221 lines
8.5 KiB
Plaintext
221 lines
8.5 KiB
Plaintext
'\"
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'\" Copyright (c) 1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" SCCS: @(#) format.n 1.10 96/03/25 20:15:25
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'\"
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.so man.macros
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.TH format n "" Tcl "Tcl Built-In Commands"
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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format \- Format a string in the style of sprintf
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.SH SYNOPSIS
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\fBformat \fIformatString \fR?\fIarg arg ...\fR?
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.BE
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.SH INTRODUCTION
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.PP
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This command generates a formatted string in the same way as the
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ANSI C \fBsprintf\fR procedure (it uses \fBsprintf\fR in its
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implementation).
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\fIFormatString\fR indicates how to format the result, using
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\fB%\fR conversion specifiers as in \fBsprintf\fR, and the additional
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arguments, if any, provide values to be substituted into the result.
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The return value from \fBformat\fR is the formatted string.
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.SH "DETAILS ON FORMATTING"
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.PP
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The command operates by scanning \fIformatString\fR from left to right.
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Each character from the format string is appended to the result
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string unless it is a percent sign.
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If the character is a \fB%\fR then it is not copied to the result string.
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Instead, the characters following the \fB%\fR character are treated as
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a conversion specifier.
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The conversion specifier controls the conversion of the next successive
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\fIarg\fR to a particular format and the result is appended to
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the result string in place of the conversion specifier.
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If there are multiple conversion specifiers in the format string,
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then each one controls the conversion of one additional \fIarg\fR.
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The \fBformat\fR command must be given enough \fIarg\fRs to meet the needs
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of all of the conversion specifiers in \fIformatString\fR.
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.PP
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Each conversion specifier may contain up to six different parts:
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.VS
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an XPG3 position specifier,
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.VE
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a set of flags, a minimum field width, a precision, a length modifier,
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and a conversion character.
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Any of these fields may be omitted except for the conversion character.
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The fields that are present must appear in the order given above.
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The paragraphs below discuss each of these fields in turn.
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.PP
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.VS
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If the \fB%\fR is followed by a decimal number and a \fB$\fR, as in
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``\fB%2$d\fR'', then the value to convert is not taken from the
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next sequential argument.
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Instead, it is taken from the argument indicated by the number,
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where 1 corresponds to the first \fIarg\fR.
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If the conversion specifier requires multiple arguments because
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of \fB*\fR characters in the specifier then
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successive arguments are used, starting with the argument
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given by the number.
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This follows the XPG3 conventions for positional specifiers.
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If there are any positional specifiers in \fIformatString\fR
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then all of the specifiers must be positional.
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.VE
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.PP
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The second portion of a conversion specifier may contain any of the
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following flag characters, in any order:
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.TP 10
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\fB\-\fR
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Specifies that the converted argument should be left-justified
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in its field (numbers are normally right-justified with leading
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spaces if needed).
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.TP 10
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\fB+\fR
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Specifies that a number should always be printed with a sign,
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even if positive.
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.TP 10
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\fIspace\fR
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Specifies that a space should be added to the beginning of the
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number if the first character isn't a sign.
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.TP 10
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\fB0\fR
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Specifies that the number should be padded on the left with
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zeroes instead of spaces.
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.TP 10
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\fB#\fR
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Requests an alternate output form. For \fBo\fR and \fBO\fR
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conversions it guarantees that the first digit is always \fB0\fR.
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For \fBx\fR or \fBX\fR conversions, \fB0x\fR or \fB0X\fR (respectively)
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will be added to the beginning of the result unless it is zero.
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For all floating-point conversions (\fBe\fR, \fBE\fR, \fBf\fR,
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\fBg\fR, and \fBG\fR) it guarantees that the result always
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has a decimal point.
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For \fBg\fR and \fBG\fR conversions it specifies that
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trailing zeroes should not be removed.
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.PP
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The third portion of a conversion specifier is a number giving a
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minimum field width for this conversion.
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It is typically used to make columns line up in tabular printouts.
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If the converted argument contains fewer characters than the
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minimum field width then it will be padded so that it is as wide
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as the minimum field width.
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Padding normally occurs by adding extra spaces on the left of the
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converted argument, but the \fB0\fR and \fB\-\fR flags
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may be used to specify padding with zeroes on the left or with
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spaces on the right, respectively.
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If the minimum field width is specified as \fB*\fR rather than
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a number, then the next argument to the \fBformat\fR command
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determines the minimum field width; it must be a numeric string.
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.PP
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The fourth portion of a conversion specifier is a precision,
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which consists of a period followed by a number.
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The number is used in different ways for different conversions.
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For \fBe\fR, \fBE\fR, and \fBf\fR conversions it specifies the number
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of digits to appear to the right of the decimal point.
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For \fBg\fR and \fBG\fR conversions it specifies the total number
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of digits to appear, including those on both sides of the decimal
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point (however, trailing zeroes after the decimal point will still
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be omitted unless the \fB#\fR flag has been specified).
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For integer conversions, it specifies a minimum number of digits
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to print (leading zeroes will be added if necessary).
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For \fBs\fR conversions it specifies the maximum number of characters to be
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printed; if the string is longer than this then the trailing characters will be dropped.
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If the precision is specified with \fB*\fR rather than a number
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then the next argument to the \fBformat\fR command determines the precision;
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it must be a numeric string.
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.PP
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The fifth part of a conversion specifier is a length modifier,
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which must be \fBh\fR or \fBl\fR.
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If it is \fBh\fR it specifies that the numeric value should be
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truncated to a 16-bit value before converting.
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This option is rarely useful.
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The \fBl\fR modifier is ignored.
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.PP
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The last thing in a conversion specifier is an alphabetic character
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that determines what kind of conversion to perform.
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The following conversion characters are currently supported:
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.TP 10
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\fBd\fR
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Convert integer to signed decimal string.
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.TP 10
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\fBu\fR
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Convert integer to unsigned decimal string.
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.TP 10
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\fBi\fR
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Convert integer to signed decimal string; the integer may either be
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in decimal, in octal (with a leading \fB0\fR) or in hexadecimal
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(with a leading \fB0x\fR).
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.TP 10
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\fBo\fR
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Convert integer to unsigned octal string.
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.TP 10
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\fBx\fR or \fBX\fR
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Convert integer to unsigned hexadecimal string, using digits
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``0123456789abcdef'' for \fBx\fR and ``0123456789ABCDEF'' for \fBX\fR).
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.TP 10
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\fBc\fR
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Convert integer to the 8-bit character it represents.
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.TP 10
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\fBs\fR
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No conversion; just insert string.
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.TP 10
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\fBf\fR
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Convert floating-point number to signed decimal string of
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the form \fIxx.yyy\fR, where the number of \fIy\fR's is determined by
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the precision (default: 6).
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If the precision is 0 then no decimal point is output.
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.TP 10
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\fBe\fR or \fBe\fR
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Convert floating-point number to scientific notation in the
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form \fIx.yyy\fBe\(+-\fIzz\fR, where the number of \fIy\fR's is determined
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by the precision (default: 6).
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If the precision is 0 then no decimal point is output.
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If the \fBE\fR form is used then \fBE\fR is
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printed instead of \fBe\fR.
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.TP 10
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\fBg\fR or \fBG\fR
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If the exponent is less than \-4 or greater than or equal to the
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precision, then convert floating-point number as for \fB%e\fR or
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\fB%E\fR.
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Otherwise convert as for \fB%f\fR.
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Trailing zeroes and a trailing decimal point are omitted.
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.TP 10
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\fB%\fR
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No conversion: just insert \fB%\fR.
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.LP
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For the numerical conversions the argument being converted must
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be an integer or floating-point string; format converts the argument
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to binary and then converts it back to a string according to
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the conversion specifier.
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.SH "DIFFERENCES FROM ANSI SPRINTF"
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.PP
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.VS
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The behavior of the format command is the same as the
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ANSI C \fBsprintf\fR procedure except for the following
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differences:
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.IP [1]
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\fB%p\fR and \fB%n\fR specifiers are not currently supported.
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.VE
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.IP [2]
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For \fB%c\fR conversions the argument must be a decimal string,
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which will then be converted to the corresponding character value.
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.IP [3]
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.VS
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The \fBl\fR modifier is ignored; integer values are always converted
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as if there were no modifier present and real values are always
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converted as if the \fBl\fR modifier were present (i.e. type
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\fBdouble\fR is used for the internal representation).
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If the \fBh\fR modifier is specified then integer values are truncated
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to \fBshort\fR before conversion.
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.VE
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.SH KEYWORDS
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conversion specifier, format, sprintf, string, substitution
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