The format is composed of zero or more directives: one or more white-space characters, an ordinary character (neither ?`%` ’ nor a white-space character), or a conversion specification.

###### Overview

Each conversion specification is introduced by the character ?`%` ’. After the ?`%` ’, the following appear in sequence:

- An optional assignment-suppressing character ?`*` ’.
- An optional nonzero decimal integer that specifies the maximum field width (in characters).
- An optional length modifier that specifies the size of the receiving object.
- A conversion specifier character that specifies the type of conversion to be applied.

The formatted input function executes each directive of the format in turn. If a directive fails, the function returns. Failures are described as input failures (because of the occurrence of an encoding error or the unavailability of input characters), or matching failures (because of inappropriate input).

A directive composed of white-space character(s) is executed by reading input up to the first non-white-space character (which remains unread), or until no more characters can be read.

A directive that is an ordinary character is executed by reading the next characters of the stream. If any of those characters differ from the ones composing the directive, the directive fails and the differing and subsequent characters remain unread. Similarly, if end-of-file, an encoding error, or a read error prevents a character from being read, the directive fails.

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

- Input white-space characters (as specified by the isspace function) are skipped, unless the specification includes a ?`[` ’, ?`c` ’, or ?`n` ’ specifier.
- An input item is read from the stream, unless the specification includes an n specifier. An input item is defined as the longest sequence of input characters which does not exceed any specified field width and which is, or is a prefix of, a matching input sequence. The first character, if any, after the input item remains unread. If the length of the input item is zero, the execution of the directive fails; this condition is a matching failure unless
  end-of-file, an encoding error, or a read error prevented input from the stream, in which case it is an input failure.
- Except in the case of a ?`%` ’ specifier, the input item (or, in the case of a %n directive, the count of input characters) is converted to a type appropriate to the conversion specifier. If the input item is not a matching sequence, the execution of the directive fails: this condition is a matching failure. Unless assignment suppression was indicated by a ?`*` ’, the result of the conversion is placed in the object pointed to by the first argument following the format argument that has not already received a conversion result. If this object does not have an appropriate type, or if the result of the conversion cannot be represented in the object, 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` ’ conversion specifier applies to an argument with type pointer to signed char or pointer to unsigned char.
? `h` ’
  Specifies that a following ? `d` ’, ? `i` ’, ? `o` ’, ? `u` ’, ? `x` ’, ? `X` ’, or ? `n` ’ conversion specifier applies to an argument with type pointer to short int or unsigned short int.
? `l` ’
  Specifies that a following ? `d` ’, ? `i` ’, ? `o` ’, ? `u` ’, ? `x` ’, ? `X` ’, or ? `n` ’ conversion specifier applies to an argument with type pointer to long int or unsigned long int; that a following ? `e` ’, ? `E` ’, ? `f` ’, ? `F` ’, ? `g` ’, or ? `G` ’ conversion specifier applies to an argument with type pointer to double. Some CrossWorks library variants do not support the ? `l` ’ length modifier in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Integer Support property of the project if you use this length modifier.
? `ll` ’
  Specifies that a following ? `d` ’, ? `i` ’, ? `o` ’, ? `u` ’, ? `x` ’, ? `X` ’, or ? `n` ’ conversion specifier applies to an argument with type pointer to long long int or unsigned long long int. Some CrossWorks library variants do not support the ? `ll` ’ length modifier in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Printf Integer Support property of the project if you use this length modifier.

If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined. Note that the C99 length modifiers ? `j` ’, ? `z` ’, ? `t` ’, and ? `L` ’ are not supported.

###### Conversion specifiers

? `d` ’
  Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of the strtol function with the value 10 for the base argument. The corresponding argument must be a pointer to signed integer.
? `i` ’
  Matches an optionally signed integer, whose format is the same as expected for the subject sequence of the strtol function with the value zero for the base argument. The corresponding argument must be a pointer to signed integer.
? `o` ’
  Matches an optionally signed octal integer, whose format is the same as expected for the subject sequence of the strtol function with the value 18 for the base argument. The corresponding argument must be a pointer to signed integer.
? `u` ’
  Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of the strtoul function with the value 10 for the base argument. The corresponding argument must be a pointer to unsigned integer.
? `x` ’
  Matches an optionally signed hexadecimal integer, whose format is the same as expected for the subject sequence of the strtoul function with the value 16 for the base argument. The corresponding argument must be a pointer to unsigned integer.
? `e` ’, ? `f` ’, ? `g` ’
  Matches an optionally signed floating-point number whose format is the same as expected for the subject sequence of the strtod function. The corresponding argument shall be a pointer to floating. Some CrossWorks library variants do not support the ? `e` ’, ? `f` ’ and ? `F` ’ conversion specifiers in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Scanf Floating Point Support property of the project if you use these conversion specifiers.
? `c` ’
  Matches a sequence of characters of exactly the number specified by the field width (one if no field width is present in the directive). The corresponding argument must be a pointer to the initial element of a character array large enough to accept the
  sequence. No null character is added.
? `s` ’
  Matches a sequence of non-white-space characters The corresponding argument must be a pointer to the initial element of a character array large enough to accept the sequence and a terminating null character, which will be added automatically.
? `[` ’
  Matches a nonempty sequence of characters from a set of expected characters (the scanset). The corresponding argument must be a pointer to the initial element of a character array large enough to accept the sequence and a terminating null character, which will be added automatically. The conversion specifier includes all subsequent characters in the format string, up to and including the matching right bracket ? `]` ’. The characters
  between the brackets (the scanlist) compose the scanset, unless the character after the left 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 bracket. If the conversion specifier begins with ? `[]` ’ or? `[^]` ’, the right bracket character is in the scanlist and the next following right bracket character is the matching right bracket that ends the specification; otherwise the first following right bracket character is the one that ends the specification. If a ? `-` ’ character is in the scanlist and is not the first, nor the second where the first character is a ? `^` ’, nor the last character, it is treated as a member of the scanset. Some CrossWorks library variants do not support the ? `[` ’ conversion specifier in order to reduce code and data space requirements; please ensure that you have selected the correct library in the Scanf Classes Supported property of the project if you use this conversion specifier.
? `p` ’
  Reads a sequence output by the corresponding ? `%p` ’ formatted output conversion. The corresponding argument must be a pointer to a pointer to void.
? `n` ’
  No input is consumed. The corresponding argument shall be a pointer to signed integer into which is to be written the number of characters read from the input stream so far by this call to the formatted input function. Execution of a ? `%n` ’ directive does not increment the assignment count returned at the completion of execution of the fscanf function. No argument is converted, but one is consumed. If the conversion specification includes an assignment-suppressing character or a field width, the behavior is undefined.
? `%` ’
  Matches a single ? `%` ’ character; no conversion or assignment occurs.

Note that the C99 width modifier ? `l` ’ used in conjuction with the ? `c` ’, ? `s` ’, and ? `[` ’ conversion specifiers is not supported and nor are the conversion specifiers ? `a` ’ and ? `A` ’.