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scanf(3c)

Standard C Library Functions                                         scanf(3C)



NAME
       scanf,  fscanf,  sscanf,  vscanf,  vfscanf, vsscanf - convert formatted
       input
       scanf_s, fscanf_s, sscanf_s, vscanf_s, vfscanf_s, vsscanf_s  -  convert
       formatted input with additional safety checks

SYNOPSIS
       #include <stdio.h>

       int scanf(const char *restrict format, ...);


       int fscanf(FILE *restrict stream, const char *restrict format, ...);


       int sscanf(const char *restrict s, const char *restrict format, ...);


       #include <stdarg.h>
       #include <stdio.h>


       int vscanf(const char *format, va_list arg);


       int vfscanf(FILE *stream, const char *format, va_list arg);


       int vsscanf(const char *s, const char *format, va_list arg);


       #define __STDC_WANT_LIB_EXT1__ 1
       #include <stdio.h>

       int scanf_s(const char *restrict format, ...);


       int fscanf_s(FILE *restrict stream, const char *restrict format, ...);


       int sscanf_s(const char *restrict s,
           const char *restrict format, ...);


       #define __STDC_WANT_LIB_EXT1__1
       #include <stdarg.h>
       #include <stdio.h>


       int vscanf_s(const char *restrict format, va_list arg);


       int vfscanf_s(FILE *restrict stream, const char *restrict format,
           va_list arg);


       int vsscanf_s(const char *restrict s, const char *restrict format,
           va_list arg);

DESCRIPTION
       The scanf() function reads from the standard input stream stdin.


       The fscanf() function reads from the named input stream.


       The sscanf() function reads from the string s.


       The  vscanf(),  vfscanf(),  and  vsscanf() functions are similar to the
       scanf(), fscanf(), and sscanf() functions,  respectively,  except  that
       instead  of  being called with a variable number of arguments, they are
       called with an argument list as defined by the <stdarg.h> header. These
       functions  do  not  invoke the va_end() macro. Applications using these
       functions should call va_end(ap) afterwards to clean up.


       Each function reads bytes, interprets them according to a  format,  and
       stores the results in its arguments. Each expects, as arguments, a con‐
       trol string format described below, and  a  set  of  pointer  arguments
       indicating  where  the  converted input should be stored. The result is
       undefined if there are insufficient arguments for the  format.  If  the
       format  is  exhausted  while arguments remain, the excess arguments are
       evaluated but are otherwise ignored.


       Conversions can be applied to the nth argument after the format in  the
       argument  list,  rather than to the next unused argument. In this case,
       the conversion character % (see below) is replaced by the sequence %n$,
       where  n is a decimal integer in the range [1, NL_ARGMAX]. This feature
       provides for the definition of format strings that select arguments  in
       an  order appropriate to specific languages. In format strings contain‐
       ing the %n$  form  of  conversion  specifications,  it  is  unspecified
       whether  numbered arguments in the argument list can be referenced from
       the format string more than once.


       The format can contain either form of a conversion specification,  that
       is,  % or %n$, but the two forms cannot normally be mixed within a sin‐
       gle format string. The only exception to this is that %% or %*  can  be
       mixed with the %n$ form.


       The  scanf()  function  in all its forms allows for detection of a lan‐
       guage-dependent radix character in the input string. The radix  charac‐
       ter  is  defined  in the program's locale (category LC_NUMERIC). In the
       POSIX locale, or in a locale where the radix character is not  defined,
       the radix character defaults to a period (.).


       The  format  is a character string, beginning and ending in its initial
       shift state, if any, composed of zero or more directives.  Each  direc‐
       tive is composed of one of the following:

           o      one  or  more  white-space  characters (space, tab, newline,
                  vertical-tab or form-feed characters);


           o      an ordinary character (neither % nor a  white-space  charac‐
                  ter); or


           o      a conversion specification.


   Conversion Specifications
       Each  conversion  specification is introduced by the character % or the
       character sequence %n$, after which the following appear in sequence:

           o      An optional assignment-suppressing character *.


           o      An optional non-zero decimal integer that specifies the max‐
                  imum field width.


           o      An  option  length  modifier  that specifies the size of the
                  receiving object.


           o      A conversion specifier character that specifies the type  of
                  conversion  to  be  applied. The valid conversion characters
                  are described below.



       The scanf() functions execute each directive of the format in turn.  If
       a  directive  fails,  as detailed below, the function returns. Failures
       are described as input failures (due to  the  unavailability  of  input
       bytes) or matching failures (due to inappropriate input).


       A  directive composed of one or more white-space characters is executed
       by reading input until no more valid input can be read, or  up  to  the
       first byte which is not a white-space character which remains unread.


       A  directive  that is an ordinary character is executed as follows. The
       next byte is read from the input and compared with the byte  that  com‐
       prises the directive; if the comparison shows that they are not equiva‐
       lent, the directive fails,  and  the  differing  and  subsequent  bytes
       remain unread.


       A  directive that is a conversion specification defines a set of match‐
       ing input sequences, as described below for each conversion  character.
       A conversion specification is executed in the following steps:


       Input white-space characters (as specified by isspace(3C)) are skipped,
       unless the conversion specification includes a [, c, C, or n conversion
       character.


       An  item  is  read  from  the input unless the conversion specification
       includes an n conversion character. The length of the item read is lim‐
       ited  to  any  specified  maximum  field width, which is interpreted in
       either characters or bytes depending on the  conversion  character.  In
       Solaris default mode, the input item is defined as the longest sequence
       of input bytes that forms a matching sequence. In some  cases,  scanf()
       might need to read several extra characters beyond the end of the input
       item to find the end of a matching sequence.  In  C99/SUSv3  mode,  the
       input  item  is defined as the longest sequence of input bytes that is,
       or is a prefix of, a matching sequence. With this  definition,  scanf()
       need  only read at most one character beyond the end of the input item.
       Therefore, in C99/SUSv3 mode, some sequences  that  are  acceptable  to
       strtod(3C),  strtol(3C),  and  similar  functions  are  unacceptable to
       scanf(). In either mode, scanf() attempts to push back any excess bytes
       read  using  ungetc(3C).  Assuming all such attempts succeed, the first
       byte, if any, after the input item remains unread. If the length of the
       input  item  is  0,  the conversion fails. This condition is a matching
       failure unless end-of-file, an encoding error, or  a  read  error  pre‐
       vented input from the stream, in which case it is an input failure.


       Except  in the case of a % conversion character, the input item (or, in
       the case of a %n conversion specification, the count of input bytes) is
       converted  to  a  type  appropriate to the conversion character. If the
       input item is not a matching sequence, the execution of the  conversion
       specification  fails;  this  condition  is  a  matching failure. Unless
       assignment suppression was indicated by a *, the result of the  conver‐
       sion is placed in the object pointed to by the first argument following
       the format argument that has not already received a  conversion  result
       if the conversion specification is introduced by %, or in the nth argu‐
       ment if introduced by the character sequence %n$. If this  object  does
       not have an appropriate type, or if the result of the conversion cannot
       be represented in the space provided, the behavior is undefined.

   Length Modifiers
       The length modifiers and their meanings are:

       hh              Specifies that a following d, i, o, u, x, X, or n  con‐
                       version  specifier  applies  to  an  argument with type
                       pointer to signed char or unsigned char.


       h               Specifies that a following d, i, o, u, x, X, or n  con‐
                       version  specifier  applies  to  an  argument with type
                       pointer to short or unsigned short.


       l (ell)         Specifies that a following d, i, o, u, x, X, or n  con‐
                       version  specifier  applies  to  an  argument with type
                       pointer to long or unsigned long; that a  following  a,
                       A,  e, E, f, F, g, or G conversion specifier applies to
                       an argument with type pointer to double; or that a fol‐
                       lowing  c,  s,  or [ conversion specifier applies to an
                       argument with type pointer to wchar_t.


       ll (ell-ell)    Specifies that a following d, i, o, u, x, X, or n  con‐
                       version  specifier  applies  to  an  argument with type
                       pointer to long long or unsigned long long.


       j               Specifies that a following d, i, o, u, x, X, or n  con‐
                       version  specifier  applies  to  an  argument with type
                       pointer to intmax_t or uintmax_t.


       z               Specifies that a following d, i, o, u, x, X, or n  con‐
                       version  specifier  applies  to  an  argument with type
                       pointer to size_t or the corresponding  signed  integer
                       type.


       t               Specifies  that a following d, i, o, u, x, X, or n con‐
                       version specifier applies  to  an  argument  with  type
                       pointer  to  ptrdiff_t  or  the  corresponding unsigned
                       type.


       L               Specifies that a following a, A, e, E, f, F,  g,  or  G
                       conversion  specifier  applies to an argument with type
                       pointer to long double.



       If a length modifier appears with any conversion specifier  other  than
       as specified above, the behavior is undefined.

   Conversion Characters
       The following conversion characters are valid:

       d          Matches  an  optionally signed decimal integer, whose format
                  is the same as expected for the  subject  sequence  of  str‐
                  tol(3C)  with  the  value  10  for the base argument. In the
                  absence of a size modifier, the corresponding argument  must
                  be a pointer to int.


       i          Matches  an  optionally  signed integer, whose format is the
                  same as expected for the subject sequence of strtol() with 0
                  for  the  base  argument. In the absence of a size modifier,
                  the corresponding argument must be a pointer to int.


       o          Matches an optionally signed octal integer, whose format  is
                  the same as expected for the subject sequence of strtoul(3C)
                  with the value 8 for the base argument. In the absence of  a
                  size  modifier, the corresponding argument must be a pointer
                  to unsigned int.


       u          Matches an optionally signed decimal integer,  whose  format
                  is  the  same  as  expected for the subject sequence of str‐
                  toul() with the value 10  for  the  base  argument.  In  the
                  absence  of a size modifier, the corresponding argument must
                  be a pointer to unsigned int.


       x          Matches an optionally signed hexadecimal integer, whose for‐
                  mat is the same as expected for the subject sequence of str‐
                  toul() with the value 16  for  the  base  argument.  In  the
                  absence  of a size modifier, the corresponding argument must
                  be a pointer to unsigned int.


       a,e,f,g    Matches an optionally signed floating-point  number,  infin‐
                  ity,  or  NaN,  whose format is the same as expected for the
                  subject sequence of strtod(3C). In the  absence  of  a  size
                  modifier,  the  corresponding  argument must be a pointer to
                  float. The e, f, and g specifiers match hexadecimal floating
                  point  values only in C99/SUSv3 (see standards(7)) mode, but
                  the a specifier always matches  hexadecimal  floating  point
                  values.

                  These  conversion  specifiers  match  any  subject  sequence
                  accepted by strtod(3C), including the  INF,  INFINITY,  NAN,
                  and NAN(n-char-sequence) forms. The result of the conversion
                  is the same as that of calling strtod() (or strtof() or str‐
                  told()) with the matching sequence, including the raising of
                  floating point  exceptions  and  the  setting  of  errno  to
                  ERANGE, if applicable.


       s          Matches a sequence of bytes that are not white-space charac‐
                  ters. The corresponding argument must be a  pointer  to  the
                  initial  byte  of an array of char, signed char, or unsigned
                  char large enough to accept the sequence and  a  terminating
                  null character code, which will be added automatically.

                  If  an l (ell) qualifier is present, the input is a sequence
                  of characters that begins in the initial shift  state.  Each
                  character  is  converted to a wide-character as if by a call
                  to the  mbrtowc(3C)  function,  with  the  conversion  state
                  described  by an mbstate_t object initialized to zero before
                  the first character is converted. The corresponding argument
                  must  be  a  pointer  to an array of wchar_t large enough to
                  accept the sequence and the terminating null wide-character,
                  which will be added automatically.


       [          Matches  a  non-empty  sequence  of characters from a set of
                  expected characters (the  scanset).  The  normal  skip  over
                  white-space  characters is suppressed in this case. The cor‐
                  responding argument must be a pointer to the initial byte of
                  an array of char, signed char, or unsigned char large enough
                  to accept the sequence and a terminating  null  byte,  which
                  will be added automatically.

                  If  an l (ell) qualifier is present, the input is a sequence
                  of characters that begins in the initial shift  state.  Each
                  character  in  the sequence is converted to a wide-character
                  as if by a call to the mbrtowc() function, with the  conver‐
                  sion  state  described by an mbstate_t object initialized to
                  zero before the first character  is  converted.  The  corre‐
                  sponding  argument  must be a pointer to an array of wchar_t
                  large enough to accept the sequence and the terminating null
                  wide-character, which will be added automatically.

                  The conversion specification includes all subsequent charac‐
                  ters in the format string up to and including  the  matching
                  right  square bracket (]). The characters between the square
                  brackets (the scanlist) comprise  the  scanset,  unless  the
                  character after the left square bracket is a circumflex (^),
                  in which case the scanset contains all  characters  that  do
                  not  appear  in  the scanlist between the circumflex and the
                  right square bracket. If the conversion specification begins
                  with  [] or [^], the right square bracket is included in the
                  scanlist and the next right square bracket is  the  matching
                  right square bracket that ends the conversion specification;
                  otherwise the first right square bracket  is  the  one  that
                  ends the conversion specification. If a - is in the scanlist
                  and is not the first character, nor  the  second  where  the
                  first character is a ^, nor the last character, it indicates
                  a range of characters to be matched.


       c          Matches a sequence of characters of the number specified  by
                  the  field width (1 if no field width is present in the con‐
                  version specification). The corresponding argument must be a
                  pointer  to  the  initial  byte  of an array of char, signed
                  char, or unsigned char large enough to accept the  sequence.
                  No  null  byte  is  added.  The normal skip over white-space
                  characters is suppressed in this case.

                  If an l (ell) qualifier is present, the input is a  sequence
                  of  characters  that begins in the initial shift state. Each
                  character in the sequence is converted to  a  wide-character
                  as  if by a call to the mbrtowc() function, with the conver‐
                  sion state described by an mbstate_t object  initialized  to
                  zero  before  the  first  character is converted. The corre‐
                  sponding argument must be a pointer to an array  of  wchar_t
                  large  enough to accept the resulting sequence of wide-char‐
                  acters. No null wide-character is added.


       p          Matches the set of sequences that is the same as the set  of
                  sequences  that is produced by the %p conversion of the cor‐
                  responding printf(3C) functions. The corresponding  argument
                  must be a pointer to a pointer to void. If the input item is
                  a value converted earlier during the same program execution,
                  the  pointer  that results will compare equal to that value;
                  otherwise the behavior of the %p conversion is undefined.


       n          No input is consumed. The corresponding argument must  be  a
                  pointer  to the integer into which is to be written the num‐
                  ber of bytes read from the input so far by this call to  the
                  scanf()  functions.  Execution of a %n conversion specifica‐
                  tion does not increment the assignment count returned at the
                  completion of execution of the function.


       C          Same as lc.


       S          Same as ls.


       %          Matches  a single %; no conversion or assignment occurs. The
                  complete conversion specification must be %%.



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


       The conversion characters A, E, F, G, and X are also valid  and  behave
       the same as, respectively, a, e, f, g, and x.


       If  end-of-file  is encountered during input, conversion is terminated.
       If end-of-file occurs before any bytes matching the current  conversion
       specification (except for %n) have been read (other than leading white-
       space characters, where permitted), execution of the current conversion
       specification  terminates with an input failure. Otherwise, unless exe‐
       cution of the current conversion specification  is  terminated  with  a
       matching  failure,  execution of the following conversion specification
       (if any) is terminated with an input failure.


       Reaching the end of the string in sscanf() is equivalent to  encounter‐
       ing end-of-file for fscanf().


       If conversion terminates on a conflicting input, the offending input is
       left unread in the input. Any trailing white space  (including  newline
       characters)  is  left  unread unless matched by a conversion specifica‐
       tion. The success of literal matches and suppressed assignments is only
       directly determinable via the %n conversion specification.


       The  fscanf()  and scanf() functions may mark the st_atime field of the
       file associated with stream for update.  The  st_atime  field  will  be
       marked  for  update  by  the  first  successful execution of fgetc(3C),
       fgets(3C), fread(3C), fscanf(),  getc(3C),  getdelim(3C),  getline(3C),
       getchar(3C),  gets(3C),  or  scanf() using stream that returns data not
       supplied by a prior call to ungetc(3C).

   C11 Bounds Checking Interfaces
       The scanf_s(), fscanf_s(),  sscanf_s(),  vscanf_s(),  vfscanf_s(),  and
       vsscanf_s()  functions  are  part of the C11 bounds checking interfaces
       specified in the C11 standard, Annex K. Each provide similar  function‐
       ality to the scanf(), fscanf(), sscanf(), vscanf(), vfscanf(), and vss‐
       canf() functions respectively, except  for  additional  checks  on  the
       parameters  passed  and  explicit runtime-constraints as defined in the
       C11 standard.  See  runtime_constraint_handler(3C)  and  INCITS/ISO/IEC
       9899:2011.

RETURN VALUES
       Upon  successful  completion, these functions return the number of suc‐
       cessfully matched and assigned input items; this number can be 0 in the
       event  of an early matching failure. If the input ends before the first
       matching failure or conversion, or if  a  runtime-constraint  violation
       occurs  in  fscanf_s(), scanf_s(), sscanf_s(), vscanf_s(), vfscanf_s(),
       or vsscanf_s(), EOF is returned. If a read error occurs the error indi‐
       cator for the stream is set, EOF is returned, and errno is set to indi‐
       cate the error.

ERRORS
       For the conditions under which the scanf() functions will fail and  may
       fail, refer to fgetc(3C) or fgetwc(3C).


       In addition, fscanf() and fscanf_s() may fail if:

       EILSEQ    Input byte sequence does not form a valid character.


       EINVAL    There are insufficient arguments.



       The  functions  fscanf_s(),  scanf_s(),  sscnaf_s(),  vscanf_s(),  vfs‐
       canf_s(), and vsscanf_s() may fail if:


       EINVAL    Null pointer is passed.



USAGE
       If the application calling the scanf() functions  has  any  objects  of
       type  wint_t  or  wchar_t, it must also include the header <wchar.h> to
       have these objects defined.

EXAMPLES
       Example 1 The call:


         int i, n; float x; char name[50];
         n = scanf("%d%f%49s", &i, &x, name);




       with the input line:


         25 54.32E-1 Hamster




       will assign to n the value 3, to i the value 25, to x the value  5.432,
       and name will contain the string Hamster.


       Example 2 The call:


         int i; float x; char name[50];
         (void) scanf("%2d%f%*d %49[0123456789]", &i, &x, name);




       with input:


         56789 0123 56a72




       will  assign  56 to i, 789.0 to x, skip 0123, and place the string 56\0
       in name. The next call to getchar(3C) will return the character a.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i)


       ATTRIBUTE TYPEATTRIBUTE VALUE _ CSIEnabled _ Interface StabilityCommit‐
       ted _ MT-LevelMT-Safe _ StandardSee standards(7).



       The  scanf(),  fscanf(),  sscanf(),  vscanf(), vfscanf(), and vsscanf()
       functions can be used safely in multithreaded applications.


       The scanf_s(), fscanf_s(),  sscanf_s(),  vscanf_s(),  vfscanf_s(),  and
       vsscanf_s() functions cannot be used safely in a multithreaded applica‐
       tion due to the runtime constraint handler. For more  information,  see
       the runtime_constraint_handler(3C) man page.

SEE ALSO
       fgetc(3C), fgets(3C), fgetwc(3C), fread(3C), getdelim(3C), getline(3C),
       isspace(3C), printf(3C), printf_s(3C), setlocale(3C), strtod(3C),  str‐
       tol(3C),  strtoul(3C),  wcrtomb(3C),  ungetc(3C),  attributes(7), stan‐
       dards(7), runtime_constraint_handler(3C)

WARNINGS
       The use of %s or %[ without length  modifiers  will  result  in  buffer
       overflows  if the input string contains a buffer longer than the memory
       allocation provided by the user.

NOTES
       The behavior of the conversion specifier %% has changed for all of  the
       functions  described  on  this manual page. Previously the %% specifier
       accepted a % character from input only if there were no preceding white
       space  characters. The new behavior accepts % even if there are preced‐
       ing white space characters. This  new  behavior  now  aligns  with  the
       description  on  this  manual page and in various standards. If the old
       behavior is desired, the conversion specification %*[%] can be used.



Oracle Solaris 11.4               11 Jun 2018                        scanf(3C)
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