Class 42: Files

Held: Tuesday, 19 April 2011

Summary: We explore file input and output.

Related Pages:

• EBoard.
• Lab: Files.
• Reading: K&R 7.5-7.7.

Notes:

• We have an observer today. Ignore it.
• I have responded to your your questions on the files reading.
• I was sorry (and surprised) not to receive questions from DF, DG, JN, EO, KS, and DU.
• Reading for tonight: K&R 6.1-6.5, 6.7.
• Due to prereg and College committee work, I need folks to sign up for appointments. Times at http://www.cs.grinnell.edu/~rebelsky/Schedule/signup.2011S.txt. Signup via email.
• EC for any of the Activism Week activities, e.g., Sarah Smith on Wednesday. [academic]
• EC for Ginsburg convo, Thursday. [academic]
• EC for open discussion with Jane Ginsburg, Thursday, 9:00-10:30 in Mears Cottage. [academic]
• EC for open discussion with Jane Ginsburg, Thursday, 2:30-4:00 in Mears Cottage. [academic]
• EC for Benji's films event Saturday at 4. [peer]
• EC for Spring Bling on Friday. [peer]
• EC for Grinnell Monologues on Friday/Saturday. [peer]
• EC for ISO Cultural evening on Saturday. When else can you watch AG dance? [peer]

Overview:

• Files.
• Files in C.
• Lab.

Files

• Yay! Another basic type.
• Issues:
  • We need persistant storage of data.
  • Most operating systems provide files; it makes sense to be able to write programs that manipulate them.
• C and Unix's contributions:
  • Files are just sequences of bytes.
  • Treat program input and output identically to system input and output.

Files in C

• What do we need for basic types?
  • The type itself.
  • Functions on the type.
• We use FILE * to represent the type.
  • There is underlying information there (just as there are in ints, floats, and the ilk), but you don't need to know it.
• We use fopen (filename, mode) to convert the name of a file to one of these structures.
  • The mode for writing to a file is "w"
  • The mode for reading from a file is "r"
  • The mode for appending to a file is "a"
  • There are other more complicated options.
• We use fclose to tell the operating system that we're done using a file.
• We use fgetc (char), fgets (string), and fscanf (general) to read from a file.
• We use fputc (char), fputs (string), and fprintf (general) to write to a file.
• stdout, stdin, and stderr are pseudo-files - you can treat them just like files, except you don't use fopen and fclose.
• ferror checks if something is wrong with a file.

Lab

• Do the lab.
• Be prepared to discuss how to do unit testing with the program.