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(require 'stdio)
requires printf and scanf and additionally defines
the symbols:
Defined to be (current-input-port).
Defined to be (current-output-port).
Defined to be (current-error-port).
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(require 'printf)
Each function converts, formats, and outputs its arg1 … arguments according to the control string format argument and returns the number of characters output.
printf sends its output to the port (current-output-port).
fprintf sends its output to the port port. sprintf
string-set!s locations of the non-constant string argument
str to the output characters.
Two extensions of sprintf return new strings. If the first
argument is #f, then the returned string’s length is as many
characters as specified by the format and data; if the first
argument is a non-negative integer k, then the length of the
returned string is also bounded by k.
The string format contains plain characters which are copied to the output stream, and conversion specifications, each of which results in fetching zero or more of the arguments arg1 …. The results are undefined if there are an insufficient number of arguments for the format. If format is exhausted while some of the arg1 … arguments remain unused, the excess arg1 … arguments are ignored.
The conversion specifications in a format string have the form:
% [ flags ] [ width ] [ . precision ] [ type ] conversion
An output conversion specifications consist of an initial ‘%’ character followed in sequence by:
Left-justify the result in the field. Normally the result is right-justified.
For the signed ‘%d’ and ‘%i’ conversions and all inexact conversions, prefix a plus sign if the value is positive.
For the signed ‘%d’ and ‘%i’ conversions, if the result doesn’t start with a plus or minus sign, prefix it with a space character instead. Since the ‘+’ flag ensures that the result includes a sign, this flag is ignored if both are specified.
For inexact conversions, ‘#’ specifies that the result should always include a decimal point, even if no digits follow it. For the ‘%g’ and ‘%G’ conversions, this also forces trailing zeros after the decimal point to be printed where they would otherwise be elided.
For the ‘%o’ conversion, force the leading digit to be ‘0’, as
if by increasing the precision. For ‘%x’ or ‘%X’, prefix a
leading ‘0x’ or ‘0X’ (respectively) to the result. This
doesn’t do anything useful for the ‘%d’, ‘%i’, or ‘%u’
conversions. Using this flag produces output which can be parsed by the
scanf functions with the ‘%i’ conversion
(see Standard Formatted Input).
Pad the field with zeros instead of spaces. The zeros are placed after any indication of sign or base. This flag is ignored if the ‘-’ flag is also specified, or if a precision is specified for an exact converson.
Alternatively, if the field width is ‘*’, the next argument in the argument list (before the actual value to be printed) is used as the field width. The width value must be an integer. If the value is negative it is as though the ‘-’ flag is set (see above) and the absolute value is used as the field width.
Alternatively, if the precision is ‘.*’, the next argument in the argument list (before the actual value to be printed) is used as the precision. The value must be an integer, and is ignored if negative. If you specify ‘*’ for both the field width and precision, the field width argument precedes the precision argument. The ‘.*’ precision is an enhancement. C library versions may not accept this syntax.
For the ‘%f’, ‘%e’, and ‘%E’ conversions, the precision
specifies how many digits follow the decimal-point character. The
default precision is 6. If the precision is explicitly 0,
the decimal point character is suppressed.
For the ‘%g’ and ‘%G’ conversions, the precision specifies how
many significant digits to print. Significant digits are the first
digit before the decimal point, and all the digits after it. If the
precision is 0 or not specified for ‘%g’ or ‘%G’, it is
treated like a value of 1. If the value being printed cannot be
expressed accurately in the specified number of digits, the value is
rounded to the nearest number that fits.
For exact conversions, if a precision is supplied it specifies the minimum number of digits to appear; leading zeros are produced if necessary. If a precision is not supplied, the number is printed with as many digits as necessary. Converting an exact ‘0’ with an explicit precision of zero produces no characters.
Exact Conversions
Print an integer as an unsigned binary number.
Note: ‘%b’ and ‘%B’ are SLIB extensions.
Print an integer as a signed decimal number. ‘%d’ and ‘%i’
are synonymous for output, but are different when used with scanf
for input (see Standard Formatted Input).
Print an integer as an unsigned octal number.
Print an integer as an unsigned decimal number.
Print an integer as an unsigned hexadecimal number. ‘%x’ prints using the digits ‘0123456789abcdef’. ‘%X’ prints using the digits ‘0123456789ABCDEF’.
Inexact Conversions
Print a floating-point number in fixed-point notation.
Print a floating-point number in exponential notation. ‘%e’ prints ‘e’ between mantissa and exponont. ‘%E’ prints ‘E’ between mantissa and exponont.
Print a floating-point number in either fixed or exponential notation, whichever is more appropriate for its magnitude. Unless an ‘#’ flag has been supplied, trailing zeros after a decimal point will be stripped off. ‘%g’ prints ‘e’ between mantissa and exponont. ‘%G’ prints ‘E’ between mantissa and exponent.
Print a number like ‘%g’, except that an SI prefix is output after the number, which is scaled accordingly. ‘%K’ outputs a dot between number and prefix, ‘%k’ does not.
Other Conversions
Print a single character. The ‘-’ flag is the only one which can be specified. It is an error to specify a precision.
Print a string. The ‘-’ flag is the only one which can be specified. A precision specifies the maximum number of characters to output; otherwise all characters in the string are output.
Print a scheme expression. The ‘-’ flag left-justifies the output.
The ‘#’ flag specifies that strings and characters should be quoted
as by write (which can be read using read); otherwise,
output is as display prints. A precision specifies the maximum
number of characters to output; otherwise as many characters as needed
are output.
Note: ‘%a’ and ‘%A’ are SLIB extensions.
Print a literal ‘%’ character. No argument is consumed. It is an error to specify flags, field width, precision, or type modifiers with ‘%%’.
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(require 'scanf)
Each function reads characters, interpreting them according to the control string format argument.
scanf-read-list returns a list of the items specified as far as
the input matches format. scanf, fscanf, and
sscanf return the number of items successfully matched and
stored. scanf, fscanf, and sscanf also set the
location corresponding to arg1 … using the methods:
set!
set-car!
set-cdr!
vector-set!
substring-move-left!
The argument to a substring expression in arg1 … must
be a non-constant string. Characters will be stored starting at the
position specified by the second argument to substring. The
number of characters stored will be limited by either the position
specified by the third argument to substring or the length of the
matched string, whichever is less.
The control string, format, contains conversion specifications and other characters used to direct interpretation of input sequences. The control string contains:
Unless the specification contains the ‘n’ conversion character (described below), a conversion specification directs the conversion of the next input field. The result of a conversion specification is returned in the position of the corresponding argument points, unless ‘*’ indicates assignment suppression. Assignment suppression provides a way to describe an input field to be skipped. An input field is defined as a string of characters; it extends to the next inappropriate character or until the field width, if specified, is exhausted.
Note: This specification of format strings differs from the ANSI C and POSIX specifications. In SLIB, white space before an input field is not skipped unless white space appears before the conversion specification in the format string. In order to write format strings which work identically with ANSI C and SLIB, prepend whitespace to all conversion specifications except ‘[’ and ‘c’.
The conversion code indicates the interpretation of the input field; For a suppressed field, no value is returned. The following conversion codes are legal:
A single % is expected in the input at this point; no value is returned.
A decimal integer is expected.
An unsigned decimal integer is expected.
An octal integer is expected.
A hexadecimal integer is expected.
An integer is expected. Returns the value of the next input item, interpreted according to C conventions; a leading ‘0’ implies octal, a leading ‘0x’ implies hexadecimal; otherwise, decimal is assumed.
Returns the total number of bytes (including white space) read by
scanf. No input is consumed by %n.
A floating-point number is expected. The input format for floating-point numbers is an optionally signed string of digits, possibly containing a radix character ‘.’, followed by an optional exponent field consisting of an ‘E’ or an ‘e’, followed by an optional ‘+’, ‘-’, or space, followed by an integer.
Width characters are expected. The normal skip-over-white-space is suppressed in this case; to read the next non-space character, use ‘%1s’. If a field width is given, a string is returned; up to the indicated number of characters is read.
A character string is expected The input field is terminated by a
white-space character. scanf cannot read a null string.
Indicates string data and the normal skip-over-leading-white-space is suppressed. The left bracket is followed by a set of characters, called the scanset, and a right bracket; the input field is the maximal sequence of input characters consisting entirely of characters in the scanset. ‘^’, when it appears as the first character in the scanset, serves as a complement operator and redefines the scanset as the set of all characters not contained in the remainder of the scanset string. Construction of the scanset follows certain conventions. A range of characters may be represented by the construct first-last, enabling ‘[0123456789]’ to be expressed ‘[0-9]’. Using this convention, first must be lexically less than or equal to last; otherwise, the dash stands for itself. The dash also stands for itself when it is the first or the last character in the scanset. To include the right square bracket as an element of the scanset, it must appear as the first character (possibly preceded by a ‘^’) of the scanset, in which case it will not be interpreted syntactically as the closing bracket. At least one character must match for this conversion to succeed.
The scanf functions terminate their conversions at end-of-file,
at the end of the control string, or when an input character conflicts
with the control string. In the latter case, the offending character is
left unread in the input stream.
Next: Program and Arguments, Previous: Format (version 3.1), Up: Textual Conversion Packages [Contents][Index]