vfprintf() -- STDIO Function (libc)

Print formatted text into stream
#include <stdarg.h>
#include <stdio.h>
int
vfprintf(fp, format, arguments)
FILE*fp; char *format; va_list arguments;

vfprintf()  constructs a  formatted string  and writes  it into  the stream
pointed  to by  fp.  It translates  integers,  floating-point numbers,  and
strings into  a variety of text formats.  vfprintf()  can handle a variable
list  of  arguments  of   various  types.   It  is  roughly  equivalent  to
fprintf()'s conversion specifier %r.

format points  to a string that can contain  text, character constants, and
one  or   more  conversion  specifications.    A  conversion  specification
describes how to convert a particular data type into text.  Each conversion
specification is introduced with the percent sign `%'.  (To print a literal
percent  sign, use  the  escape sequence  `%%'.) See  printf() for  further
discussion of  the conversion  specification, and for  a table of  the type
specifiers that can be used with vfprintf().

After format comes arguments. This is  of type va_list, which is defined in
the header  file stdarg.h. It has been initialized  by the macro va_start()
and points  to the base  of the list  of arguments used  by vfprintf(). For
more information, see the Lexicon entry for va_arg().

arguments should  access one argument for  each conversion specification in
format,  of the  type  appropriate to  its  conversion specification.   For
example, if  format contains conversion specifications for  an int, a long,
and a  string, then arguments access  three arguments, being, respectively,
an  int, a  long, and  a char  *. arguments  can take  only the  data types
acceptable  to the  macro va_arg(),  namely,  the basic  types that  can be
converted to  pointers simply  by adding  a `*' after  the type  name.  See
va_arg() for more information on this point.

If  there   are  fewer  arguments  than   conversion  specifications,  then
vfprintf()'s behavior is  undefined (and probably unwelcome).  If there are
more,  vfprintf()  evaluates  and then  ignores  every  argument without  a
corresponding conversion specification.  If  an argument is not of the same
type  as  its  corresponding conversion  specifier,  then  the behavior  of
vfprintf() is undefined.   Thus, presenting an int where vfprintf() expects
a char * may generate unwelcome results.

If it  wrote the formatted string correctly,  vfprintf() returns the number
of characters written.  Otherwise, it returns a negative number.

See Also

fprintf(),
libc,
printf(),
sprintf(),
vprintf(),
vsprintf()
ANSI Standard, §7.9.6.7

Notes

vfprintf() can construct a string up to at least 509 characters long.

© 2012 by Stephen A. Ness