Format specification in I/O

#include 
int printf( const char *format, ... );

Description:
The printf() function prints output to STDOUT, according to format and other arguments passed to printf(). The string format consists of two types of items - characters that will be printed to the screen, and format commands that define how the other arguments to printf() are displayed. Basically, you specify a format string that has text in it, as well as "special" characters that map to the other arguments of printf().

The %s means, "insert the first argument, a string, right here." The %d indicates that the second argument (an integer) should be placed there. There are different %-codes for different variable types, as well as options to limit the length of the variables and whatnot.

Code  Format                

----    ------

%c  character

%d  signed integers

%i  signed integers

%e  scientific notation, with a lowercase "e"

%E  scientific notation, with a uppercase "E"

%f  floating point

%g  use %e or %f, whichever is shorter

%G  use %E or %f, whichever is shorter

%o  octal

%s  a string of characters

%u  unsigned integer

%x  unsigned hexadecimal, with lowercase letters

%X  unsigned hexadecimal, with uppercase letters

%p  a pointer

%n  the argument shall be a pointer to an integer into which is placed the number of characters written so far

%%  a '%' sign

Precision = 1 for int types(d,i,x,X,o,u), 6 for float(f,eE but not g,G), infinite for s.
An integer placed between a % sign and the format command acts as a minimum field width specifier, and pads the output with spaces or zeros to make it long enough. If you want to pad with zeros, place a zero before the minimum field width specifier. You can use a precision modifier, which has different meanings depending on the format code being used.

• With %e, %E, and %f, the precision modifier lets you specify the number of decimal places desired. For example,
  
  
  

  %12.6f

  
  
  will display a floating number at least 12 digits wide, with six decimal places.
  
• With %g and %G, the precision modifier determines the maximum number of significant digits displayed.
• With %s, the precision modifer simply acts as a maximum field length, to complement the minimum field length that precedes the period.

All of printf()'s output is right-justified, unless you place a minus sign right after the % sign. For example,

%-12.4f  //left justification

will display a floating point number with a minimum of 12 characters, 4 decimal places, and left justified. You may modify the %d, %i, %o, %u, and %x type specifiers with the letter l and the letter h to specify long and short data types (e.g. %hd means a short integer). The %e, %f, and %g type specifiers can have the letter l before them to indicate that a double follows.
#
The %g, %f, and %e type specifiers can be preceded with the character '#' to ensure that the decimal point will be present, even if there are no decimal digits. The use of the '#' character with the %x type specifier indicates that the hexidecimal number should be printed with the '0x' prefix. The use of the '#' character with the %o type specifier indicates that the octal value should be displayed with a 0 prefix.

You can also include constant escape sequences in the output string.

The return value of printf() is the number of characters printed, or a negative number if an error occurred.

Example:

char name[20] = "Bob";
int age = 21;
printf( "Hello %s, you are %d years old\n", name, age );

OUTPUT: Hello Bob, you are 21 years old

Other Functions using formats

#include 

int fprintf(FILE *stream, const char *format, ...);
int printf(const char *format, ...);
int sprintf(char *s, const char *format, ...);

#include      /* as well as stdio.h */
int vfprintf(FILE *stream, const char *format, va list arg);
int vprintf(const char *format, va list arg);
int vsprintf(char *s, const char *format, va list arg);

      
Name
      
Purpose
     

      
fprintf
      
General formatted output  as  described.       Output  is written to the file indicated       by stream.
     
      
printf
      
Identical  to  fprintf  with   a   first       argument equal to stdout.
     
      
sprintf
      
Identical to  fprintf  except  that  the       output  is  not  written  to a file, but       written into the character array pointed       to by s.
     
      
vfprintf
      
Formatted output  as  for  fprintf,  but       with the variable argument list replaced       by arg which must have been  initialized       by  va_start. va_end  is not called by       this function.
     
      
vprintf
      
Identical  to  vfprintf  with  a   first       argument equal to stdout.
     
      
vsprintf
      
Formatted output  as  for  sprintf,  but       with the variable argument list replaced       by arg which must have been  initialized       by  va_start.   va_end  is not called by       this function.