1. Files A collection of related data treated as a unit. Two types Text
Binary
Stored in secondary storage devices.
Buffer
Temporary storage area that holds data while they are being transferred to or from memory.

2. Text Files Data are stored as human-readable characters
Each line of data ends with a newline character

3. Standard Files Standard input Associated with the keyboard
Accessed using stdin
Standard output
Associated with the monitor
Accessed using stdout
Standard error
Accessed using stderr

4. User Files External files defined by the user
Must be explicitly opened in the program.
C assigns a logical name to each external file.
fopen function
Prepares a file for processing
Makes the connection between the external file and the program
Creates a program file table or control structure to store the information needed to process the file

5. fopen FILE * fopen(char * filename, char * mode)
filename – string that supplies the name of the file as known to the external world. e.g. scores.dat
mode
Meaning r
Open file for reading
If file exists, the marker is positioned at beginning.
If file does not exist, error returned w
Open text file for writing
If file exists, it is emptied.
If file does not exist, it is created. a
Open text file for append.
If file exists, the marker is positioned at the end.

6. Examples

7. fopen If succesful, will return a pointer to a FILE object
If not, a null pointer is returned
Always check to make sure the open was successful. If not, print an error message and exit
Example:

8. fclose int fclose(FILE *fp) Used to close a file when no longer needed
Prevents associated file from being accessed again
Guarantees that data stored in the stream buffer is written to the file
Releases the FILE structure so that it can be used with another file
Frees system resources, such as buffer space
Returns zero on success, or EOF on failure

9. fclose
Examples:

10. Formatted Input Functions
Read and convert a stream of characters and store the converted values in a list of variables found in the address list
scanf
scanf ("format string", address list);
Reads text data from standard input
fscanf
fscanf(fp, "format string", address list);
Reads input from the specified file

11. Formatted Output Functions
Displays output in human readable form
printf
printf ("format string", value list);
Writes to standard output or standard error file
fprintf
fprintf (fp, "format string", value list);
Writes to the specified file.

12. Formatting Input/Output Functions
Format strings
Consist of three types of data
Whitespace
Text characters
Field specification
These may be repeated

13. Field Specification
Consists of % character, a conversion code, and other formatting instructions
With one exception (*), each field specification must have a matching parameter in the parameter list that follows the string
The type in the field specification and the type of the parameter must match
Can have up to six elements for output
Can have up to five elements for input; precision is not allowed

14. Field Specification Elements of field specification scanf / fscanf:%
flag
Max width
size
conversion code
* do not store data
h short
l long int
l double (scan only)
L long double
left justify
+ sign (+ or -)
space if positive
0 zero padding
d, f, c, s, e, E, x, X, i, u, g, G %
flag
Max width
precision
size
conversion code
printf / fprintf

15. Field Specification
Examples %d
%7d
%+d
%lf
%7.2lf

16. End of File Controlled Loops
feof
int feof(FILE *fp)
Function to check if end of file has been reached.
For an end of file controlled loop
Read before the loop
Test for end of file: while (!feof(ptr))
Inside loop:
Process
Read at the bottom of the loop