CSE 2031 Lecture 9

Assignment FAQ

Output files as they are read. For first question : instead of outputting palendromes output 'line is too long' after a certain length.

file* ß fopen(…)

file* fp;

fp = fopen("temp","a");

fprintf(fp,'%s\n", "Hello");

.

.

.

fclose(fp);

printf == fprintf(stdout,…);

"r+" opens a file for reading and writing

"w+" creates a file or truncates it if it exists and reads and writes to it

File descriptor talks to offset talks to inode

When you give a command like write you specify a file descriptor, where you find the data and how much you want to write

A file is a sequence of bytes,

Fseek, frewind, fsetpos are ways to specify the file pointer and where in the file you would like to go in the offset

States of a stream

• Opened
  
  • If you write you go to ..
    
    • Writing state
      
      • If you continue writing you stay in the write state
        
      • If you use seek or rewind you will go back to
        
        • Opened state
          
      • If you just finished writing then you read
        
        • Error state
          
  • If you read you go to
    
    • Reading state
      
      • If you continue reading you stay in the read state
        
      • I f you just finished reading then you write
        
        • Error state
          

 

Printf(format string; other args)

Format string

• Literal text
  
• Conversion specifier
  
  • Printf("hello world \n");
    
  • ^literal text
    
• Printf("n=%d\n", n);
  
  • Literal text
    
    • "n=" + "\n"
      
  • Conversion specifier
    
    • "%d"
      
  • Other arguments
    
    • "n"
      
• Using print f
  
  • A char and short is always converted to int
    
  • A float is always converted to double
    

Conversion specifier

• Starts with "%"
  
  • 4 components (in order)
    
    • Flags
      
    • Field width
      
    • Precision
      
    • Conversion specifier
      
      • first 3 are optional
        

 

d,i	Int	[-]ddd (where d are digits)
u	Unsigned int	ddd
o	Unsigned int	ddd 0-7
x	Unsigned int	ddd 0-9 a-f
X	Unsigned int	ddd 0-9 A-F

 

f	Double	[-]ddd.ddd
E,e	Double	[-]d.ddd e/E +/- dd
G,g	Double	-4<= exponent <precision (life f or e,E
c	Int	Treats int as unsigned char Prints the character
S	Char*	Output chars from array up to '\0'
P	Void*	System dependant Prints an address, usually in hexidecimal
N	Int*	Stores in variable; # of characters printed so far. No conversion
%		Writes a '%' sign

 

Length specifier in conversion specifier

• h,l,L
  
• you can have the h in front on the integer conversion specifiers
  
  • conversion specifier applies to short int (unsigned short int)
    
  • remember char / short args already promoted to int
    
  • convert arg to short before printing
    
• the L,f,e,E,g,G conversion specifier applies to long double argument
  
• do now use lowercase l or h with f,e,E,g,G
  

flags

• field width
  
  • %5d
    
    • Decimal no sign
      
    • Field width of size 5
      
  • %-d
    
    • Fiend width 5
      
    • '-' is a flag
      
      • Left jusitication
        
  • %*d
    
    • Take next arg as field width
      
    • Scanf("%*lf, …)
      
      • * in scanf the * says read a double from input
        

Precision

• After the period
  
• %.5d
  
  • Min # digits to output, pad left w/ 0's
    
• %.5f
  
  • # of fraction digits
    
• %.5g
  
  • Max # of significant digits
    
• &.5s
  
  • Max # of characters to print from the string
    

Flags

• -
  
  • Left justify
    
• 0
  
  • Pads with 0's
    
• +
  
  • Forces explicit plus sign
    
• ' ' (space)
  
  • Use a space instead of plus sign in the output
    
• #
  
  • Changes conversions
    
  • 0 à leading 0
    
  • %#F
    
    • The decimal sign is printed even if there is nothing after it