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C++ Mathematical Expression Toolkit Library Documentation
Section 00 - Introduction
Section 01 - Capabilities
Section 02 - Example Expressions
Section 03 - Copyright Notice
Section 04 - Downloads & Updates
Section 05 - Installation
Section 06 - Compilation
Section 07 - Compiler Compatibility
Section 08 - Built-In Operations & Functions
Section 09 - Fundamental Types
Section 10 - Components
Section 11 - Compilation Options
Section 12 - Expression Structures
Section 13 - Variable, Vector & String Definition
Section 14 - Vector Processing
Section 15 - User Defined Functions
Section 16 - Expression Dependents
Section 17 - Hierarchies Of Symbol Tables
Section 18 - Unknown Unknowns
Section 19 - Enabling & Disabling Features
Section 20 - Expression Return Values
Section 21 - Compilation Errors
Section 22 - Runtime Library Packages
Section 23 - Helpers & Utils
Section 24 - Runtime Checks
Section 25 - Benchmarking
Section 26 - Exprtk Notes
Section 27 - Simple Exprtk Example
Section 28 - Build Options
Section 29 - Files
Section 30 - Language Structure
[SECTION 00 - INTRODUCTION]
The C++ Mathematical Expression Toolkit Library (ExprTk) is a simple
to use, easy to integrate and extremely efficient run-time
mathematical expression parsing and evaluation engine. The parsing
engine supports numerous forms of functional and logic processing
semantics and is easily extensible.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 01 - CAPABILITIES]
The ExprTk expression evaluator supports the following fundamental
arithmetic operations, functions and processes:
(00) Types: Scalar, Vector, String
(01) Basic operators: +, -, *, /, %, ^
(02) Assignment: :=, +=, -=, *=, /=, %=
(03) Equalities &
Inequalities: =, ==, <>, !=, <, <=, >, >=
(04) Logic operators: and, mand, mor, nand, nor, not, or, shl, shr,
xnor, xor, true, false
(05) Functions: abs, avg, ceil, clamp, equal, erf, erfc, exp,
expm1, floor, frac, log, log10, log1p, log2,
logn, max, min, mul, ncdf, not_equal, root,
round, roundn, sgn, sqrt, sum, swap, trunc
(06) Trigonometry: acos, acosh, asin, asinh, atan, atanh, atan2,
cos, cosh, cot, csc, sec, sin, sinc, sinh,
tan, tanh, hypot, rad2deg, deg2grad, deg2rad,
grad2deg
(07) Control
structures: if-then-else, ternary conditional, switch-case,
return-statement
(08) Loop statements: while, for, repeat-until, break, continue
(09) String
processing: in, like, ilike, concatenation
(10) Optimisations: constant-folding, simple strength reduction and
dead code elimination
(11) Runtime checks: vector bounds, string bounds, loop iteration,
execution-time bounds and compilation process
checkpointing, assert statements
(12) Calculus: numerical integration and differentiation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 02 - EXAMPLE EXPRESSIONS]
The following is a short listing of infix format based mathematical
expressions that can be parsed and evaluated using the ExprTk library.
(01) sqrt(1 - (3 / x^2))
(02) clamp(-1, sin(2 * pi * x) + cos(y / 2 * pi), +1)
(03) sin(2.34e-3 * x)
(04) if(((x[2] + 2) == 3) and ((y + 5) <= 9),1 + w, 2 / z)
(05) inrange(-2,m,+2) == if(({-2 <= m} and [m <= +2]),1,0)
(06) ({1/1}*[1/2]+(1/3))-{1/4}^[1/5]+(1/6)-({1/7}+[1/8]*(1/9))
(07) a * exp(2.2 / 3.3 * t) + c
(08) z := x + sin(2.567 * pi / y)
(09) u := 2.123 * {pi * z} / (w := x + cos(y / pi))
(10) 2x + 3y + 4z + 5w == 2 * x + 3 * y + 4 * z + 5 * w
(11) 3(x + y) / 2.9 + 1.234e+12 == 3 * (x + y) / 2.9 + 1.234e+12
(12) (x + y)3.3 + 1 / 4.5 == [x + y] * 3.3 + 1 / 4.5
(13) (x + y[i])z + 1.1 / 2.7 == (x + y[i]) * z + 1.1 / 2.7
(14) (sin(x / pi) cos(2y) + 1) == (sin(x / pi) * cos(2 * y) + 1)
(15) 75x^17 + 25.1x^5 - 35x^4 - 15.2x^3 + 40x^2 - 15.3x + 1
(16) (avg(x,y) <= x + y ? x - y : x * y) + 2.345 * pi / x
(17) while (x <= 100) { x -= 1; }
(18) x <= 'abc123' and (y in 'AString') or ('1x2y3z' != z)
(19) ((x + 'abc') like '*123*') or ('a123b' ilike y)
(20) sgn(+1.2^3.4z / -5.6y) <= {-7.8^9 / -10.11x }
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 03 - COPYRIGHT NOTICE]
Free use of the C++ Mathematical Expression Toolkit Library is
permitted under the guidelines and in accordance with the most current
version of the MIT License.
(1) https://www.opensource.org/licenses/MIT
(2) SPDX-License-Identifier: MIT
(3) SPDX-FileCopyrightText : Copyright (C) 1999-2024 Arash Partow
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 04 - DOWNLOADS & UPDATES]
The most recent version of the C++ Mathematical Expression Toolkit
Library including all updates and tests can be found at the following
locations:
(1) Download: https://www.partow.net/programming/exprtk/index.html
(2) Mirror Repository: https://github.com/ArashPartow/exprtk
https://github.com/ArashPartow/exprtk-extras
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 05 - INSTALLATION]
The header file exprtk.hpp should be placed in a project or system
include path (e.g: /usr/include/).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 06 - COMPILATION]
The ExprTk package contains the ExprTk header, a set of simple
examples and a benchmark and unit test suite. The following is a list
of commands to build the various components:
(a) For a complete build: make clean all
(b) For a PGO build: make clean pgo
(c) To strip executables: make strip_bin
(d) Execute valgrind check: make valgrind_check
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 07 - COMPILER COMPATIBILITY]
ExprTk has been built error and warning free using the following set
of C++ compilers:
(*) GNU Compiler Collection (3.5+)
(*) Clang/LLVM (1.1+)
(*) Microsoft Visual Studio C++ Compiler (7.1+)
(*) Intel C++ Compiler (8.x+)
(*) AMD Optimizing C++ Compiler (1.2+)
(*) Nvidia C++ Compiler (19.x+)
(*) PGI C++ (10.x+)
(*) Circle C++ (circa: b81c37d2bb227c)
(*) IBM XL C/C++ (9.x+)
(*) C++ Builder (XE4+)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 08 - BUILT-IN OPERATIONS & FUNCTIONS]
(0) Arithmetic & Assignment Operators
+----------+---------------------------------------------------------+
| OPERATOR | DEFINITION |
+----------+---------------------------------------------------------+
| + | Addition between x and y. (eg: x + y) |
+----------+---------------------------------------------------------+
| - | Subtraction between x and y. (eg: x - y) |
+----------+---------------------------------------------------------+
| * | Multiplication between x and y. (eg: x * y) |
+----------+---------------------------------------------------------+
| / | Division between x and y. (eg: x / y) |
+----------+---------------------------------------------------------+
| % | Modulus of x with respect to y. (eg: x % y) |
+----------+---------------------------------------------------------+
| ^ | x to the power of y. (eg: x ^ y) |
+----------+---------------------------------------------------------+
| := | Assign the value of x to y. Where y is either a variable|
| | or vector type. (eg: y := x) |
+----------+---------------------------------------------------------+
| += | Increment x by the value of the expression on the right |
| | hand side. Where x is either a variable or vector type. |
| | (eg: x += abs(y - z)) |
+----------+---------------------------------------------------------+
| -= | Decrement x by the value of the expression on the right |
| | hand side. Where x is either a variable or vector type. |
| | (eg: x[i] -= abs(y + z)) |
+----------+---------------------------------------------------------+
| *= | Assign the multiplication of x by the value of the |
| | expression on the righthand side to x. Where x is either|
| | a variable or vector type. |
| | (eg: x *= abs(y / z)) |
+----------+---------------------------------------------------------+
| /= | Assign the division of x by the value of the expression |
| | on the right-hand side to x. Where x is either a |
| | variable or vector type. (eg: x[i + j] /= abs(y * z)) |
+----------+---------------------------------------------------------+
| %= | Assign x modulo the value of the expression on the right|
| | hand side to x. Where x is either a variable or vector |
| | type. (eg: x[2] %= y ^ 2) |
+----------+---------------------------------------------------------+
(1) Equalities & Inequalities
+----------+---------------------------------------------------------+
| OPERATOR | DEFINITION |
+----------+---------------------------------------------------------+
| == or = | True only if x is strictly equal to y. (eg: x == y) |
+----------+---------------------------------------------------------+
| <> or != | True only if x does not equal y. (eg: x <> y or x != y) |
+----------+---------------------------------------------------------+
| < | True only if x is less than y. (eg: x < y) |
+----------+---------------------------------------------------------+
| <= | True only if x is less than or equal to y. (eg: x <= y) |
+----------+---------------------------------------------------------+
| > | True only if x is greater than y. (eg: x > y) |
+----------+---------------------------------------------------------+
| >= | True only if x greater than or equal to y. (eg: x >= y) |
+----------+---------------------------------------------------------+
(2) Boolean Operations
+----------+---------------------------------------------------------+
| OPERATOR | DEFINITION |
+----------+---------------------------------------------------------+
| true | True state or any value other than zero (typically 1). |
+----------+---------------------------------------------------------+
| false | False state, value of exactly zero. |
+----------+---------------------------------------------------------+
| and | Logical AND, True only if x and y are both true. |
| | (eg: x and y) |
+----------+---------------------------------------------------------+
| mand | Multi-input logical AND, True only if all inputs are |
| | true. Left to right short-circuiting of expressions. |
| | (eg: mand(x > y, z < w, u or v, w and x)) |
+----------+---------------------------------------------------------+
| mor | Multi-input logical OR, True if at least one of the |
| | inputs are true. Left to right short-circuiting of |
| | expressions. (eg: mor(x > y, z < w, u or v, w and x)) |
+----------+---------------------------------------------------------+
| nand | Logical NAND, True only if either x or y is false. |
| | (eg: x nand y) |
+----------+---------------------------------------------------------+
| nor | Logical NOR, True only if the result of x or y is false |
| | (eg: x nor y) |
+----------+---------------------------------------------------------+
| not | Logical NOT, Negate the logical sense of the input. |
| | (eg: not(x and y) == x nand y) |
+----------+---------------------------------------------------------+
| or | Logical OR, True if either x or y is true. (eg: x or y) |
+----------+---------------------------------------------------------+
| xor | Logical XOR, True only if the logical states of x and y |
| | differ. (eg: x xor y) |
+----------+---------------------------------------------------------+
| xnor | Logical XNOR, True iff the biconditional of x and y is |
| | satisfied. (eg: x xnor y) |
+----------+---------------------------------------------------------+
| & | Similar to AND but with left to right expression short |
| | circuiting optimisation. (eg: (x & y) == (y and x)) |
+----------+---------------------------------------------------------+
| | | Similar to OR but with left to right expression short |
| | circuiting optimisation. (eg: (x | y) == (y or x)) |
+----------+---------------------------------------------------------+
(3) General Purpose Functions
+----------+---------------------------------------------------------+
| FUNCTION | DEFINITION |
+----------+---------------------------------------------------------+
| abs | Absolute value of x. (eg: abs(x)) |
+----------+---------------------------------------------------------+
| avg | Average of all the inputs. |
| | (eg: avg(x,y,z,w,u,v) == (x + y + z + w + u + v) / 6) |
+----------+---------------------------------------------------------+
| ceil | Smallest integer that is greater than or equal to x. |
+----------+---------------------------------------------------------+
| clamp | Clamp x in range between r0 and r1, where r0 < r1. |
| | (eg: clamp(r0,x,r1)) |
+----------+---------------------------------------------------------+
| equal | Equality test between x and y using normalised epsilon |
+----------+---------------------------------------------------------+
| erf | Error function of x. (eg: erf(x)) |
+----------+---------------------------------------------------------+
| erfc | Complimentary error function of x. (eg: erfc(x)) |
+----------+---------------------------------------------------------+
| exp | e to the power of x. (eg: exp(x)) |
+----------+---------------------------------------------------------+
| expm1 | e to the power of x minus 1, where x is very small. |
| | (eg: expm1(x)) |
+----------+---------------------------------------------------------+
| floor | Largest integer that is less than or equal to x. |
| | (eg: floor(x)) |
+----------+---------------------------------------------------------+
| frac | Fractional portion of x. (eg: frac(x)) |
+----------+---------------------------------------------------------+
| hypot | Hypotenuse of x and y (eg: hypot(x,y) = sqrt(x*x + y*y))|
+----------+---------------------------------------------------------+
| iclamp | Inverse-clamp x outside of the range r0 and r1. Where |
| | r0 < r1. If x is within the range it will snap to the |
| | closest bound. (eg: iclamp(r0,x,r1) |
+----------+---------------------------------------------------------+
| inrange | In-range returns 'true' when x is within the range r0 |
| | and r1. Where r0 < r1. (eg: inrange(r0,x,r1) |
+----------+---------------------------------------------------------+
| log | Natural logarithm of x. (eg: log(x)) |
+----------+---------------------------------------------------------+
| log10 | Base 10 logarithm of x. (eg: log10(x)) |
+----------+---------------------------------------------------------+
| log1p | Natural logarithm of 1 + x, where x is very small. |
| | (eg: log1p(x)) |
+----------+---------------------------------------------------------+
| log2 | Base 2 logarithm of x. (eg: log2(x)) |
+----------+---------------------------------------------------------+
| logn | Base N logarithm of x. where n is a positive integer. |
| | (eg: logn(x,8)) |
+----------+---------------------------------------------------------+
| max | Largest value of all the inputs. (eg: max(x,y,z,w,u,v)) |
+----------+---------------------------------------------------------+
| min | Smallest value of all the inputs. (eg: min(x,y,z,w,u)) |
+----------+---------------------------------------------------------+
| mul | Product of all the inputs. |
| | (eg: mul(x,y,z,w,u,v,t) == (x * y * z * w * u * v * t)) |
+----------+---------------------------------------------------------+
| ncdf | Normal cumulative distribution function. (eg: ncdf(x)) |
+----------+---------------------------------------------------------+
| not_equal| Not-equal test between x and y using normalised epsilon |
+----------+---------------------------------------------------------+
| pow | x to the power of y. (eg: pow(x,y) == x ^ y) |
+----------+---------------------------------------------------------+
| root | Nth-Root of x. where n is a positive integer. |
| | (eg: root(x,3) == x^(1/3)) |
+----------+---------------------------------------------------------+
| round | Round x to the nearest integer. (eg: round(x)) |
+----------+---------------------------------------------------------+
| roundn | Round x to n decimal places (eg: roundn(x,3)) |
| | where n > 0 and is an integer. |
| | (eg: roundn(1.2345678,4) == 1.2346) |
+----------+---------------------------------------------------------+
| sgn | Sign of x, -1 where x < 0, +1 where x > 0, else zero. |
| | (eg: sgn(x)) |
+----------+---------------------------------------------------------+
| sqrt | Square root of x, where x >= 0. (eg: sqrt(x)) |
+----------+---------------------------------------------------------+
| sum | Sum of all the inputs. |
| | (eg: sum(x,y,z,w,u,v,t) == (x + y + z + w + u + v + t)) |
+----------+---------------------------------------------------------+
| swap | Swap the values of the variables x and y and return the |
| <=> | current value of y. (eg: swap(x,y) or x <=> y) |
+----------+---------------------------------------------------------+
| trunc | Integer portion of x. (eg: trunc(x)) |
+----------+---------------------------------------------------------+
(4) Trigonometry Functions
+----------+---------------------------------------------------------+
| FUNCTION | DEFINITION |
+----------+---------------------------------------------------------+
| acos | Arc cosine of x expressed in radians. Interval [-1,+1] |
| | (eg: acos(x)) |
+----------+---------------------------------------------------------+
| acosh | Inverse hyperbolic cosine of x expressed in radians. |
| | (eg: acosh(x)) |
+----------+---------------------------------------------------------+
| asin | Arc sine of x expressed in radians. Interval [-1,+1] |
| | (eg: asin(x)) |
+----------+---------------------------------------------------------+
| asinh | Inverse hyperbolic sine of x expressed in radians. |
| | (eg: asinh(x)) |
+----------+---------------------------------------------------------+
| atan | Arc tangent of x expressed in radians. Interval [-1,+1] |
| | (eg: atan(x)) |
+----------+---------------------------------------------------------+
| atan2 | Arc tangent of (x / y) expressed in radians. [-pi,+pi] |
| | eg: atan2(x,y) |
+----------+---------------------------------------------------------+
| atanh | Inverse hyperbolic tangent of x expressed in radians. |
| | (eg: atanh(x)) |
+----------+---------------------------------------------------------+
| cos | Cosine of x. (eg: cos(x)) |
+----------+---------------------------------------------------------+
| cosh | Hyperbolic cosine of x. (eg: cosh(x)) |
+----------+---------------------------------------------------------+
| cot | Cotangent of x. (eg: cot(x)) |
+----------+---------------------------------------------------------+
| csc | Cosecant of x. (eg: csc(x)) |
+----------+---------------------------------------------------------+
| sec | Secant of x. (eg: sec(x)) |
+----------+---------------------------------------------------------+
| sin | Sine of x. (eg: sin(x)) |
+----------+---------------------------------------------------------+
| sinc | Sine cardinal of x. (eg: sinc(x)) |
+----------+---------------------------------------------------------+
| sinh | Hyperbolic sine of x. (eg: sinh(x)) |
+----------+---------------------------------------------------------+
| tan | Tangent of x. (eg: tan(x)) |
+----------+---------------------------------------------------------+
| tanh | Hyperbolic tangent of x. (eg: tanh(x)) |
+----------+---------------------------------------------------------+
| deg2rad | Convert x from degrees to radians. (eg: deg2rad(x)) |
+----------+---------------------------------------------------------+
| deg2grad | Convert x from degrees to gradians. (eg: deg2grad(x)) |
+----------+---------------------------------------------------------+
| rad2deg | Convert x from radians to degrees. (eg: rad2deg(x)) |
+----------+---------------------------------------------------------+
| grad2deg | Convert x from gradians to degrees. (eg: grad2deg(x)) |
+----------+---------------------------------------------------------+
(5) String Processing
+----------+---------------------------------------------------------+
| FUNCTION | DEFINITION |
+----------+---------------------------------------------------------+
| = , == | All common equality/inequality operators are applicable |
| !=, <> | to strings and are applied in a case sensitive manner. |
| <=, >= | In the following example x, y and z are of type string. |
| < , > | (eg: not((x <= 'AbC') and ('1x2y3z' <> y)) or (z == x) |
+----------+---------------------------------------------------------+
| in | True only if x is a substring of y. |
| | (eg: x in y or 'abc' in 'abcdefgh') |
+----------+---------------------------------------------------------+
| like | True only if the string x matches the pattern y. |
| | Available wildcard characters are '*' and '?' denoting |
| | zero or more and zero or one matches respectively. |
| | (eg: x like y or 'abcdefgh' like 'a?d*h') |
+----------+---------------------------------------------------------+
| ilike | True only if the string x matches the pattern y in a |
| | case insensitive manner. Available wildcard characters |
| | are '*' and '?' denoting zero or more and zero or one |
| | matches respectively. |
| | (eg: x ilike y or 'a1B2c3D4e5F6g7H' ilike 'a?d*h') |
+----------+---------------------------------------------------------+
| [r0:r1] | The closed interval[r0,r1] of the specified string. |
| | eg: Given a string x with a value of 'abcdefgh' then: |
| | 1. x[1:4] == 'bcde' |
| | 2. x[ :4] == x[:8 / 2] == 'abcde' |
| | 3. x[2 + 1: ] == x[3:] =='defgh' |
| | 4. x[ : ] == x[:] == 'abcdefgh' |
| | 5. x[4/2:3+1] == x[2:4] == 'cde' |
| | |
| | Note: Both r0 and r1 are assumed to be integers, where |
| | r0 <= r1. They may also be the result of an expression, |
| | in the event they have fractional components truncation |
| | shall be performed. (eg: 1.67 --> 1) |
+----------+---------------------------------------------------------+
| := | Assign the value of x to y. Where y is a mutable string |
| | or string range and x is either a string or a string |
| | range. eg: |
| | 1. y := x |
| | 2. y := 'abc' |
| | 3. y := x[:i + j] |
| | 4. y := '0123456789'[2:7] |
| | 5. y := '0123456789'[2i + 1:7] |
| | 6. y := (x := '0123456789'[2:7]) |
| | 7. y[i:j] := x |
| | 8. y[i:j] := (x + 'abcdefg'[8 / 4:5])[m:n] |
| | |
| | Note: For options 7 and 8 the shorter of the two ranges |
| | will denote the number characters that are to be copied.|
+----------+---------------------------------------------------------+
| + | Concatenation of x and y. Where x and y are strings or |
| | string ranges. eg |
| | 1. x + y |
| | 2. x + 'abc' |
| | 3. x + y[:i + j] |
| | 4. x[i:j] + y[2:3] + '0123456789'[2:7] |
| | 5. 'abc' + x + y |
| | 6. 'abc' + '1234567' |
| | 7. (x + 'a1B2c3D4' + y)[i:2j] |
+----------+---------------------------------------------------------+
| += | Append to x the value of y. Where x is a mutable string |
| | and y is either a string or a string range. eg: |
| | 1. x += y |
| | 2. x += 'abc' |
| | 3. x += y[:i + j] + 'abc' |
| | 4. x += '0123456789'[2:7] |
+----------+---------------------------------------------------------+
| <=> | Swap the values of x and y. Where x and y are mutable |
| | strings. (eg: x <=> y) |
+----------+---------------------------------------------------------+
| [] | The string size operator returns the size of the string |
| | being actioned. |
| | eg: |
| | 1. 'abc'[] == 3 |
| | 2. var max_str_length := max(s0[], s1[], s2[], s3[]) |
| | 3. ('abc' + 'd')[] == 6 |
| | 4. (('abc' + 'xyz')[1:4])[] == 4 |
+----------+---------------------------------------------------------+
(6) Control Structures
+----------+---------------------------------------------------------+
|STRUCTURE | DEFINITION |
+----------+---------------------------------------------------------+
| if | If x is true then return y else return z. |
| | eg: |
| | 1. if (x, y, z) |
| | 2. if ((x + 1) > 2y, z + 1, w / v) |
| | 3. if (x > y) z; |
| | 4. if (x <= 2*y) { z + w }; |
+----------+---------------------------------------------------------+
| if-else | The if-else/else-if statement. Subject to the condition |
| | branch the statement will return either the value of the|
| | consequent or the alternative branch. |
| | eg: |
| | 1. if (x > y) z; else w; |
| | 2. if (x > y) z; else if (w != u) v; |
| | 3. if (x < y) { z; w + 1; } else u; |
| | 4. if ((x != y) and (z > w)) |
| | { |
| | y := sin(x) / u; |
| | z := w + 1; |
| | } |
| | else if (x > (z + 1)) |
| | { |
| | w := abs (x - y) + z; |
| | u := (x + 1) > 2y ? 2u : 3u; |
| | } |
+----------+---------------------------------------------------------+
| switch | The first true case condition that is encountered will |
| | determine the result of the switch. If none of the case |
| | conditions hold true, the default action is assumed as |
| | the final return value. This is sometimes also known as |
| | a multi-way branch mechanism. |
| | eg: |
| | switch |
| | { |
| | case x > (y + z) : 2 * x / abs(y - z); |
| | case x < 3 : sin(x + y); |
| | default : 1 + x; |
| | } |
+----------+---------------------------------------------------------+
| while | The structure will repeatedly evaluate the internal |
| | statement(s) 'while' the condition is true. The final |
| | statement in the final iteration shall be used as the |
| | return value of the loop. |
| | eg: |
| | while ((x -= 1) > 0) |
| | { |
| | y := x + z; |
| | w := u + y; |
| | } |
+----------+---------------------------------------------------------+
| repeat/ | The structure will repeatedly evaluate the internal |
| until | statement(s) 'until' the condition is true. The final |
| | statement in the final iteration shall be used as the |
| | return value of the loop. |
| | eg: |
| | repeat |
| | y := x + z; |
| | w := u + y; |
| | until ((x += 1) > 100) |
+----------+---------------------------------------------------------+
| for | The structure will repeatedly evaluate the internal |
| | statement(s) while the condition is true. On each loop |
| | iteration, an 'incrementing' expression is evaluated. |
| | The conditional is mandatory whereas the initialiser |
| | and incrementing expressions are optional. |
| | eg: |
| | for (var x := 0; (x < n) and (x != y); x += 1) |
| | { |
| | y := y + x / 2 - z; |
| | w := u + y; |
| | } |
+----------+---------------------------------------------------------+
| break | Break terminates the execution of the nearest enclosed |
| break[] | loop, allowing for the execution to continue on external|
| | to the loop. The default break statement will set the |
| | return value of the loop to NaN, where as the return |
| | based form will set the value to that of the break |
| | expression. |
| | eg: |
| | while ((i += 1) < 10) |
| | { |
| | if (i < 5) |
| | j -= i + 2; |
| | else if (i % 2 == 0) |
| | break; |
| | else |
| | break[2i + 3]; |
| | } |
+----------+---------------------------------------------------------+
| continue | Continue results in the remaining portion of the nearest|
| | enclosing loop body to be skipped. |
| | eg: |
| | for (var i := 0; i < 10; i += 1) |
| | { |
| | if (i < 5) |
| | continue; |
| | j -= i + 2; |
| | } |
+----------+---------------------------------------------------------+
| return | Return immediately from within the current expression. |
| | With the option of passing back a variable number of |
| | values (scalar, vector or string). eg: |
| | 1. return [1]; |
| | 2. return [x, 'abx']; |
| | 3. return [x, x + y,'abx']; |
| | 4. return []; |
| | 5. if (x < y) |
| | return [x, x - y, 'result-set1', 123.456]; |
| | else |
| | return [y, x + y, 'result-set2']; |
+----------+---------------------------------------------------------+
| ?: | Ternary conditional statement, similar to that of the |
| | above denoted if-statement. |
| | eg: |
| | 1. x ? y : z |
| | 2. x + 1 > 2y ? z + 1 : (w / v) |
| | 3. min(x,y) > z ? (x < y + 1) ? x : y : (w * v) |
+----------+---------------------------------------------------------+
| ~ | Evaluate each sub-expression, then return as the result |
| | the value of the last sub-expression. This is sometimes |
| | known as multiple sequence point evaluation. |
| | eg: |
| | ~(i := x + 1, j := y / z, k := sin(w/u)) == (sin(w/u))) |
| | ~{i := x + 1; j := y / z; k := sin(w/u)} == (sin(w/u))) |
+----------+---------------------------------------------------------+
| [*] | Evaluate any consequent for which its case statement is |
| | true. The return value will be either zero or the result|
| | of the last consequent to have been evaluated. |
| | eg: |
| | [*] |
| | { |
| | case (x + 1) > (y - 2) : x := z / 2 + sin(y / pi); |
| | case (x + 2) < abs(y + 3) : w / 4 + min(5y,9); |
| | case (x + 3) == (y * 4) : y := abs(z / 6) + 7y; |
| | } |
+----------+---------------------------------------------------------+
| [] | The vector size operator returns the size of the vector |
| | being actioned. |
| | eg: |
| | 1. v[] |
| | 2. max_size := max(v0[],v1[],v2[],v3[]) |
+----------+---------------------------------------------------------+
Note01: In the tables above, the symbols x, y, z, w, u and v where
appropriate may represent any of one the following:
1. Literal numeric/string value
2. A variable
3. A vector element
4. A vector
5. A string
6. An expression comprised of [1], [2] or [3] (eg: 2 + x / vec[3])
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 09 - FUNDAMENTAL TYPES]
ExprTk supports three fundamental types which can be used freely in
expressions. The types are as follows:
(1) Scalar
(2) Vector
(3) String
(1) Scalar Type
The scalar type is a singular numeric value. The underlying type is
that used to specialise the ExprTk components (float, double, long
double, MPFR et al).
(2) Vector Type
The vector type is a fixed size sequence of contiguous scalar values.
A vector can be indexed resulting in a scalar value. Operations
between a vector and scalar will result in a vector with a size equal
to that of the original vector, whereas operations between vectors
will result in a vector of size equal to that of the smaller of the
two. In both mentioned cases, the operations will occur element-wise.
(3) String Type
The string type is a variable length sequence of 8-bit chars. Strings
can be assigned and concatenated to one another, they can also be
manipulated via sub-ranges using the range definition syntax. Strings
however can not interact with scalar or vector types.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 10 - COMPONENTS]
There are three primary components, that are specialised upon a given
numeric type, which make up the core of ExprTk. The components are as
follows:
(1) Symbol Table exprtk::symbol_table<NumericType>
(2) Expression exprtk::expression<NumericType>
(3) Parser exprtk::parser<NumericType>
(1) Symbol Table
A structure that is used to store references to variables, constants
and functions that are to be used within expressions. Furthermore in
the context of composited recursive functions the symbol table can
also be thought of as a simple representation of a stack specific for
the expression(s) that reference it. The following is a list of the
types a symbol table can handle:
(a) Numeric variables
(b) Numeric constants
(c) Numeric vector elements
(d) String variables
(e) String constants
(f) Functions
(g) Vararg functions
During the compilation process if an expression is found to require
any of the elements noted above, the expression's associated
symbol_table will be queried for the element and if present a
reference to the element will be embedded within the expression's AST.
This allows for the original element to be modified independently of
the expression instance and to also allow the expression to be
evaluated using the current value of the element.
The example below demonstrates the relationship between variables,
symbol_table and expression. Note the variables are modified as they
normally would in a program, and when the expression is evaluated the
current values assigned to the variables shall be used.
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
double x = 0;
double y = 0;
symbol_table_t symbol_table;
expression_t expression;
parser_t parser;
std::string expression_string = "x * y + 3";
symbol_table.add_variable("x",x);
symbol_table.add_variable("y",y);
expression.register_symbol_table(symbol_table);
parser.compile(expression_string,expression);
x = 1.0;
y = 2.0;
expression.value(); // 1 * 2 + 3
x = 3.7;
expression.value(); // 3.7 * 2 + 3
y = -9.0;
expression.value(); // 3.7 * -9 + 3
// 'x * -9 + 3' for x in range of [0,100) in steps of 0.0001
for (x = 0.0; x < 100.0; x += 0.0001)
{
expression.value(); // x * -9 + 3
}
Note02: Any variable reference provided to a given symbol_table
instance, must have a lifetime at least as long as the lifetime of the
symbol_table instance. In the event the variable reference is
invalidated before the symbol_table or any dependent expression
instances have been destructed, then any associated expression
evaluations or variable referencing via the symbol_table instance will
result in undefined behaviour.
The following bit of code instantiates a symbol_table and expression
instance, then proceeds to demonstrate various ways in which
references to variables can be added to the symbol_table, and how
those references are subsequently invalidated resulting in various
forms of undefined behaviour.
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
symbol_table_t symbol_table;
expression_t expression;
std::deque<double > y {1.1, 2.2, 3.3};
std::vector<double> z {4.4, 5.5, 6.6};
double* w = new double(123.456);
{
double x = 123.4567;
symbol_table.add_variable("x", x);
} // Reference to variable x has been invalidated
symbol_table.add_variable("y", y.back());
y.pop_back(); // Reference to variable y has been invalidated
symbol_table.add_variable("z", z.front());
z.erase(z.begin());
// Reference to variable z has been invalidated
symbol_table.add_variable("w", *w);
delete w; // Reference to variable w has been invalidated
const std::string expression_string = "x + y / z * w";
// Compilation of expression will succeed
parser.compile(expression_string,expression);
expression.value();
// Evaluation will result in undefined behaviour
// due to 'x' and 'w' having been destroyed.
symbol_table.get_variable("x")->ref() = 135.791;
// Assignment will result in undefined behaviour
A compiled expression that references variables from a symbol_table is
dependent on that symbol_table instance and the variables it holds
being valid.
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
symbol_table_t symbol_table;
expression_t expression;
double x = 123.456;
symbol_table.add_variable("x", x);
const std::string expression_string = "(x + 1) / 2";
// Compilation of the expression will succeed
parser.compile(expression_string,expression);
// Clear all variables from symbol_table
symbol_table.clear();
expression.value();
// Evaluation will result in undefined behaviour
// because the reference to 'x' having been destroyed
// during the clearing of the symbol_table
In the above example, an expression is compiled that references
variable "x". As part of the compilation process the node holding the
variable "x" is obtained from the symbol_table and embedded in the AST
of the expression - in short the expression is now referencing the
node that holds the variable "x". The following diagram depicts the
dependencies between the variable x, the symbol table and the
expression:
+--[Symbol Table]--+
| |
| +- ------+ |
| | x-node | |
| +-----A--+ | +--[Expression]--+
+---|---|----------+ | +---------+ |
v | | | A.S.T | |
| +--------<--------[.] | |
+-----+ | +---------+ |
| +----------------+
+-v-[variable]---+
| x: 123.456 |
+----------------+
When the clear method is called on the symbol table the X-Node is
destroyed, so now the expression is referencing a node that has been
destroyed. From this point onwards any attempts to reference the
expression instance will result in undefined behaviour. Simply put the
above example violates the requirement that the lifetime of any
objects referenced by expressions should exceed the lifetime of the
expression instance.
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
symbol_table_t symbol_table;
expression_t expression;
double x = 123.456;
symbol_table.add_variable("x", x);
const std::string expression_string = "(x + 1) / 2";
// Compilation of the expression will succeed
parser.compile(expression_string,expression);
expression.value();
// Release the expression and its dependents
expression.release();
// Clear all variables from symbol_table
symbol_table.clear();
expression.value();
// Will return null_node value of NaN
In the above example the expression is released before the associated
symbol_table is cleared of its variables, which resolves the undefined
behaviour issue noted in the previous example.
Note03: It is possible to register multiple symbol_tables with a
single expression object. In the event an expression has multiple
symbol tables, and where there exists conflicts between symbols, the
compilation stage will resolve the conflicts based on the order of
registration of the symbol_tables to the expression. For a more
expansive discussion please review section [17 - Hierarchies Of Symbol
Tables]
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
symbol_table_t symbol_table0;
symbol_table_t symbol_table1;
expression_t expression;
parser_t parser;
double x0 = 123.0;
double x1 = 678.0;
std::string expression_string = "x + 1";
symbol_table0.add_variable("x",x0);
symbol_table1.add_variable("x",x1);
expression.register_symbol_table(symbol_table0);
expression.register_symbol_table(symbol_table1);
parser.compile(expression_string,expression);
expression.value(); // 123 + 1
The symbol table supports adding references to external instances of
types that can be accessed within expressions via the following
methods:
1. bool add_variable (const std::string& name, scalar_t& )
2. bool add_constant (const std::string& name, const scalar_t& )
3. bool add_stringvar (const std::string& name, std::string& )
4. bool add_vector (const std::string& name, vector_type& )
5. bool add_function (const std::string& name, function_t& )
6. bool create_stringvar(const std::string& name,const std::string&)
7. bool create_variable (const std::string& name, const T& )
Note04: The 'vector' type must be comprised from a contiguous array of
scalars with a size that is larger than zero. The vector type itself
can be any one of the following:
1. std::vector<scalar_t>
2. scalar_t(&v)[N]
3. scalar_t* and array size
4. exprtk::vector_view<scalar_t>
When registering a variable, vector, string or function with an
instance of a symbol_table, the call to 'add_...' may fail and return
a false result due to one or more of the following reasons:
1. Variable name contains invalid characters or is ill-formed
2. Variable name conflicts with a reserved word (eg: 'while')
3. Variable name conflicts with a previously registered variable
4. A vector of size (length) zero is being registered
5. A free function exceeding fifteen parameters is being registered
6. The symbol_table instance is in an invalid state
Note05: The symbol_table has a method called clear, which when invoked
will clear all variables, vectors, strings and functions registered
with the symbol_table instance. If this method is to be called, then
one must make sure that all compiled expression instances that
reference variables belonging to that symbol_table instance are
released (aka call release method on expression) before calling the
clear method on the symbol_table instance, otherwise undefined
behaviours will occur.
A further property of symbol tables is that they can be classified at
instantiation as either being mutable (by default) or immutable. This
property determines if variables, vectors or strings registered with
the symbol table can undergo modifications within expressions that
reference them. The following demonstrates construction of an
immutable symbol table instance:
symbol_table_t immutable_symbol_table
(symbol_table_t::symtab_mutability_type::e_immutable);