std::vprintf,std::vfprintf,std::vsprintf,std::vsnprintf(3)

NAME
std::vprintf,std::vfprintf,std::vsprintf,std::vsnprintf - std::vprintf,std::vfprintf,std::vsprintf,std::vsnprintf

Synopsis
   Defined in header <cstdio>
   int vprintf( const char* format, va_list vlist ); (1)
   int vfprintf( std::FILE* stream, const char* format, va_list vlist (2)
   );
   int vsprintf( char* buffer, const char* format, va_list vlist ); (3)
   int vsnprintf( char* buffer, std::size_t buf_size, const char* (4) (since C++11)
   format, va_list vlist );
   Loads the data from the locations, defined by vlist, converts them to character
   string equivalents and writes the results to a variety of sinks.
   1) Writes the results to stdout.
   2) Writes the results to a file stream stream.
   3) Writes the results to a character string buffer.
   4) Writes the results to a character string buffer. At most buf_size-1 characters
   are written. The resulting character string will be terminated with a null
   character, unless buf_size is zero. If buf_size is zero, nothing is written and
   buffer may be a null pointer, however the return value (number of bytes that would
   be written not including the null terminator) is still calculated and returned.

Parameters
   stream - output file stream to write to
   buffer - pointer to a character string to write to
   buf_size - maximum number of characters to write
   format - pointer to a null-terminated character string specifying how to interpret
              the data
   vlist - variable argument list containing the data to print.
   The format string consists of ordinary multibyte 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 of space
                        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 with space 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 type int, 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 specifies
                precision of the conversion. In the case when * is used, the precision
                is specified by an additional argument of type int, 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 of
                precision.
              * (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 Explanation Expected Specifier Argument Type
           Length hh ll j z t
        Modifier→ h (none) l L
                        (C++11) (C++11) (C++11) (C++11) (C++11)
           writes literal %.
           The full
    % conversion N/A N/A N/A N/A N/A N/A N/A N/A N/A
           specification
           must be %%.
              writes a
              single
              character.
           The argument is
           first converted
           to unsigned char.
    c If the l modifier N/A N/A int wint_t N/A N/A N/A N/A N/A
           is used, the
           argument is first
           converted to a
           character string
           as if by %ls with
           a wchar_t[2]
           argument.
              writes a
              character
              string
           The argument must
           be a pointer to
           the initial
           element of an
           array of
           characters.
           Precision
           specifies the
           maximum number of
           bytes to be
           written. If
           Precision is not
    s specified, writes N/A N/A char* wchar_t* N/A N/A N/A N/A N/A
           every byte up to
           and not including
           the first null
           terminator. If
           the l specifier
           is used, the
           argument must be
           a pointer to the
           initial element
           of an array of
           wchar_t, which is
           converted to char
           array as if by a
           call to wcrtomb
           with
           zero-initialized
           conversion state.
              converts a
              signed integer
              into decimal
              representation
              [-]dddd.
           Precision
           specifies the
    d minimum number of signed long signed
    i digits to appear. char short int long long intmax_t size_t ptrdiff_t N/A
           The default
           precision is 1.
           If both the
           converted value
           and the precision
           are 0 the
           conversion
           results in no
           characters.
              converts an
              unsigned
              integer into
              octal
              representation
              oooo.
           Precision
           specifies the
           minimum number of
           digits to appear.
           The default
           precision is 1.
           If both the
           converted value
           and the precision
    o are 0 the N/A
           conversion
           results in no
           characters. In
           the alternative
           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.
              converts an
              unsigned
              integer into
              hexadecimal
              representation
              hhhh.
           For the x
           conversion
           letters abcdef unsigned unsigned unsigned unsigned unsigned unsigned
           are used. char short int long long uintmax_t size_t version of
           For the X long ptrdiff_t
           conversion
           letters ABCDEF
           are used.
           Precision
    x specifies the N/A
    X minimum number of
           digits to appear.
           The default
           precision is 1.
           If both the
           converted value
           and the precision
           are 0 the
           conversion
           results in no
           characters. In
           the alternative
           implementation 0x
           or 0X is prefixed
           to results if the
           converted value
           is nonzero.
              converts an
              unsigned
              integer into
              decimal
              representation
              dddd.
           Precision
           specifies the
    u minimum number of N/A
           digits to appear.
           The default
           precision is 1.
           If both the
           converted value
           and the precision
           are 0 the
           conversion
           results in no
           characters.
              converts
              floating-point
              number to the
              decimal
              notation in
              the style
              [-]ddd.ddd.
           Precision
           specifies the
           exact number of
           digits to appear
    f after the decimal
    F point character. N/A N/A N/A N/A N/A N/A
           The default
           precision is 6.
           In the
           alternative
           implementation
           decimal point
           character is
           written even if
           no digits follow
           it. For infinity
           and not-a-number
           conversion style
           see notes.
              converts
              floating-point
              number to the
              decimal
              exponent
              notation.
           For the e
           conversion style
           [-]d.ddde±dd is
           used.
           For the E
           conversion style
           [-]d.dddE±dd is
           used.
           The exponent
           contains at least
           two digits, more
           digits are used
           only if
    e necessary. If the
    E value is 0, N/A N/A N/A N/A N/A N/A
           the exponent is
           also 0.
           Precision
           specifies the
           exact number of
           digits to appear
           after the decimal
           point character.
           The default
           precision is 6.
           In the
           alternative
           implementation
           decimal point
           character is
           written even if
           no digits follow
           it. For infinity
           and not-a-number
           conversion style
           see notes.
              converts
              floating-point
              number to the
              hexadecimal
              exponent
              notation.
           For the a
           conversion style
           [-]0xh.hhhp±d is
           used.
           For the A
           conversion style
           [-]0Xh.hhhP±d is
           used.
           The first
           hexadecimal digit
           is not 0 if the
           argument is a
           normalized double double long
           floating point (C++11) double
    a value. If the
    A value is 0,
           the exponent is N/A N/A N/A N/A N/A N/A
 (C++11) 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 the
           alternative
           implementation
           decimal point
           character is
           written even if
           no digits follow
           it. For infinity
           and not-a-number
           conversion style
           see notes.
              converts
              floating-point
              number to
              decimal or
              decimal
              exponent
              notation
              depending on
              the value and
              the precision.
           For the g
           conversion style
           conversion with
           style e or f will
           be performed.
           For the G
           conversion style
           conversion with
           style E or F will
           be performed.
           Let P equal the
           precision if
           nonzero, 6 if the
           precision is not
           specified, or 1
           if the precision
           is 0. Then,
           if a conversion
           with style E
    g would have an
    G exponent of X: N/A N/A N/A N/A N/A N/A
             * if P > X ≥
               −4, the
               conversion is
               with style f
               or F and
               precision P
               − 1 − X.
             * otherwise,
               the
               conversion is
               with style e
               or E and
               precision P
               − 1.
           Unless
           alternative
           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
           see notes.
              returns the
              number of
              characters
              written so far
              by this call
              to the
              function.
                        signed long signed
    n The result is char* short* int* long* long* intmax_t* size_t* ptrdiff_t* N/A
           written to the
           value pointed to
           by the argument.
           The specification
           may not contain
           any flag, field
           width, or
           precision.
           writes an
           implementation
    p defined character N/A N/A void* N/A N/A N/A N/A N/A N/A
           sequence defining
           a pointer.
   The floating point conversion functions convert infinity to inf or infinity. Which
   one is used is implementation defined.
   Not-a-number is converted to nan or nan(char_sequence). Which one is used is
   implementation defined.
   The conversions F, E, G, A output INF, INFINITY, NAN instead.
   Even though %c expects int argument, it is safe to pass a char because of the
   integer 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 <cinttypes> (although PRIdMAX, 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-checked
   printf_s family of functions.
   There is a sequence 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.

Return value
   1-3) Number of characters written if successful or negative value if an error
   occurred.
   4) Number of characters written if successful or negative value if an error
   occurred. If the resulting string gets truncated due to buf_size limit, function
   returns the total number of characters (not including the terminating null-byte)
   which would have been written, if the limit was not imposed.

Notes
   All these functions invoke va_arg at least once, the value of arg is indeterminate
   after the return. These functions do not invoke va_end, and it must be done by the
   caller.

Example
// Run this code
 #include <vector>
 #include <cstdio>
 #include <cstdarg>
 #include <ctime>
 void debug_log(const char *fmt, ...)
 {
     std::time_t t = std::time(nullptr);
     char time_buf[100];
     std::strftime(time_buf, sizeof time_buf, "%D %T", std::gmtime(&t));
     va_list args1;
     va_start(args1, fmt);
     va_list args2;
     va_copy(args2, args1);
     std::vector<char> buf(1+std::vsnprintf(nullptr, 0, fmt, args1));
     va_end(args1);
     std::vsnprintf(buf.data(), buf.size(), fmt, args2);
     va_end(args2);
     std::printf("%s [debug]: %s\n", time_buf, buf.data());
 }
 int main()
 {
     debug_log("Logging, %d, %d, %d", 1, 2, 3);
 }

Output:
 04/13/15 15:09:18 [debug]: Logging, 1, 2, 3

See also
   printf
   fprintf prints formatted output to stdout, a file stream or a buffer
   sprintf (function)
   snprintf
   (C++11)
   vscanf
   vfscanf reads formatted input from stdin, a file stream or a buffer
   vsscanf using variable argument list
   (C++11) (function)
   (C++11)
   (C++11)