – JHS // Usage: comline.... #include using namespace std; int main (int argc, char *argv[]) { cout << “Program run w/ following command line.\n"; for (int i=0; i<argc; i++) cout << ' ' << argv[i]; cout << endl; cout << "Command line arguments are...\n"; cout << "argc = " << argc << endl; for (int i=0; i<argc; i++) cout << "argv[" << i << "] " << argv[i] << endl; return 0; }

10 Skipping White Space By default, the input stream extractions (>>) are separated by white space, so this gets the next character that is NOT white space cin >> ch; The get() function gets the next character no matter what it is (whitespace or not) ch = cin.get(); Use what is appropriate See cat.cpp vs. cat2.cpp for difference

11 Demo Programs tocaps (using the (char) cast) tocaps_oops (failing to use the (char) cast) disks (C-style I/O) more2 (uses getline) cat vs. cat2 (ch=cin.get(); vs. cin >> ch;) cat vs../cat (path issues, what gets run)

12 ToCaps … Another use of argc & argv // File: tocaps.cpp - JHS(9/14/2003) // Purpose: // Shows file contents on screen (IN ALL CAPS). // File specified by command line argument. // Discussion: // Demo of loops, file streams, & args to main. // Usage: tocaps #include #include <cctype using namespace std; int main (int argc, char *argv[]) { char charIn; ifstream infile;

13 ToCaps … Another use of argc & argv // do we have a correct command line with filename? if (argc != 2) { cout \n"; exit(1); } // use filename to open file for input // note: argv[0] is the command name “tocaps" // argv[1] is the filename from the command line infile.open(argv[1]); if (infile.fail()) { cout << "File failed to open!" << endl; exit(2); }

14 ToCaps … Another use of argc & argv // loop gets characters one at a time until // end of file is found while ((charIn = infile.get()) != EOF) { if (isalpha(charIn)) // echo upper case equivalent of letter cout << (char)toupper(charIn); //cout << toupper(charIn); in “tocaps_oops.cpp” else // echo other character to screen cout << charIn; } infile.close(); return 0; }

15 Disks … Final example using C-style I/O Program computes the volumes of a sequence of disks and outputs a summary report. A file contains lines of data. Each line describes a number and size of disks of a certain type. Line Format: number(int) diameter(float) thickness(float) type(char) Examples: A G Last line is the sentinel line q

16 Sample “diskdata.txt” File A F R V q

17 Sample run of./disks >./disks diskdata.txt results.txt 3 disks of type A : volume = disks of type F : volume = disks of type R : volume = disks of type V : volume = Total volume of all disks = >

18 Disks.c /* ********************************************************* ** disks.c - JHS 06 (C-style I/O & computing disk volume) ********************************************************* */ #include #define PI int main(int argc, char *argv[]) { FILE *infile, *outfile; int num; float radius, diameter, thickness, volume, total; char type; total = 0.0;

19 Disks.c if (argc != 3) { printf("Usage: disks \n"); return 1; } infile = fopen(argv[1],"r"); if (NULL == infile) { printf("Cannot open input file!\n"); return 2; } outfile = fopen(argv[2],"w"); if (NULL == outfile) { printf("Cannot create output file!\n"); return 3; }

20 Disks.c fscanf(infile,"%d %f %f %c", &num, &diameter, &thickness, &type); while (type != 'q') // while sentinel has not been read { radius = 0.5*diameter; volume = num*(PI*radius*radius*thickness); total = total + volume; /* show the user */ printf("%4d disks of type %c : volume = %10.3f\n", num, type, volume); /* output same information to disk */ fprintf(outfile, "%4d disks of type %c : volume = %10.3f\n", num, type, volume); /* read another line */ fscanf(infile,"%d %f %f %c", &num, &diameter, &thickness, &type); }

21 Disks.c printf("Total volume of all disks = %10.3f\n", total); fprintf(outfile,"Total volume of all disks = %10.3f\n", total); fclose(infile); fclose(outfile); return 0; }

22 Program “cat.cpp” // cat.cpp – JHS 2006 // NOTE: This skips all white space & compresses text // Usage: cat #include using namespace std; int main (int argc, char *argv[]) { char charIn; ifstream infile; // do we have a correct command line with filename? if (argc != 2) { cout \n"; exit(1); }

23 Program “cat.cpp” // use filename to open file for input // argv[1] is the filename from the command line infile.open(argv[1]); if (infile.fail()) { cout << "File failed to open!" << endl; exit(2); } // get characters one at a time until end of file found infile >> charIn; // get 1st non whitespace character while (!infile.eof()) { cout << charIn; // echo character to screen infile >> charIn; // get next non whitespace character } infile.close(); return 0; }

24 Program “cat2.cpp” // cat2.cpp – JHS 2006 // NOTE: This reads and displays ALL text, even whitespace // Usage: cat2 #include using namespace std; int main (int argc, char *argv[]) { char charIn; ifstream infile; // do we have a correct command line with filename? if (argc != 2) { cout \n"; exit(1); }

25 Program “cat2.cpp” // use filename to open file for input // argv[1] is the filename from the command line infile.open(argv[1]); if (infile.fail()) { cout << "File failed to open!" << endl; exit(2); } // get characters one at a time until end of file found while ((charIn = infile.get()) != EOF) // get char & test { cout << charIn; // echo character to screen } infile.close(); return 0; }

26 Program – more2.cpp // more2.cpp – JHS 2006 // This program shows a file contents on the screen // (one page at a time), using getline() // Usage: more2 #include using namespace std; int main (int argc, char *argv[]) { string lineIn; ifstream infile; int lines; // number of lines shown before pause bool quit; char resp;

27 Program – more2.cpp // do we have a correct command line with filename? if (argc != 2) { cout \n"; exit(1); } // use filename to open file for input // argv[1] is the filename from the command line infile.open(argv[1]); if (infile.fail()) { cout << "File failed to open!" << endl; exit(2); } // get lines of text until end of file found lines = 0; quit = false; getline(infile,lineIn); // get first line

28 Program – more2.cpp while ((!infile.eof()) && (!quit)) { // NOTE: getline consumes the ‘\n’ at end of each line // but it is not made part of string. cout << lineIn << endl; // echo text line to screen lines++; if (lines > 24) { resp = cin.get(); if (resp == 'q') quit = true; // set flag so program quits else lines = 0; // reset line count } getline(infile,lineIn); // get next line of text } infile.close(); return 0; }

29 Path issues – what gets executed? Your bash shell in Linux is the command interpreter It’s environment can be displayed using set and env One of the variables is path or PATH The order of directories in the path determines which version of a command or program gets run when you type its name Typing a command this way./prog tells the shell to look in the current directory for prog rather than searching the path

30 Path issues – what gets executed? Example There is a Linux command “disks” and we have a program called “disks” Type disks and the Linux command is run > disks disks: you must be root to run this program Type./disks and our program is run >./disks Usage: disks Try cat &./cat to see the difference between the Linux cat and ours.