The printf() Function

Syntax

printf("ControlString", arg1,, argN);

Key Points

  • Prints ControlString to Standard Output (the terminal on a PC, typicaly a UART on microcontrollers)
  • The MPLAB® X IDE Simulator uses the UART1 Output window to display text written to the UART using printf().
  • All comma separated parameters are optional except for ControlString
  • The argument parameters (arg1argN above) can be variables or other data to be embedded within ControlString
  • Placeholders are put in ControlString to indicate where value of an argument parameter should be inserted
  • Placeholders indicate position in string and format to be used in printing data embedded within ControlString
  • printf() requires huge amount of memory. Best used for debugging only unless you need all of its functionality.

Example 1

printf2.png

The code above would produce the following output:

a = 5
b = 10
_

Where "_" indicates the position of the cursor at the end of the operation.

  • The code in Example 1 defines two variables: a and b.
  • We want to print their values as part of a string that indicates which value goes with which variable.
  • The ControlString is "a = %d\nb = %d\n".
  • Each %d is a placeholder that indicates where one of the arguments should be inserted and how it should be formatted when printed.
  • The value of a is inserted at the position of the first %d and the value of b is inserted at the position of the second %d.
  • The d in the %d is called a format specifier or a conversion character and indicates that the value should be printed as a signed decimal integer.
  • The \n is an escape sequence indicating that a new line should be inserted, causing the cursor to go down to the next line before continuing to print.

Format Specifiers

Format Specifier Meaning
%c Single character
%s String (all characters until '\0')
%d Signed decimal integer
%o Unsigned octal integer
%u Unsigned decimal integer
%x Unsigned hexadecimal integer with lower case digits (e.g. 1a5e)
%X Same as %x but with upper case digits (e.g. 1A5E)
%f Signed decimal value (floating point)
%e Signed decimal value with exponent (e.g. 1.26e-5)
%E Same as %e but uses upper case E for exponent (e.g. 1.26E-5)
%g Same as %e or %f, depending on size and precision of value
%G Same as %g but will use capital E for exponent

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