sscanf()

#include <stdio.h>

  

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

  

sscanf() scans string s according to the given format, storing the values in the given parameters. The format specifiers in the format tell sscanf() what to expect next. A format specifier has the format:

• FormatSpec = %[Flag][Width][Size]Conversion

  where:

  • Flag = *

    If the % sign, which starts a format specification, is followed by a *, the scanned value is not assigned to the corresponding parameter.

  • Width = Number

    Specifies the maximum number of characters to read when scanning the value. Scanning also stops if white space or a character not matching the expected syntax is reached.

  • Size = h|l|L

    Specifies the size of the argument to read. The following table describes the meaning of the size argument.

    Table 1. Relationship of the Size Parameter with Allowable Conversions and Types

    Size	Allowable Conversions	Parameter Type
    h	d, i, n	short int * (instead of int *)
    h	o, u, x, X	unsigned short int * (instead of unsigned int *)
    l	d, i, n	long int * (instead of int *)
    l	o, u, x, X	unsigned long int * (instead of unsigned int *)
    l	e, E, f, g, G	double * (instead of float *)
    L	e, E, f, g, G	long double * (instead of float *)

  • Conversion = c|d|e|E|f|g|G|i|n|o|p|s|u|x|X|%|Range

    These conversion characters tell sscanf() what to read and how to store it in a parameter. Their meaning is shown in the following table.

    Table 2. Actions Taken for Conversions

    Conversion	Description
    c	Reads a string of exactly width characters and stores it in the parameter. If no width is given, reads one character. The argument must be a char *. The string read is not zero-terminated.
    d	Reads as a decimal number (syntax below) and stores in the parameter. The parameter must be a pointer to an integral type.
    i	Reads as d (above), but also reads octal and hexadecimal numbers (syntax below).
    e, E, f, g, or G	Reads a floating-point number (syntax below). The parameter must be a pointer to a floating-point type.
    n	The argument must be a pointer to an int. sscanf() writes the number of characters read so far to that address. If n is used together with length specifier h or l, the argument must be a pointer to a shortint or a longint.
    o	Reads an octal number (syntax below). The parameter must be a pointer to an integral type.
    p	Reads a pointer in the same format as sprintf() prints it. The parameter must be a void **.
    s	Reads a character string up to the next white space character or at most width characters. The string is zero-terminated. The argument must be of type char *.
    u	Reads as d (above), but the parameter must be a pointer to an unsigned integral type.
    x, X	Reads as u (above), but reads a hexadecimal number.
    %	Skips a % sign in the input. Give only as %%.

      Range = [[^]List] 
      

      List = Element {Element} 
      

      Element = <any char> [-<any char>] 
      

You can also use a scan set to read a character string that either contains only the given characters or contains only characters not in the set. A scan set always is bracketed by left and right brackets. If the first character in the set is ^, the set is inverted (that is, only characters not in the set are allowed). You can specify whole character ranges, (for example, A-Z specifies all upper-case letters). To include a right bracket in the scan set, it must be the first element in the list; a dash ( -) must be either the first or the last element. To include a ^ in the list (instead of indicating an inverted list) ensure that the ^ is not the first character after the left bracket.

Some examples are:

[A-Za-z] Allows all upper- and lower-case characters.

[^A-Z] Allows any character that is not an upper-case character.

[]abc] Allows ], a, b and c.

[^]abc] Allows any character except ], a, b and c.

[-abc] Allows -, a, b and c.

A white space in the format string skips all white space characters up to the next non-white-space character. Any other character in the format must be exactly matched by the input; otherwise sscanf() stops scanning.

The syntax for numbers as scanned by sscanf() is the following:

  Number = FloatNumber|IntNumber 
  

  IntNumber = DecNumber|OctNumber|HexNumber 
  

  DecNumber = SignDigit{Digit} 
  

  OctNumber = Sign0{OctDigit} 
  

  HexNumber = 0(x|X) HexDigit {HexDigit} 
  

  FloatNumber = Sign {Digit} [.{Digit}] [Exponent] 
  

  Exponent = (e|E)DecNumber 
  

  OctDigit = 0|1|2|3|4|5|6|7 
  

  Digit = OctDigit|8|9 
  

  HexDigit = Digit |A|B|C|D|E|F|a|b|c|d|e|f 
  

EOF, if s is NULL; otherwise it returns the number of arguments filled in.