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printf_s, _printf_s_l, wprintf_s, _wprintf_s_l

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Prints formatted output to the standard output stream. These versions of printf, _printf_l, wprintf, _wprintf_l have security enhancements, as described in Security features in the CRT.

Syntax

int printf_s(
   const char *format [,
   argument]...
);
int _printf_s_l(
   const char *format,
   _locale_t locale [,
   argument]...
);
int wprintf_s(
   const wchar_t *format [,
   argument]...
);
int _wprintf_s_l(
   const wchar_t *format,
   _locale_t locale [,
   argument]...
);

Parameters

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.

Remarks

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 errno, _doserrno, _sys_errlist, and _sys_nerr.

printf_s and fprintf_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 and _MBCS not defined _MBCS defined _UNICODE defined
_tprintf_s printf_s printf_s wprintf_s
_tprintf_s_l _printf_s_l _printf_s_l _wprintf_s_l

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 aren't enough arguments for all the format specifications.

Important

Ensure that format is not a user-defined string.

Starting in Windows 10 version 2004 (build 19041), the printf family of functions prints exactly representable floating point numbers according to the IEEE 754 rules for rounding. In previous versions of Windows, exactly representable floating point numbers ending in '5' would always round up. IEEE 754 states that they must round to the closest even digit (also known as "Banker's Rounding"). For example, both printf("%1.0f", 1.5) and printf("%1.0f", 2.5) should round to 2. Previously, 1.5 would round to 2 and 2.5 would round to 3. This change only affects exactly representable numbers. For example, 2.35 (which, when represented in memory, is closer to 2.35000000000000008) continues to round up to 2.4. Rounding done by these functions now also respects the floating point rounding mode set by fesetround. Previously, rounding always chose FE_TONEAREST behavior. This change only affects programs built using Visual Studio 2019 version 16.2 and later. To use the legacy floating point rounding behavior, link with legacy_stdio_float_rounding.obj.

Requirements

Routine Required header
printf_s, _printf_s_l <stdio.h>
wprintf_s, _wprintf_s_l <stdio.h> or <wchar.h>

The console isn't supported in Universal Windows Platform (UWP) apps. The standard stream handles that are associated with the console, stdin, stdout, and stderr, must be redirected before C run-time functions can use them in UWP apps. For more compatibility information, see Compatibility.

The console isn't supported in Universal Windows Platform (UWP) apps. The standard stream handles that are associated with the console, stdin, stdout, and stderr, must be redirected before C run-time functions can use them in UWP apps. For more compatibility information, see Compatibility.

Example

// 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):
                 computer
                     comp
   Unicode                      Uni
Strings in field (2):
                 computer
                     comp
   Unicode                      Uni
Real numbers:
   251.736600 251.74 2.517366e+002 2.517366E+002

Address as:   0012FF78

See also

Math and floating-point support
Stream I/O
Locale
fopen, _wfopen
fprintf, _fprintf_l, fwprintf, _fwprintf_l
scanf, _scanf_l, wscanf, _wscanf_l
sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l
vprintf functions