381 lines
19 KiB
HTML
381 lines
19 KiB
HTML
<HTML><HEAD><TITLE>Tcl Built-In Commands - expr manual page</TITLE></HEAD><BODY>
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<DL>
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<DD><A HREF="expr.htm#M2" NAME="L238">NAME</A>
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<DL><DD>expr - Evaluate an expression</DL>
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<DD><A HREF="expr.htm#M3" NAME="L239">SYNOPSIS</A>
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<DL>
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<DD><B>expr </B><I>arg </I>?<I>arg arg ...</I>?
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</DL>
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<DD><A HREF="expr.htm#M4" NAME="L240">DESCRIPTION</A>
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<DD><A HREF="expr.htm#M5" NAME="L241">OPERANDS</A>
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<DL>
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</DL>
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<DD><A HREF="expr.htm#M6" NAME="L242">OPERATORS</A>
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<DL>
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<DD><A HREF="expr.htm#M7" NAME="L243"><B>- + ~ !</B></A>
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<DD><A HREF="expr.htm#M8" NAME="L244"><B>* / %</B></A>
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<DD><A HREF="expr.htm#M9" NAME="L245"><B>+ -</B></A>
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<DD><A HREF="expr.htm#M10" NAME="L246"><B><< >></B></A>
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<DD><A HREF="expr.htm#M11" NAME="L247"><B>< > <= >=</B></A>
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<DD><A HREF="expr.htm#M12" NAME="L248"><B>== !=</B></A>
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<DD><A HREF="expr.htm#M13" NAME="L249"><B>&</B></A>
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<DD><A HREF="expr.htm#M14" NAME="L250"><B>^</B></A>
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<DD><A HREF="expr.htm#M15" NAME="L251"><B>|</B></A>
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<DD><A HREF="expr.htm#M16" NAME="L252"><B>&&</B></A>
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<DD><A HREF="expr.htm#M17" NAME="L253"><B>||</B></A>
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<DD><A HREF="expr.htm#M18" NAME="L254"><I>x</I><B>?</B><I>y</I><B>:</B><I>z</I></A>
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</DL>
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<DD><A HREF="expr.htm#M19" NAME="L255">MATH FUNCTIONS</A>
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<DL>
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<DD><A HREF="expr.htm#M20" NAME="L256"><B>abs(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M21" NAME="L257"><B>acos(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M22" NAME="L258"><B>asin(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M23" NAME="L259"><B>atan(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M24" NAME="L260"><B>atan2(</B><I>x, y</I><B>)</B></A>
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<DD><A HREF="expr.htm#M25" NAME="L261"><B>ceil(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M26" NAME="L262"><B>cos(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M27" NAME="L263"><B>cosh(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M28" NAME="L264"><B>double(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M29" NAME="L265"><B>exp(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M30" NAME="L266"><B>floor(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M31" NAME="L267"><B>fmod(</B><I>x, y</I><B>)</B></A>
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<DD><A HREF="expr.htm#M32" NAME="L268"><B>hypot(</B><I>x, y</I><B>)</B></A>
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<DD><A HREF="expr.htm#M33" NAME="L269"><B>int(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M34" NAME="L270"><B>log(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M35" NAME="L271"><B>log10(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M36" NAME="L272"><B>pow(</B><I>x, y</I><B>)</B></A>
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<DD><A HREF="expr.htm#M37" NAME="L273"><B>rand()</B></A>
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<DD><A HREF="expr.htm#M38" NAME="L274"><B>round(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M39" NAME="L275"><B>sin(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M40" NAME="L276"><B>sinh(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M41" NAME="L277"><B>sqrt(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M42" NAME="L278"><B>srand(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M43" NAME="L279"><B>tan(</B><I>arg</I><B>)</B></A>
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<DD><A HREF="expr.htm#M44" NAME="L280"><B>tanh(</B><I>arg</I><B>)</B></A>
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</DL>
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<DD><A HREF="expr.htm#M45" NAME="L281">TYPES, OVERFLOW, AND PRECISION</A>
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<DD><A HREF="expr.htm#M46" NAME="L282">STRING OPERATIONS</A>
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<DD><A HREF="expr.htm#M47" NAME="L283">PERFORMANCE CONSIDERATIONS</A>
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<DD><A HREF="expr.htm#M48" NAME="L284">KEYWORDS</A>
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</DL><HR>
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<H3><A NAME="M2">NAME</A></H3>
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expr - Evaluate an expression
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<H3><A NAME="M3">SYNOPSIS</A></H3>
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<B>expr </B><I>arg </I>?<I>arg arg ...</I>?<BR>
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<H3><A NAME="M4">DESCRIPTION</A></H3>
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Concatenates <I>arg</I>'s (adding separator spaces between them),
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evaluates the result as a Tcl expression, and returns the value.
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The operators permitted in Tcl expressions are a subset of
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the operators permitted in C expressions, and they have the
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same meaning and precedence as the corresponding C operators.
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Expressions almost always yield numeric results
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(integer or floating-point values).
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For example, the expression
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<PRE><B>expr 8.2 + 6</B></PRE>
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evaluates to 14.2.
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Tcl expressions differ from C expressions in the way that
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operands are specified. Also, Tcl expressions support
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non-numeric operands and string comparisons.
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<H3><A NAME="M5">OPERANDS</A></H3>
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A Tcl expression consists of a combination of operands, operators,
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and parentheses.
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White space may be used between the operands and operators and
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parentheses; it is ignored by the expression's instructions.
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Where possible, operands are interpreted as integer values.
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Integer values may be specified in decimal (the normal case), in octal (if the
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first character of the operand is <B>0</B>), or in hexadecimal (if the first
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two characters of the operand are <B>0x</B>).
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If an operand does not have one of the integer formats given
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above, then it is treated as a floating-point number if that is
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possible. Floating-point numbers may be specified in any of the
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ways accepted by an ANSI-compliant C compiler (except that the
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<B>f</B>, <B>F</B>, <B>l</B>, and <B>L</B> suffixes will not be permitted in
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most installations). For example, all of the
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following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16.
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If no numeric interpretation is possible, then an operand is left
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as a string (and only a limited set of operators may be applied to
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it).
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<P>
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Operands may be specified in any of the following ways:
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<P>
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<DL>
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<P><DT>[1]<DD>
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As an numeric value, either integer or floating-point.
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<P><DT>[2]<DD>
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As a Tcl variable, using standard <B>$</B> notation.
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The variable's value will be used as the operand.
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<P><DT>[3]<DD>
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As a string enclosed in double-quotes.
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The expression parser will perform backslash, variable, and
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command substitutions on the information between the quotes,
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and use the resulting value as the operand
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<P><DT>[4]<DD>
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As a string enclosed in braces.
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The characters between the open brace and matching close brace
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will be used as the operand without any substitutions.
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<P><DT>[5]<DD>
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As a Tcl command enclosed in brackets.
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The command will be executed and its result will be used as
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the operand.
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<P><DT>[6]<DD>
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As a mathematical function whose arguments have any of the above
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forms for operands, such as <B>sin($x)</B>. See below for a list of defined
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functions.
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<P></DL>
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<P>
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Where substitutions occur above (e.g. inside quoted strings), they
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are performed by the expression's instructions.
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However, an additional layer of substitution may already have
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been performed by the command parser before the expression
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processor was called.
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As discussed below, it is usually best to enclose expressions
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in braces to prevent the command parser from performing substitutions
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on the contents.
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<P>
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For some examples of simple expressions, suppose the variable
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<B>a</B> has the value 3 and
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the variable <B>b</B> has the value 6.
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Then the command on the left side of each of the lines below
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will produce the value on the right side of the line:
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<PRE><B>expr 3.1 + $a 6.1
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expr 2 + "$a.$b" 5.6
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expr 4*[llength "6 2"] 8
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expr {{word one} < "word $a"} 0</B></PRE>
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<H3><A NAME="M6">OPERATORS</A></H3>
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The valid operators are listed below, grouped in decreasing order
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of precedence:
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<P>
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<DL>
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<P><DT><A NAME="M7"><B>- + ~ !</B></A><DD>
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Unary minus, unary plus, bit-wise NOT, logical NOT. None of these operands
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may be applied to string operands, and bit-wise NOT may be
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applied only to integers.
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<P><DT><A NAME="M8"><B>* / %</B></A><DD>
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Multiply, divide, remainder. None of these operands may be
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applied to string operands, and remainder may be applied only
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to integers.
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The remainder will always have the same sign as the divisor and
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an absolute value smaller than the divisor.
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<P><DT><A NAME="M9"><B>+ -</B></A><DD>
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Add and subtract. Valid for any numeric operands.
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<P><DT><A NAME="M10"><B><< >></B></A><DD>
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Left and right shift. Valid for integer operands only.
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A right shift always propagates the sign bit.
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<P><DT><A NAME="M11"><B>< > <= >=</B></A><DD>
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Boolean less, greater, less than or equal, and greater than or equal.
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Each operator produces 1 if the condition is true, 0 otherwise.
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These operators may be applied to strings as well as numeric operands,
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in which case string comparison is used.
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<P><DT><A NAME="M12"><B>== !=</B></A><DD>
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Boolean equal and not equal. Each operator produces a zero/one result.
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Valid for all operand types.
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<P><DT><A NAME="M13"><B>&</B></A><DD>
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Bit-wise AND. Valid for integer operands only.
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<P><DT><A NAME="M14"><B>^</B></A><DD>
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Bit-wise exclusive OR. Valid for integer operands only.
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<P><DT><A NAME="M15"><B>|</B></A><DD>
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Bit-wise OR. Valid for integer operands only.
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<P><DT><A NAME="M16"><B>&&</B></A><DD>
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Logical AND. Produces a 1 result if both operands are non-zero,
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0 otherwise.
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Valid for boolean and numeric (integers or floating-point) operands only.
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<P><DT><A NAME="M17"><B>||</B></A><DD>
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Logical OR. Produces a 0 result if both operands are zero, 1 otherwise.
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Valid for boolean and numeric (integers or floating-point) operands only.
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<P><DT><A NAME="M18"><I>x</I><B>?</B><I>y</I><B>:</B><I>z</I></A><DD>
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If-then-else, as in C. If <I>x</I>
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evaluates to non-zero, then the result is the value of <I>y</I>.
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Otherwise the result is the value of <I>z</I>.
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The <I>x</I> operand must have a numeric value.
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<P></DL>
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<P>
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See the C manual for more details on the results
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produced by each operator.
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All of the binary operators group left-to-right within the same
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precedence level. For example, the command
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<PRE><B>expr 4*2 < 7</B></PRE>
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returns 0.
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<P>
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The <B>&&</B>, <B>||</B>, and <B>?:</B> operators have ``lazy
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evaluation'', just as in C,
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which means that operands are not evaluated if they are
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not needed to determine the outcome. For example, in the command
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<PRE><B>expr {$v ? [a] : [b]}</B></PRE>
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only one of <B>[a]</B> or <B>[b]</B> will actually be evaluated,
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depending on the value of <B>$v</B>. Note, however, that this is
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only true if the entire expression is enclosed in braces; otherwise
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the Tcl parser will evaluate both <B>[a]</B> and <B>[b]</B> before
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invoking the <B>expr</B> command.
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<H3><A NAME="M19">MATH FUNCTIONS</A></H3>
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Tcl supports the following mathematical functions in expressions:
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<PRE><B>abs</B> <B>cosh</B> <B>log</B> <B>sqrt</B>
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<B>acos</B> <B>double</B> <B>log10</B> <B>srand</B>
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<B>asin</B> <B>exp</B> <B>pow</B> <B>tan</B>
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<B>atan</B> <B>floor</B> <B>rand</B> <B>tanh</B>
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<B>atan2</B> <B>fmod</B> <B>round</B>
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<B>ceil</B> <B>hypot</B> <B>sin</B>
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<B>cos</B> <B>int</B> <B>sinh</B></PRE>
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<P>
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<P>
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<DL>
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<P><DT><A NAME="M20"><B>abs(</B><I>arg</I><B>)</B></A><DD>
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Returns the absolute value of <I>arg</I>. <I>Arg</I> may be either
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integer or floating-point, and the result is returned in the same form.
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<P><DT><A NAME="M21"><B>acos(</B><I>arg</I><B>)</B></A><DD>
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Returns the arc cosine of <I>arg</I>, in the range [0,pi]
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radians. <I>Arg</I> should be in the range [-1,1].
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<P><DT><A NAME="M22"><B>asin(</B><I>arg</I><B>)</B></A><DD>
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Returns the arc sine of <I>arg</I>, in the range [-pi/2,pi/2] radians.
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<I>Arg</I> should be in the range [-1,1].
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<P><DT><A NAME="M23"><B>atan(</B><I>arg</I><B>)</B></A><DD>
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Returns the arc tangent of <I>arg</I>, in the range [-pi/2,pi/2] radians.
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<P><DT><A NAME="M24"><B>atan2(</B><I>x, y</I><B>)</B></A><DD>
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Returns the arc tangent of <I>y</I>/<I>x</I>, in the range [-pi,pi]
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radians. <I>x</I> and <I>y</I> cannot both be 0.
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<P><DT><A NAME="M25"><B>ceil(</B><I>arg</I><B>)</B></A><DD>
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Returns the smallest integer value not less than <I>arg</I>.
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<P><DT><A NAME="M26"><B>cos(</B><I>arg</I><B>)</B></A><DD>
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Returns the cosine of <I>arg</I>, measured in radians.
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<P><DT><A NAME="M27"><B>cosh(</B><I>arg</I><B>)</B></A><DD>
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Returns the hyperbolic cosine of <I>arg</I>. If the result would cause
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an overflow, an error is returned.
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<P><DT><A NAME="M28"><B>double(</B><I>arg</I><B>)</B></A><DD>
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If <I>arg</I> is a floating value, returns <I>arg</I>, otherwise converts
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<I>arg</I> to floating and returns the converted value.
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<P><DT><A NAME="M29"><B>exp(</B><I>arg</I><B>)</B></A><DD>
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Returns the exponential of <I>arg</I>, defined as e**<I>arg</I>. If the
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result would cause an overflow, an error is returned.
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<P><DT><A NAME="M30"><B>floor(</B><I>arg</I><B>)</B></A><DD>
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Returns the largest integral value not greater than <I>arg</I>.
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<P><DT><A NAME="M31"><B>fmod(</B><I>x, y</I><B>)</B></A><DD>
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Returns the floating-point remainder of the division of <I>x</I> by
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<I>y</I>. If <I>y</I> is 0, an error is returned.
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<P><DT><A NAME="M32"><B>hypot(</B><I>x, y</I><B>)</B></A><DD>
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Computes the length of the hypotenuse of a right-angled triangle
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(<I>x</I>*<I>x</I>+<I>y</I>*<I>y</I>).
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<P><DT><A NAME="M33"><B>int(</B><I>arg</I><B>)</B></A><DD>
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If <I>arg</I> is an integer value, returns <I>arg</I>, otherwise converts
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<I>arg</I> to integer by truncation and returns the converted value.
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<P><DT><A NAME="M34"><B>log(</B><I>arg</I><B>)</B></A><DD>
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Returns the natural logarithm of <I>arg</I>. <I>Arg</I> must be a
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positive value.
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<P><DT><A NAME="M35"><B>log10(</B><I>arg</I><B>)</B></A><DD>
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Returns the base 10 logarithm of <I>arg</I>. <I>Arg</I> must be a
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positive value.
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<P><DT><A NAME="M36"><B>pow(</B><I>x, y</I><B>)</B></A><DD>
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Computes the value of <I>x</I> raised to the power <I>y</I>. If <I>x</I>
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is negative, <I>y</I> must be an integer value.
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<P><DT><A NAME="M37"><B>rand()</B></A><DD>
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Returns a floating point number from zero to just less than one or,
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in mathematical terms, the range [0,1). The seed comes from the
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internal clock of the machine or may be set manual with the srand
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function.
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<P><DT><A NAME="M38"><B>round(</B><I>arg</I><B>)</B></A><DD>
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If <I>arg</I> is an integer value, returns <I>arg</I>, otherwise converts
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<I>arg</I> to integer by rounding and returns the converted value.
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<P><DT><A NAME="M39"><B>sin(</B><I>arg</I><B>)</B></A><DD>
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Returns the sine of <I>arg</I>, measured in radians.
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<P><DT><A NAME="M40"><B>sinh(</B><I>arg</I><B>)</B></A><DD>
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Returns the hyperbolic sine of <I>arg</I>. If the result would cause
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an overflow, an error is returned.
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<P><DT><A NAME="M41"><B>sqrt(</B><I>arg</I><B>)</B></A><DD>
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Returns the square root of <I>arg</I>. <I>Arg</I> must be non-negative.
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<P><DT><A NAME="M42"><B>srand(</B><I>arg</I><B>)</B></A><DD>
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The <I>arg</I>, which must be an integer, is used to reset the seed for
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the random number generator. Returns the first random number from
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that seed. Each interpreter has it's own seed.
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<P><DT><A NAME="M43"><B>tan(</B><I>arg</I><B>)</B></A><DD>
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Returns the tangent of <I>arg</I>, measured in radians.
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<P><DT><A NAME="M44"><B>tanh(</B><I>arg</I><B>)</B></A><DD>
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Returns the hyperbolic tangent of <I>arg</I>.
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<P></DL>
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<P>
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In addition to these predefined functions, applications may
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define additional functions using <B><A HREF="../TkLib/CrtMathFnc.htm">Tcl_CreateMathFunc</A></B>().
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<H3><A NAME="M45">TYPES, OVERFLOW, AND PRECISION</A></H3>
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All internal computations involving integers are done with the C type
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<I>long</I>, and all internal computations involving floating-point are
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done with the C type <I>double</I>.
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When converting a string to floating-point, exponent overflow is
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detected and results in a Tcl error.
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For conversion to integer from string, detection of overflow depends
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on the behavior of some routines in the local C library, so it should
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be regarded as unreliable.
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In any case, integer overflow and underflow are generally not detected
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reliably for intermediate results. Floating-point overflow and underflow
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are detected to the degree supported by the hardware, which is generally
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pretty reliable.
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<P>
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Conversion among internal representations for integer, floating-point,
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and string operands is done automatically as needed.
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For arithmetic computations, integers are used until some
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floating-point number is introduced, after which floating-point is used.
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For example,
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|
<PRE><B>expr 5 / 4</B></PRE>
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|
returns 1, while
|
|
<PRE><B>expr 5 / 4.0</B>
|
|
<B>expr 5 / ( [string length "abcd"] + 0.0 )</B></PRE>
|
|
both return 1.25.
|
|
Floating-point values are always returned with a ``<B>.</B>''
|
|
or an <B>e</B> so that they will not look like integer values. For
|
|
example,
|
|
<PRE><B>expr 20.0/5.0</B></PRE>
|
|
returns <B>4.0</B>, not <B>4</B>.
|
|
|
|
<H3><A NAME="M46">STRING OPERATIONS</A></H3>
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|
String values may be used as operands of the comparison operators,
|
|
although the expression evaluator tries to do comparisons as integer
|
|
or floating-point when it can.
|
|
If one of the operands of a comparison is a string and the other
|
|
has a numeric value, the numeric operand is converted back to
|
|
a string using the C <I>sprintf</I> format specifier
|
|
<B>%d</B> for integers and <B>%g</B> for floating-point values.
|
|
For example, the commands
|
|
<PRE><B>expr {"0x03" > "2"}</B>
|
|
<B>expr {"0y" < "0x12"}</B></PRE>
|
|
both return 1. The first comparison is done using integer
|
|
comparison, and the second is done using string comparison after
|
|
the second operand is converted to the string <B>18</B>.
|
|
Because of Tcl's tendency to treat values as numbers whenever
|
|
possible, it isn't generally a good idea to use operators like <B>==</B>
|
|
when you really want string comparison and the values of the
|
|
operands could be arbitrary; it's better in these cases to use
|
|
the <B><A HREF="../TkCmd/string.htm">string</A></B> command instead.
|
|
|
|
<H3><A NAME="M47">PERFORMANCE CONSIDERATIONS</A></H3>
|
|
Enclose expressions in braces for the best speed and the smallest
|
|
storage requirements.
|
|
This allows the Tcl bytecode compiler to generate the best code.
|
|
<P>
|
|
As mentioned above, expressions are substituted twice:
|
|
once by the Tcl parser and once by the <B>expr</B> command.
|
|
For example, the commands
|
|
<PRE><B>set a 3</B>
|
|
<B>set b {$a + 2}</B>
|
|
<B>expr $b*4</B></PRE>
|
|
return 11, not a multiple of 4.
|
|
This is because the Tcl parser will first substitute <B>$a + 2</B> for
|
|
the variable <B>b</B>,
|
|
then the <B>expr</B> command will evaluate the expression <B>$a + 2*4</B>.
|
|
<P>
|
|
Most expressions do not require a second round of substitutions.
|
|
Either they are enclosed in braces or, if not,
|
|
their variable and command substitutions yield numbers or strings
|
|
that don't themselves require substitutions.
|
|
However, because a few unbraced expressions
|
|
need two rounds of substitutions,
|
|
the bytecode compiler must emit
|
|
additional instructions to handle this situation.
|
|
The most expensive code is required for
|
|
unbraced expressions that contain command substitutions.
|
|
These expressions must be implemented by generating new code
|
|
each time the expression is executed.
|
|
|
|
<H3><A NAME="M48">KEYWORDS</A></H3>
|
|
<A href="../Keywords/A.htm#arithmetic">arithmetic</A>, <A href="../Keywords/B.htm#boolean">boolean</A>, <A href="../Keywords/C.htm#compare">compare</A>, <A href="../Keywords/E.htm#expression">expression</A>, <A href="../Keywords/F.htm#fuzzy comparison">fuzzy comparison</A>
|
|
<HR><PRE>
|
|
<A HREF="../copyright.htm">Copyright</A> © 1993 The Regents of the University of California.
|
|
<A HREF="../copyright.htm">Copyright</A> © 1994-2000 Sun Microsystems, Inc.
|
|
<A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE>
|
|
</BODY></HTML>
|