• The C input/output functions are declared in <stdio.h>
• We need to consider files, ASCII I/O and binary I/O

• File Variables:
  • C uses the FILE type for I/O
  • You declare a file variable as follows:

                  FILE  *input_file;
                 

• The Console:
  • If you only need to use "console I/O" (i.e., "standard in", "standard out", and "standard error"), which Java calls System.in, System.out, and System.err, you can use the FILE variables stdin, stdout, and stderr

• Background:
  • Files need to be opened before they can be used and closed when you are through with them
  • The standard files are opened and closed for you
• The fopen and fclose Functions:
  • FILE* fopen(const char* name, char* mode)
  • int fclose(FILE f)
• The Parameters:
  • name is (a pointer to) the name of the file
  • mode is used to control the properties of the file. A mode of "w" indicates that the file should be opened for writing (i.e., output) and a mode of "r" indicates that it should be opened for reading (i.e., input).

• Formats:
  • Many applications have to generate output in a particular format and/or read input files that are formatted in a particular way
  • C uses the variadic printf and scanf functions (and variants discussed below) for this purpose
• Syntax of the printf Function:
  • printf(format [, argument]...)
• Syntax of the scanf Function:
  • [number=]scanf(format [, argument]...)
• Parameters:
  • format denotes a format string
  • argument denotes the item to be input/output
  • number denotes the number of parameters successfully input

• Contents:
  • Literals
  • Conversion Specifications
• Conversion Specifications:
  • %[flags] [width] [.precision] [length] specifier
• Interpretation/Use:
  • flags - justification, leading characters, etc...
  • width - minimum number of characters to output
  • precision - number of decimal places or significant digits
  • length - specifies the size of the argument (e.g., l for long)

-	Left justify
0	Pad with 0s instead of blanks
+	Prepend the sign

d, i	Signed integer
f	Floating point
u	Unsigned integer
s	String (i.e., pointer to an array of char)
c	Character
o	Unsiged octal
x	Unsigned hexadecimal
e	Floating point in scientific notation
p	Pointer (as a character sequence)
n	Write the number of characters written so far to the given address

An Example

    int    n;

    printf("The answer is %d!", n);
  

• The fprintf Function:
  • fprintf(file, format [, argument]...);
• The fscanf Function:
  • [number=]fscanf(file, format [, argument]...)
• Parameters:
  • file denotes the FILE to use for input/output

• The sprintf function:
  • sprintf(string, format [, argument]...);
• Behavior:
  • Just like printf except that it does not write to an output device; it stores what would be printed in the given string
• The snprintf function:
  • Like sprintf except that the maximum number of characters is specified

• The fread Function:
  • [read_size = ] fread(data_pointer, 1,size, file);
• The fwrite Function:
  • [write_size = ] fwrite(data_pointer, 1,size, file);