printf_s, _printf_s_l, wprintf_s, _wprintf_s_l

Print formatted output to the standard output stream. These are versions of printf, _printf_l, wprintf, _wprintf_l with security enhancements as described in Security Enhancements in the CRT.

int printf_s(
   const char *format [,
int _printf_s_l(
   const char *format,
   locale_t locale [,
int wprintf_s(
   const wchar_t *format [,
int _wprintf_s_l(
   const wchar_t *format,
   locale_t locale [,


  • format
    Format control.

  • argument
    Optional arguments.

  • locale
    The locale to use.

Return Value

Returns the number of characters printed, or a negative value if an error occurs.


The printf_s function formats and prints a series of characters and values to the standard output stream, stdout. If arguments follow the format string, the format string must contain specifications that determine the output format for the arguments.

The main difference between printf_s and printf is that printf_s checks the format string for valid formatting characters, whereas printf only checks if the format string is a null pointer. If either check fails, an invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, the function returns -1 and sets errno to EINVAL.

For information on errno and error codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.

printf_sandfprintf_s behave identically except that printf_s writes output to stdout rather than to a destination of type FILE. For more information, see fprintf_s, _fprintf_s_l, fwprintf_s, _fwprintf_s_l.

wprintf_s is a wide-character version of printf_s; format is a wide-character string. wprintf_s and printf_s behave identically if the stream is opened in ANSI mode. printf_s doesn't currently support output into a UNICODE stream.

The versions of these functions with the _l suffix are identical except that they use the locale parameter passed in instead of the current thread locale.

Generic-Text Routine Mappings

TCHAR.H routine

_UNICODE & _MBCS not defined

_MBCS defined

_unicode defined









The format argument consists of ordinary characters, escape sequences, and (if arguments follow format) format specifications. The ordinary characters and escape sequences are copied to stdout in order of their appearance. For example, the line

printf_s("Line one\n\t\tLine two\n"); 

produces the output

Line one
        Line two

Format specifications always begin with a percent sign (%) and are read left to right. When printf_s encounters the first format specification (if any), it converts the value of the first argument after format and outputs it accordingly. The second format specification causes the second argument to be converted and output, and so on. If there are more arguments than there are format specifications, the extra arguments are ignored. The results are undefined if there are not enough arguments for all the format specifications.

Security noteSecurity Note:

Ensure that format is not a user-defined string.



Required header

printf_s, _printf_s_l


wprintf_s, _wprintf_s_l

<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.


// crt_printf_s.c
/* This program uses the printf_s and wprintf_s functions
 * to produce formatted output.

#include <stdio.h>

int main( void )
   char   ch = 'h', *string = "computer";
   int    count = -9234;
   double fp = 251.7366;
   wchar_t wch = L'w', *wstring = L"Unicode";

   /* Display integers. */
   printf_s( "Integer formats:\n"
           "   Decimal: %d  Justified: %.6d  Unsigned: %u\n",
           count, count, count );

   printf_s( "Decimal %d as:\n   Hex: %Xh  C hex: 0x%x  Octal: %o\n",
            count, count, count, count );

   /* Display in different radixes. */
   printf_s( "Digits 10 equal:\n   Hex: %i  Octal: %i  Decimal: %i\n",
            0x10, 010, 10 );

   /* Display characters. */

   printf_s("Characters in field (1):\n%10c%5hc%5C%5lc\n", ch, ch, wch, wch);
   wprintf_s(L"Characters in field (2):\n%10C%5hc%5c%5lc\n", ch, ch, wch, wch);

   /* Display strings. */

   printf_s("Strings in field (1):\n%25s\n%25.4hs\n   %S%25.3ls\n",
   string, string, wstring, wstring);
   wprintf_s(L"Strings in field (2):\n%25S\n%25.4hs\n   %s%25.3ls\n",
       string, string, wstring, wstring);

   /* Display real numbers. */
   printf_s( "Real numbers:\n   %f %.2f %e %E\n", fp, fp, fp, fp );

   /* Display pointer. */
   printf_s( "\nAddress as:   %p\n", &count);


Sample Output

Integer formats:
   Decimal: -9234  Justified: -009234  Unsigned: 4294958062
Decimal -9234 as:
   Hex: FFFFDBEEh  C hex: 0xffffdbee  Octal: 37777755756
Digits 10 equal:
   Hex: 16  Octal: 8  Decimal: 10
Characters in field (1):
         h    h    w    w
Characters in field (2):
         h    h    w    w
Strings in field (1):
   Unicode                      Uni
Strings in field (2):
   Unicode                      Uni
Real numbers:
   251.736600 251.74 2.517366e+002 2.517366E+002

Address as:   0012FF78

.NET Framework Equivalent

See Also


Floating-Point Support

Stream I/O


fopen, _wfopen

fprintf, _fprintf_l, fwprintf, _fwprintf_l

scanf, _scanf_l, wscanf, _wscanf_l

sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l

vprintf Functions