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      vwprintf, vfwprintf, vswprintf, vwprintf_s, vfwprintf_s, vswprintf_s, vsnwprintf_s

      From cppreference.com
      <c‎ |io
       
       
      File input/output
      Types and objects
      Functions
      File access
      Unformatted input/output
      (C95)(C95)
      (C95)
      (C95)(C95)
      (C95)
      (C95)

      Formatted input
      Direct input/output
      Formatted output
      vwprintfvfwprintfvswprintfvwprintf_svfwprintf_svswprintf_svsnwprintf_s
      (C95)(C95)(C95)(C11)(C11)(C11)(C11)
      File positioning
      Error handling
      Operations on files
       
      Defined in header<wchar.h>
      (1)
      int vwprintf(constwchar_t* format, va_list vlist);
      		(since C95)
      (until C99)
      int vwprintf(constwchar_t*restrict format, va_list vlist);
      		(since C99)
      (2)
      int vfwprintf(FILE* stream,constwchar_t* format, va_list vlist);
      		(since C95)
      (until C99)
      int vfwprintf(FILE*restrict stream,
                     constwchar_t*restrict format, va_list vlist);
      		(since C99)
      (3)
      int vswprintf(wchar_t* buffer,size_t bufsz,
                     constwchar_t* format, va_list vlist);
      		(since C95)
      (until C99)
      int vswprintf(wchar_t*restrict buffer,size_t bufsz,
                     constwchar_t*restrict format, va_list vlist);
      		(since C99)
      int vwprintf_s(constwchar_t*restrict format, va_list vlist);
      		 (4)(since C11)
      int vfwprintf_s(FILE*restrict stream,
                       constwchar_t*restrict format, va_list vlist);
      		 (5)(since C11)
      int vswprintf_s(wchar_t*restrict buffer, rsize_t bufsz,
                       constwchar_t*restrict format, va_list vlist);
      		 (6)(since C11)
      int vsnwprintf_s(wchar_t*restrict buffer, rsize_t bufsz,
                       constwchar_t*restrict format, va_list vlist);
      		 (7)(since C11)

      Loads the data from locations, defined byvlist, converts them to wide string equivalents and writes the results to a variety of sinks.

      1) Writes the results tostdout.
      2) Writes the results to a file streamstream.
      3) Writes the results to a wide stringbuffer. At mostbufsz-1 wide characters are written followed by null wide character. The resulting wide character string will be terminated with a null wide character, unlessbufsz is zero.
      4-6) Same as(1-3), except that the following errors are detected at runtime and call the currently installedconstraint handler function:
      • the conversion specifier%n is present informat
      • any of the arguments corresponding to%s is a null pointer
      • format orbuffer is a null pointer
      • bufsz is zero or greater thanRSIZE_MAX/sizeof(wchar_t)
      • encoding errors occur in any of string and character conversion specifiers
      • (forvswprintf_s only), the string to be stored inbuffer (including the trailing wide null) would be exceedbufsz.
      7) Same as(6), except it will truncate the result to fit within the array pointed to bybuffer.
      As with all bounds-checked functions,vwprintf_s,vfwprintf_s,vswprintf_s, andvsnwprintf_s are only guaranteed to be available if__STDC_LIB_EXT1__ is defined by the implementation and if the user defines__STDC_WANT_LIB_EXT1__ to the integer constant1 before including<stdio.h>.

      Contents

      [edit]Parameters

      stream - output wide stream to write to
      buffer - pointer to a wide string to write to
      bufsz - maximum number of wide characters to write
      format - pointer to a null-terminated wide string specifying how to interpret the data
      vlist -variable argument list containing the data to print.


      Theformat string consists of ordinary wide characters (except%), which are copied unchanged into the output stream, and conversion specifications. Each conversion specification has the following format:

      • introductory% character.
      • (optional) one or more flags that modify the behavior of the conversion:
      • -: the result of the conversion is left-justified within the field (by default it is right-justified).
      • +: the sign of signed conversions is always prepended to the result of the conversion (by default the result is preceded by minus only when it is negative).
      • space: if the result of a signed conversion does not start with a sign character, or is empty, space is prepended to the result. It is ignored if+ flag is present.
      • #:alternative form of the conversion is performed. See the table below for exact effects otherwise the behavior is undefined.
      • 0: for integer and floating-point number conversions, leading zeros are used to pad the field instead ofspace characters. For integer numbers it is ignored if the precision is explicitly specified. For other conversions using this flag results in undefined behavior. It is ignored if- flag is present.
      • (optional) integer value or* that specifies minimum field width. The result is padded withspace characters (by default), if required, on the left when right-justified, or on the right if left-justified. In the case when* is used, the width is specified by an additional argument of typeint, which appears before the argument to be converted and the argument supplying precision if one is supplied. If the value of the argument is negative, it results with the- flag specified and positive field width (Note: This is the minimum width: The value is never truncated.).
      • (optional). followed by integer number or*, or neither that specifiesprecision of the conversion. In the case when* is used, theprecision is specified by an additional argument of typeint, which appears before the argument to be converted, but after the argument supplying minimum field width if one is supplied. If the value of this argument is negative, it is ignored. If neither a number nor* is used, the precision is taken as zero. See the table below for exact effects ofprecision.
      • (optional)length modifier that specifies the size of the argument (in combination with the conversion format specifier, it specifies the type of the corresponding argument).
      • conversion format specifier.

      The following format specifiers are available:

      Conversion
      Specifier      		ExplanationExpected
      Argument Type
      Length Modifier→hhhnonellljztL
      Only available since C99→YesYesYesYesYes
      %Writes literal%. The full conversion specification must be%%.N/AN/AN/AN/AN/AN/AN/AN/AN/A
      c

      Writes asingle character.

      • The argument is first converted towchar_t as if by callingbtowc.
      • If thel modifier is used, thewint_t argument is first converted towchar_t.
      		N/AN/A
      int
      wint_t
      		N/AN/AN/AN/AN/A
      s

      Writes acharacter string.

      • The argument must be a pointer to the initial element of a character array containing a multibyte character sequence beginning in the initial shift state, which is converted to wide character array as if by a call tombrtowc with zero-initialized conversion state.
      • Precision specifies the maximum number of wide characters to be written. IfPrecision is not specified, writes every wide characters up to and not including the first null terminator.
      • If thel specifier is used, the argument must be a pointer to the initial element of an array ofwchar_t.
      		N/AN/A
      char*
      wchar_t*
      		N/AN/AN/AN/AN/A
      d
      i

      Converts asigned integer into decimal representation[-]dddd.

      • Precision specifies the minimum number of digits to appear. The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      • For thez modifier, the expected argument type is the signed version ofsize_t.
      signedchar
      short
      int
      long
      longlong
      ※
      		N/A
      o

      Converts anunsigned integer into octal representationoooo.

      • Precision specifies the minimum number of digits to appear. The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      • In thealternative implementation precision is increased if necessary, to write one leading zero. In that case if both the converted value and the precision are​0​, single​0​ is written.
      unsignedchar
      unsignedshort
      unsignedint
      unsignedlong
      unsignedlonglong
      unsigned version ofptrdiff_t
      		N/A
      x
      X

      Converts anunsigned integer into hexadecimal representationhhhh.

      • For thex conversion lettersabcdef are used.
      • For theX conversion lettersABCDEF are used.
      • Precision specifies the minimum number of digits to appear. The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      • In thealternative implementation0x or0X is prefixed to results if the converted value is nonzero.
      		N/A
      u

      Converts anunsigned integer into decimal representationdddd.

      • Precision specifies the minimum number of digits to appear.
      • The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      		N/A
      f
      F (C99)

      Convertsfloating-point number to the decimal notation in the style[-]ddd.ddd.

      • Precision specifies the exact number of digits to appear after the decimal point character.
      • The default precision is6.
      • In thealternative implementation decimal point character is written even if no digits follow it.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/A
      double
      double(C99)
      		N/AN/AN/AN/A
      longdouble
      e
      E

      Convertsfloating-point number to the decimal exponent notation.

      • For thee conversion style[-]d.ddd e±dd is used.
      • For theE conversion style[-]d.ddd E±dd is used.
      • The exponent contains at least two digits, more digits are used only if necessary.
      • If the value is​0​, the exponent is also​0​.
      • Precision specifies the exact number of digits to appear after the decimal point character.
      • The default precision is6.
      • In thealternative implementation decimal point character is written even if no digits follow it.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/AN/AN/AN/AN/A
      a
      A

      (C99)

      Convertsfloating-point number to the hexadecimal exponent notation.

      • For thea conversion style[-] 0xh.hhh p±d is used.
      • For theA conversion style[-] 0Xh.hhh P±d is used.
      • The first hexadecimal digit is not0 if the argument is a normalized floating-point value.
      • If the value is​0​, the exponent is also​0​.
      • Precision specifies the exact number of digits to appear after the hexadecimal point character.
      • The default precision is sufficient for exact representation of the value.
      • In thealternative implementation decimal point character is written even if no digits follow it.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/AN/AN/AN/AN/A
      g
      G

      Convertsfloating-point number to decimal or decimal exponent notation depending on the value and theprecision.

      • For theg conversion style conversion with stylee orf will be performed.
      • For theG conversion style conversion with styleE orf(until C99)F(since C99) will be performed.
      • LetP equal the precision if nonzero,6 if the precision is not specified, or1 if the precision is​0​. Then, if a conversion with styleE would have an exponent ofX:
        • IfP > X ≥ −4, the conversion is with stylef orF(since C99) and precisionP − 1 − X.
        • Otherwise, the conversion is with stylee orE and precisionP − 1.
      • Unlessalternative representation is requested the trailing zeros are removed, also the decimal point character is removed if no fractional part is left.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/AN/AN/AN/AN/A
      n

      Returns thenumber of characters written so far by this call to the function.

      • The result iswritten to the value pointed to by the argument.
      • The specification may not contain anyflag,field width, orprecision.
      • For thez modifier, the expected argument type isS*, whereS is the signed version ofsize_t.
      signedchar*
      short*
      int*
      long*
      longlong*
      ※
      		N/A
      p

      Writes an implementation defined character sequence defining apointer.

      		N/AN/A
      void*
      		N/AN/AN/AN/AN/AN/A
      Notes

      The floating-point conversion functions convert infinity toinf orinfinity. Which one is used is implementation defined.

      Not-a-number is converted tonan ornan(char_sequence). Which one is used is implementation defined.

      The conversionsF,E,G,A outputINF,INFINITY,NAN instead.

      The conversion specifier used to printchar,unsignedchar,signedchar,short, andunsignedshort expects promoted types ofdefault argument promotions, but before printing its value will be converted tochar,unsignedchar,signedchar,short, andunsignedshort. It is safe to pass values of these types because of the promotion that takes place when a variadic function is called.

      The correct conversion specifications for the fixed-width character types (int8_t, etc) are defined in the header<inttypes.h> (althoughPRIdMAX,PRIuMAX, etc is synonymous with%jd,%ju, etc).

      The memory-writing conversion specifier%n is a common target of security exploits where format strings depend on user input and is not supported by the bounds-checkedprintf_s family of functions(since C11).

      There is asequence point after the action of each conversion specifier; this permits storing multiple%n results in the same variable or, as an edge case, printing a string modified by an earlier%n within the same call.

      If a conversion specification is invalid, the behavior is undefined.

      [edit]Return value

      1,4) The number of wide characters written if successful or negative value if an error occurred.
      3) The number of wide characters written if successful or negative value if an error occurred. If the resulting string gets truncated due tobufsz limit, function returns the total number of characters (not including the terminating null wide character) which would have been written, if the limit were not imposed.
      2,5) number of wide characters transmitted to the output stream or negative value if an output error, a runtime constraints violation error, or an encoding error occurred.
      6) number of wide characters written tobuffer, not counting the null wide character (which is always written as long asbuffer is not a null pointer andbufsz is not zero and not greater thanRSIZE_MAX/sizeof(wchar_t)), or zero on runtime constraint violations, and negative value on encoding errors.
      7) number of wide characters not including the terminating null character (which is always written as long asbuffer is not a null pointer andbufsz is not zero and not greater thanRSIZE_MAX/sizeof(wchar_t)), which would have been written tobuffer ifbufsz was ignored, or a negative value if a runtime constraints violation or an encoding error occurred.

      [edit]Notes

      All these functions invokeva_arg at least once, the value ofarg is indeterminate after the return. These functions to not invokeva_end, and it must be done by the caller.

      While narrow strings providevsnprintf, which makes it possible to determine the required output buffer size, there is no equivalent for wide strings (until C11's vsnwprintf_s), and in order to determine the buffer size, the program may need to callvswprintf, check the result value, and reallocate a larger buffer, trying again until successful.

      vsnwprintf_s, unlikevswprintf_s, will truncate the result to fit within the array pointed to bybuffer, even though truncation is treated as an error by most bounds-checked functions.

      [edit]Example

      Run this code
      #include <locale.h>#include <stdarg.h>#include <stddef.h>#include <stdio.h>#include <time.h>#include <wchar.h> void debug_wlog(constwchar_t* fmt, ...){struct timespec ts;    timespec_get(&ts, TIME_UTC);char time_buf[100];size_t rc=strftime(time_buf,sizeof time_buf,"%D %T",gmtime(&ts.tv_sec));snprintf(time_buf+ rc,sizeof time_buf- rc,".%06ld UTC", ts.tv_nsec/1000);     va_list args;    va_start(args, fmt);wchar_t buf[1024];int rc2= vswprintf(buf,sizeof buf/sizeof*buf, fmt, args);    va_end(args); if(rc2>0)wprintf(L"%s [debug]: %ls\n", time_buf, buf);elsewprintf(L"%s [debug]: (string too long)\n", time_buf);} int main(void){setlocale(LC_ALL,"");    debug_wlog(L"Logging, %d, %d, %d",1,2,3);}

      Possible output:

      02/20/15 22:12:38.476575 UTC [debug]: Logging, 1, 2, 3

      [edit]References

      • C23 standard (ISO/IEC 9899:2024):
      • 7.29.2.5 The vfwprintf function (p: TBD)
      • 7.29.2.7 The vswprintf function (p: TBD)
      • 7.29.2.9 The vwprintf function (p: TBD)
      • K.3.9.1.6 The vfwprintf_s function (p: TBD)
      • K.3.9.1.8 The vsnwprintf_s function (p: TBD)
      • K.3.9.1.9 The vswprintf_s function (p: TBD)
      • K.3.9.1.11 The vwprintf_s function (p: TBD)
      • C17 standard (ISO/IEC 9899:2018):
      • 7.29.2.5 The vfwprintf function (p: TBD)
      • 7.29.2.7 The vswprintf function (p: TBD)
      • 7.29.2.9 The vwprintf function (p: TBD)
      • K.3.9.1.6 The vfwprintf_s function (p: TBD)
      • K.3.9.1.8 The vsnwprintf_s function (p: TBD)
      • K.3.9.1.9 The vswprintf_s function (p: TBD)
      • K.3.9.1.11 The vwprintf_s function (p: TBD)
      • C11 standard (ISO/IEC 9899:2011):
      • 7.29.2.5 The vfwprintf function (p: 417-418)
      • 7.29.2.7 The vswprintf function (p: 419)
      • 7.29.2.9 The vwprintf function (p: 420)
      • K.3.9.1.6 The vfwprintf_s function (p: 632)
      • K.3.9.1.8 The vsnwprintf_s function (p: 633-634)
      • K.3.9.1.9 The vswprintf_s function (p: 634-635)
      • K.3.9.1.11 The vwprintf_s function (p: 636)
      • C99 standard (ISO/IEC 9899:1999):
      • 7.24.2.5 The vfwprintf function (p: 363)
      • 7.24.2.7 The vswprintf function (p: 364)
      • 7.24.2.9 The vwprintf function (p: 365)

      [edit]See also

      prints formatted output tostdout, a file stream or a buffer
      using variable argument list
      (function)[edit]
      prints formatted wide character output tostdout, a file stream or a buffer
      (function)[edit]
      C++ documentation forvwprintf,vfwprintf,vswprintf
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=c/io/vfwprintf&oldid=172069"
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