{small lecturenumber - hepage :} Working with files{small lecturenumber - hepage :} Opening files for reading{small lecturenumber - hepage :} Opening files for reading{small lecturenumber - hepage :} Reading from a file{small lecturenumber - hepage :} Example: cat{small lecturenumber - hepage :} Using assignments as tests{small lecturenumber - hepage :} Exercise 1: file reading{small lecturenumber - hepage :} Working with command line arguments{small lecturenumber - hepage :} Working with command line arguments{small lecturenumber - hepage :} Exercise 2{small lecturenumber - hepage :} Writing to files{small lecturenumber - hepage :} Exercise 3{small lecturenumber - hepage :} Converting strings to ints{small lecturenumber - hepage :} Exercise 4{small lecturenumber - hepage :} Project 5Intro to Programming IIFilesChris BrooksDepartment of Computer ScienceUniversity of San FranciscoDepartment of Computer Science — University of San Francisco – p. 1/??23-2: Working with files•In C, you work with files by accessing a file pointer.•This is declared like this:#include <stdio.h>...FILE*fptr;(notice the caps)Department of Computer Science — University of San Francisco – p. 2/??23-3: Opening files for reading•fopen() opens a file and returns a file pointer.•It takes two arguments:◦The file name◦A string indicating whether we’re opening for reading orwriting.Department of Computer Science — University of San Francisco – p. 3/??23-4: Opening files for reading•For exampleFILE*fp = fopen("myfile","r");opens myfile for reading.Department of Computer Science — University of San Francisco – p. 4/??23-5: Reading from a file•fscanf is used to read from a file.•Works exactly like scanf, except that the first argument is thefile pointer.•You can also use getc - it returns the integer representing thenext character in the file.•getc() returns EOF if you’re at the end of the file.Department of Computer Science — University of San Francisco – p. 5/??23-6: Example: cat•Let’s say we wanted to write a program to display the contentsof a file to the screen.◦In Unix. this program is called ’cat’.•How might we go about this?Department of Computer Science — University of San Francisco – p. 6/??23-7: Using assignments as tests•One shortcut you can do in C:◦(This is not legal in Java)•In C, when you assign a value to a variable, you can use if andwhile to check the result of that assignment.•So, you often see folks do this:while ((c = getc(fp)) != EOF) {printf("%c",c);}Department of Computer Science — University of San Francisco – p. 7/??23-8: Exercise 1: file reading•Take the ’cat’ program we just talked about and modify it asfollows:◦Have it open two files and read them each character bycharacter.◦If the files are the same, print ’true’.◦Otherwise, print ’false’.Department of Computer Science — University of San Francisco – p. 8/??23-9: Working with command line arguments•We’d like to make our program a little more general.◦It’s pretty irritating to have to recompile every time we wantto cat a different file.•Let’s provide the filename as a command line argument•For example: mycat file1 file2Department of Computer Science — University of San Francisco – p. 9/??23-10: Working with command line arguments•To do this, we need to specify that main() will receivearguments.◦Remember, main is just another function.•It takes its arguments in a special form:intmain(int argc, char**argv)•argc is the number of command line arguments•argv is an array of strings, one for each argument.•argv[0] is the name of the program.Department of Computer Science — University of San Francisco – p. 10/??23-11: Exercise 2•Modify cat to:◦Take two file names as arguments.◦Check to make sure argc >= 3.Department of Computer Science — University of San Francisco – p. 11/??23-12: Writing to files•To open a file for writing, use the "w" argument to fopen.fopen("foo","w");•You can then write to a file with:◦fprintf(FILE *fp, char *stringToPrint, arg1, arg2 ...)◦putc(FILE *fp, int c)Department of Computer Science — University of San Francisco – p. 12/??23-13: Exercise 3•Modify cat to read in the file indicated by the first argument andwrite it out to the file indicated by the second argument.Department of Computer Science — University of San Francisco – p. 13/??23-14: Converting strings to ints•What if you need to convert a string to an integer?◦Say you want to provide an integer as a command lineargument?•atoi(char *s) will return an integer representation of the string s.Department of Computer Science — University of San Francisco – p. 14/??23-15: Exercise 4•Modify the multiplication program from Wednesday to takethree command line arguments:◦The number of rows◦The number of columns◦A file to write the table to.Department of Computer Science — University of San Francisco – p. 15/??23-16: Project 5•You should now have the necessary tools to do the followingparts of project 5:◦createRandomBoard()◦readBoardFromFile()◦printBoard()◦getAliveNeighbors()◦isValidCell()◦updateBoard()◦main•I’d suggest starting with createRandom board, readBoardFromFile, and printBoard. Then start on your main, so that you cantest each of these.Department of Computer Science — University of San Francisco – p.
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