C Programming printf() Function

Last modified by Microchip on 2023/11/09 09:06


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

Key Points

  • Prints ControlString to Standard Output (the terminal on a PC, typically a Universal Asynchronous Receiver Transmitter (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 (arg1, …, argN above) can be variables or other data to be embedded within ControlString
  • Placeholders are put in ControlString to indicate where the value of an argument parameter should be inserted
  • Placeholders indicate the position in string and format to be used in printing data embedded within ControlString
  • printf() requires a huge amount of memory. Best used for debugging only unless you need all of its functionality
1    {
2          int a = 5;
3          int b = 10;
4          printf("a = %d\nb = %d\n", a, b);
5    }


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

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Format Specifiers

Format SpecifierMeaning
%cSingle character
%sString (all characters until '\0')
%dSigned decimal integer
%oUnsigned octal integer
%uUnsigned decimal integer
%xUnsigned hexadecimal integer with lower case digits (e.g. 1a5e)
%XSame as %x but with upper case digits (e.g. 1A5E)
%fSigned decimal value (floating point)
%eSigned decimal value with exponent (e.g. 1.26e-5)
%ESame as %e but uses upper case E for exponent (e.g. 1.26E-5)
%gSame as %e or %f, depending on size and precision of value
%GSame as %g but will use capital E for exponent

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