2.13. File I/O

  • Objective: Read and write to/from files like what we have done from the terminal.

  • Need to open a file, perform I/O, and then close the file.

  • To do this we need the notion of a file descriptor, which is our means of accessing the file.

  • The file descriptor is a pointer of type (FILE *), which is a pointer to a data structure. See File I/O for more information.

  • fopen("filename", "[rw]") is the function we will use for opening files. See fopen modes for more information.

  • With an open file, we can use fscanf(), fprintf(), fgets() and other file I/0 functions.

  • We use fclose( FILE * ) to close an open file.

  • Don’t worry if you find this confusing at this time. We will cover file I/O in much more detail later.

2.13.1. File I/O examples

FILE *fin, *fout;
char buff[SIZE];

fin = fopen( "filename", "r" ); /* filename could be supplied by a
                                   string instead of a constant. */
fout = fopen( "filename", "w" );

fgets( buff, SIZE, fin );
fscanf( fin, "format", ...);

fprintf( fout, "format", ...);

fclose(fin);
fclose(fout);

Now complete Homework 5 - Mean and Standard Deviation of Numbers.