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| -rw-r--r-- | doc/expr.n | 58 |
1 files changed, 49 insertions, 9 deletions
@@ -5,7 +5,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: expr.n,v 1.12 2003/09/12 23:55:32 dkf Exp $ +'\" RCS: @(#) $Id: expr.n,v 1.13 2004/05/24 12:47:56 dkf Exp $ '\" .so man.macros .TH expr n 8.5 Tcl "Tcl Built-In Commands" @@ -34,7 +34,7 @@ evaluates to 14.2. Tcl expressions differ from C expressions in the way that operands are specified. Also, Tcl expressions support non-numeric operands and string comparisons. -.SH OPERANDS +.SS OPERANDS .PP A Tcl expression consists of a combination of operands, operators, and parentheses. @@ -105,7 +105,7 @@ expr 2 + "$a.$b" 5.6 expr 4*[llength "6 2"] 8 expr {{word one} < "word $a"} 0\fR .CE -.SH OPERATORS +.SS OPERATORS .PP The valid operators are listed below, grouped in decreasing order of precedence: @@ -199,7 +199,7 @@ depending on the value of \fB$v\fR. Note, however, that this is only true if the entire expression is enclosed in braces; otherwise the Tcl parser will evaluate both \fB[a]\fR and \fB[b]\fR before invoking the \fBexpr\fR command. -.SH "MATH FUNCTIONS" +.SS "MATH FUNCTIONS" .PP Tcl supports the following mathematical functions in expressions, all of which work solely with floating-point numbers unless otherwise noted: @@ -326,7 +326,7 @@ if \fIarg\fR is a 32-bit number) if it is not one already. .PP In addition to these predefined functions, applications may define additional functions using \fBTcl_CreateMathFunc\fR(). -.SH "TYPES, OVERFLOW, AND PRECISION" +.SS "TYPES, OVERFLOW, AND PRECISION" .PP All internal computations involving integers are done with the C type \fIlong\fR, and all internal computations involving floating-point are @@ -362,8 +362,7 @@ example, \fBexpr 20.0/5.0\fR .CE returns \fB4.0\fR, not \fB4\fR. - -.SH "STRING OPERATIONS" +.SS "STRING OPERATIONS" .PP String values may be used as operands of the comparison operators, although the expression evaluator tries to do comparisons as integer @@ -386,7 +385,6 @@ possible, it isn't generally a good idea to use operators like \fB==\fR when you really want string comparison and the values of the operands could be arbitrary; it's better in these cases to use the \fBeq\fR or \fBne\fR operators, or the \fBstring\fR command instead. - .SH "PERFORMANCE CONSIDERATIONS" .PP Enclose expressions in braces for the best speed and the smallest @@ -418,9 +416,51 @@ 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. +.SH EXAMPLES +Define a procedure that computes an "interesting" mathematical +function: +.CS +proc calc {x y} { + expr { ($x**2 - $y**2) / exp($x**2 + $y**2) } +} +.CE + +Convert polar coordinates into cartesian coordinates: +.CS +# convert from ($radius,$angle) +set x [expr { $radius * cos($angle) }] +set y [expr { $radius * sin($angle) }] +.CE + +Convert cartesian coordinates into polar coordinates: +.CS +# convert from ($x,$y) +set radius [expr { hypot($y, $x) }] +set angle [expr { atan2($y, $x) }] +.CE + +Print a message describing the relationship of two string values to +each other: +.CS +puts "a and b are [expr {$a eq $b ? {equal} : {different}}]" +.CE + +Set a variable to whether an environment variable is both defined at +all and also set to a true boolean value: +.CS +set isTrue [expr { + [info exists ::env(SOME_ENV_VAR)] && + [string is true -strict $::env(SOME_ENV_VAR)] +}] +.CE + +Generate a random integer in the range 0..99 inclusive: +.CS +set randNum [expr { int(100 * rand()) }] +.CE .SH "SEE ALSO" -array(n), string(n), Tcl(n) +array(n), for(n), if(n), string(n), Tcl(n), while(n) .SH KEYWORDS arithmetic, boolean, compare, expression, fuzzy comparison |