printf的返回值

引自MSDN:

printf, wprintf

Print formatted output to the standard output stream.

int printf( const char *format [, argument]... );

int wprintf( const wchar_t *format [, argument]... );

Routine	Required Header	Compatibility
printf	<stdio.h>	ANSI, Win 95, Win NT
wprintf	<stdio.h> or <wchar.h>	ANSI, Win 95, Win NT

For additional compatibility information, see Compatibility in the Introduction.

Libraries

LIBC.LIB	Single thread static library, retail version
LIBCMT.LIB	Multithread static library, retail version
MSVCRT.LIB	Import library for MSVCRT.DLL, retail version

Return Value

Each of these functions returns the number of characters printed, or a negative value if an error occurs.

Parameters

format

Format control

argument

Optional arguments

Remarks

The printf 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. printf and fprintf behave identically except that printf writes output to stdout rather than to a destination of type FILE.

wprintf is a wide-character version of printf; format is a wide-character string. wprintf and printf behave identically otherwise.

Generic-Text Routine Mappings

TCHAR.H Routine	_UNICODE & _MBCS Not Defined	_MBCS Defined	_UNICODE Defined
_tprintf	printf	printf	wprintf

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("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 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.

Example

/* PRINTF.C: This program uses the printf and wprintf functions
 * to produce formatted output.
 */

#include <stdio.h>

void 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( "Integer formats:\n"
           "\tDecimal: %d  Justified: %.6d  Unsigned: %u\n",
           count, count, count, count );

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

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

   /* Display characters. */

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

   /* Display strings. */

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

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

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

   /* Count characters printed. */
   printf( "\nDisplay to here:\n" );
   printf( "1234567890123456%n78901234567890\n", &count );
   printf( "\tNumber displayed: %d\n\n", count );
}

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:   0012FFAC

Display to here:
123456789012345678901234567890
   Number displayed: 16