如何评估在PHP中作为字符串传递的公式？

这可能会有所帮助。

http://www.phpclasses.org/browse/package/2695.html

需要下载恼人的登录名。我为您复制了粘贴内容。

• 此类可用于安全地评估数学表达式。
• 该类可以采用文本字符串中的表达式，然后通过替换变量的值并计算数学函数和运算的结果来对其进行求值。
• 它支持隐式乘法，多变量函数和嵌套函数。
• 它可用于评估来自不受信任来源的表达式。 它提供了强大的错误检查功能，并且仅评估一组有限的功能。
• 它可用于根据公式表达式生成图。

  class evalMath {    var $suppress_errors = false;    var $last_error = null;    var $v = array('e'=>2.71,'pi'=>3.14); // variables (and constants)    var $f = array(); // user-defined functions    var $vb = array('e', 'pi'); // constants    var $fb = array(  // built-in functions        'sin','sinh','arcsin','asin','arcsinh','asinh',        'cos','cosh','arccos','acos','arccosh','acosh',        'tan','tanh','arctan','atan','arctanh','atanh',        'sqrt','abs','ln','log');    function evalMath() {        // make the variables a little more accurate        $this->v['pi'] = pi();        $this->v['e'] = exp(1);    }    function e($expr) {        return $this->evaluate($expr);    }    function evaluate($expr) {        $this->last_error = null;        $expr = trim($expr);        if (substr($expr, -1, 1) == ';') $expr = substr($expr, 0, strlen($expr)-1); // strip semicolons at the end        //===============        // is it a variable assignment?        if (preg_match('/^s*([a-z]w*)s*=s*(.+)$/', $expr, $matches)) { if (in_array($matches[1], $this->vb)) { // make sure we're not assigning to a constant     return $this->trigger("cannot assign to constant '$matches[1]'"); } if (($tmp = $this->pfx($this->nfx($matches[2]))) === false) return false; // get the result and make sure it's good $this->v[$matches[1]] = $tmp; // if so, stick it in the variable array return $this->v[$matches[1]]; // and return the resulting value        //===============        // is it a function assignment?        } elseif (preg_match('/^s*([a-z]w*)s*(s*([a-z]w*(?:s*,s*[a-z]w*)*)s*)s*=s*(.+)$/', $expr, $matches)) { $fnn = $matches[1]; // get the function name if (in_array($matches[1], $this->fb)) { // make sure it isn't built in     return $this->trigger("cannot redefine built-in function '$matches[1]()'"); } $args = explode(",", preg_replace("/s+/", "", $matches[2])); // get the arguments if (($stack = $this->nfx($matches[3])) === false) return false; // see if it can be converted to postfix for ($i = 0; $i<count($stack); $i++) { // freeze the state of the non-argument variables     $token = $stack[$i];     if (preg_match('/^[a-z]w*$/', $token) and !in_array($token, $args)) {         if (array_key_exists($token, $this->v)) {  $stack[$i] = $this->v[$token];         } else {  return $this->trigger("undefined variable '$token' in function definition");         }     } } $this->f[$fnn] = array('args'=>$args, 'func'=>$stack); return true;        //===============        } else { return $this->pfx($this->nfx($expr)); // straight up evaluation, woo        }    }    function vars() {        $output = $this->v;        unset($output['pi']);        unset($output['e']);        return $output;    }    function funcs() {        $output = array();        foreach ($this->f as $fnn=>$dat) $output[] = $fnn . '(' . implode(',', $dat['args']) . ')';        return $output;    }    //===================== HERE BE INTERNAL METHODS ====================\    // Convert infix to postfix notation    function nfx($expr) {        $index = 0;        $stack = new evalMathStack;        $output = array(); // postfix form of expression, to be passed to pfx()        $expr = trim(strtolower($expr));        $ops   = array('+', '-', '*', '/', '^', '_');        $ops_r = array('+'=>0,'-'=>0,'*'=>0,'/'=>0,'^'=>1); // right-associative operator?          $ops_p = array('+'=>0,'-'=>0,'*'=>1,'/'=>1,'_'=>1,'^'=>2); // operator precedence        $expecting_op = false; // we use this in syntax-checking the expression         // and determining when a - is a negation        if (preg_match("/[^ws+*^/().,-]/", $expr, $matches)) { // make sure the characters are all good return $this->trigger("illegal character '{$matches[0]}'");        }        while(1) { // 1 Infinite Loop ;) $op = substr($expr, $index, 1); // get the first character at the current index // find out if we're currently at the beginning of a number/variable/function/parenthesis/operand $ex = preg_match('/^([a-z]w*(?|d+(?:.d*)?|.d+|()/', substr($expr, $index), $match); //=============== if ($op == '-' and !$expecting_op) { // is it a negation instead of a minus?     $stack->push('_'); // put a negation on the stack     $index++; } elseif ($op == '_') { // we have to explicitly deny this, because it's legal on the stack      return $this->trigger("illegal character '_'"); // but not in the input expression //=============== } elseif ((in_array($op, $ops) or $ex) and $expecting_op) { // are we putting an operator on the stack?     if ($ex) { // are we expecting an operator but have a number/variable/function/opening parethesis?         $op = '*'; $index--; // it's an implicit multiplication     }     // heart of the algorithm:     while($stack->count > 0 and ($o2 = $stack->last()) and in_array($o2, $ops) and ($ops_r[$op] ? $ops_p[$op] < $ops_p[$o2] : $ops_p[$op] <= $ops_p[$o2])) {         $output[] = $stack->pop(); // pop stuff off the stack into the output     }     // many thanks: http://en.wikipedia.org/wiki/Reverse_Polish_notation#The_algorithm_in_detail     $stack->push($op); // finally put OUR operator onto the stack     $index++;     $expecting_op = false; //=============== } elseif ($op == ')' and $expecting_op) { // ready to close a parenthesis?     while (($o2 = $stack->pop()) != '(') { // pop off the stack back to the last (         if (is_null($o2)) return $this->trigger("unexpected ')'");         else $output[] = $o2;     }     if (preg_match("/^([a-z]w*)($/", $stack->last(2), $matches)) { // did we just close a function?         $fnn = $matches[1]; // get the function name         $arg_count = $stack->pop(); // see how many arguments there were (cleverly stored on the stack, thank you)         $output[] = $stack->pop(); // pop the function and push onto the output         if (in_array($fnn, $this->fb)) { // check the argument count  if($arg_count > 1)      return $this->trigger("too many arguments ($arg_count given, 1 expected)");         } elseif (array_key_exists($fnn, $this->f)) {  if ($arg_count != count($this->f[$fnn]['args']))      return $this->trigger("wrong number of arguments ($arg_count given, " . count($this->f[$fnn]['args']) . " expected)");         } else { // did we somehow push a non-function on the stack? this should never happen  return $this->trigger("internal error");         }     }     $index++; //=============== } elseif ($op == ',' and $expecting_op) { // did we just finish a function argument?     while (($o2 = $stack->pop()) != '(') {          if (is_null($o2)) return $this->trigger("unexpected ','"); // oops, never had a (         else $output[] = $o2; // pop the argument expression stuff and push onto the output     }     // make sure there was a function     if (!preg_match("/^([a-z]w*)($/", $stack->last(2), $matches))         return $this->trigger("unexpected ','");     $stack->push($stack->pop()+1); // increment the argument count     $stack->push('('); // put the ( back on, we'll need to pop back to it again     $index++;     $expecting_op = false; //=============== } elseif ($op == '(' and !$expecting_op) {     $stack->push('('); // that was easy     $index++;     $allow_neg = true; //=============== } elseif ($ex and !$expecting_op) { // do we now have a function/variable/number?     $expecting_op = true;     $val = $match[1];     if (preg_match("/^([a-z]w*)($/", $val, $matches)) { // may be func, or variable w/ implicit multiplication against parentheses...         if (in_array($matches[1], $this->fb) or array_key_exists($matches[1], $this->f)) { // it's a func  $stack->push($val);  $stack->push(1);  $stack->push('(');  $expecting_op = false;         } else { // it's a var w/ implicit multiplication  $val = $matches[1];  $output[] = $val;         }     } else { // it's a plain old var or num         $output[] = $val;     }     $index += strlen($val); //=============== } elseif ($op == ')') { // miscellaneous error checking     return $this->trigger("unexpected ')'"); } elseif (in_array($op, $ops) and !$expecting_op) {     return $this->trigger("unexpected operator '$op'"); } else { // I don't even want to know what you did to get here     return $this->trigger("an unexpected error occured"); } if ($index == strlen($expr)) {     if (in_array($op, $ops)) { // did we end with an operator? bad.         return $this->trigger("operator '$op' lacks operand");     } else {         break;     } } while (substr($expr, $index, 1) == ' ') { // step the index past whitespace (pretty much turns whitespace      $index++;       // into implicit multiplication if no operator is there) }        }         while (!is_null($op = $stack->pop())) { // pop everything off the stack and push onto output if ($op == '(') return $this->trigger("expecting ')'"); // if there are (s on the stack, ()s were unbalanced $output[] = $op;        }        return $output;    }    // evaluate postfix notation    function pfx($tokens, $vars = array()) {        if ($tokens == false) return false;        $stack = new evalMathStack;        foreach ($tokens as $token) { // nice and easy // if the token is a binary operator, pop two values off the stack, do the operation, and push the result back on if (in_array($token, array('+', '-', '*', '/', '^'))) {     if (is_null($op2 = $stack->pop())) return $this->trigger("internal error");     if (is_null($op1 = $stack->pop())) return $this->trigger("internal error");     switch ($token) {         case '+':  $stack->push($op1+$op2); break;         case '-':  $stack->push($op1-$op2); break;         case '*':  $stack->push($op1*$op2); break;         case '/':  if ($op2 == 0) return $this->trigger("division by zero");  $stack->push($op1/$op2); break;         case '^':  $stack->push(pow($op1, $op2)); break;     } // if the token is a unary operator, pop one value off the stack, do the operation, and push it back on } elseif ($token == "_") {     $stack->push(-1*$stack->pop()); // if the token is a function, pop arguments off the stack, hand them to the function, and push the result back on } elseif (preg_match("/^([a-z]w*)($/", $token, $matches)) { // it's a function!     $fnn = $matches[1];     if (in_array($fnn, $this->fb)) { // built-in function:         if (is_null($op1 = $stack->pop())) return $this->trigger("internal error");         $fnn = preg_replace("/^arc/", "a", $fnn); // for the 'arc' trig synonyms         if ($fnn == 'ln') $fnn = 'log';         eval('$stack->push(' . $fnn . '($op1));'); // perfectly safe eval()     } elseif (array_key_exists($fnn, $this->f)) { // user function         // get args         $args = array();         for ($i = count($this->f[$fnn]['args'])-1; $i >= 0; $i--) {  if (is_null($args[$this->f[$fnn]['args'][$i]] = $stack->pop())) return $this->trigger("internal error");         }         $stack->push($this->pfx($this->f[$fnn]['func'], $args)); // yay... recursion!!!!     } // if the token is a number or variable, push it on the stack } else {     if (is_numeric($token)) {         $stack->push($token);     } elseif (array_key_exists($token, $this->v)) {         $stack->push($this->v[$token]);     } elseif (array_key_exists($token, $vars)) {         $stack->push($vars[$token]);     } else {         return $this->trigger("undefined variable '$token'");     } }        }        // when we're out of tokens, the stack should have a single element, the final result        if ($stack->count != 1) return $this->trigger("internal error");        return $stack->pop();    }    // trigger an error, but nicely, if need be    function trigger($msg) {        $this->last_error = $msg;        if (!$this->suppress_errors) trigger_error($msg, E_USER_WARNING);        return false;    }}// for internal useclass evalMathStack {    var $stack = array();    var $count = 0;    function push($val) {        $this->stack[$this->count] = $val;        $this->count++;    }    function pop() {        if ($this->count > 0) { $this->count--; return $this->stack[$this->count];        }        return null;    }    function last($n=1) {        return $this->stack[$this->count-$n];    }}

编辑： 抖动想要支持反向抛光表示法的版本。让我想起了我上HP计算器的大学时代:)

    <?php        class RPNstack    {        var $data=array();        var $compare=0;        function pop() {return array_shift ($this->data);}        function push($x) {array_unshift($this->data, $x);}        function count() {return count($this->data);}        function first() {return $this->data[0];}        function top() {return end($this->data);}  //last element of         function swap() { // interchange tow elements $t = $this->data[1]; $this->data[1] = $this->data[0]; $this->data[0] = $t; }        function dup() {  // put a copy of X element in the stack array_unshift($this->data, $this->data[0]); }        function dump(){ // dump array data for debuging print_r($this->data); }        function parse($tok)  // execute actions with the stack for each token        { $r = null; $tok = strtoupper(trim($tok)); //$this->dump(); // this line is for debugging purpose only switch ($tok) :     // FIRST "IF THEN" AND OTHER FLOW ConTROLS     case ('THEN'): break;     case('IF'):         if ($this->pop() == 0) do {  // if condition is false do nothing until "THEN"  $tok = strtoupper(strtok (" "));  } while ($tok <> "THEN");  // IF THERE IS NO "THEN" THIS SHALL BE AN ENLESS LOOP         break;     //   basic math operators   //OPERADORES MATEMATICOS BASICOS     case('+'):         $r = $this->pop() + $this->pop();         // $r = array_shift($this->data) + array_shift($this->data);  // is more efficient but less understable         break;  case('-'):         $r = $this->pop(); $r = $this->pop()-$r;         break;     case('*'):         $r = $this->pop() *  $this->pop();         break;     case('/'):         $r = $this->pop(); $r = $this->pop() / $r;         break;     // stack operators  //OPERADORES DE PILA       case ('DUP'):         $r=$this->dup();         break;     case ('SWAP'):         $this->swap();         break;     // COMPARISON OPERATORS     case ('='):         if ($this->data[0] == $this->data[1]) $r = $this->push(1);         else $r = $this->push(0);         break;     case ('<>'):         if ($this->data[0] <> $this->data[1]) $r = $this->push(1);         else $r = $this->push(0);         break;     case ('<'):         if ($this->data[0] < $this->data[1]) $r = $this->push(1);else $r = $this->push(0);    break;     case ('>'):         if ($this->data[0] > $this->data[1])  $r = $this->push(1);else $r = $this->push(0);    break;     case ('>='):         if ($this->data[0] >= $this->data[1])  $r = $this->push(1);else $r = $this->push(0);    break;     case ('<='):         if ($this->data[0] <= $this->data[1])  $r = $this->push(1);else $r = $this->push(0);    break;     // WARNING FOR NON IMPLEMENTED FUNCTIONS     default:  return sprintf('I don't know how to "%s" ', $tok); endswitch; if (!is_null($r)) $this->push($r);  return $r;        } // parse        function parse_line($cadena)        { $tok = strtok ($cadena," "); while ($tok!= '') {     if (is_numeric ($tok)) {         $this->push($tok);     } else {         $r = $this->parse($tok);     }     $tok = strtok (" "); } return $r;        }    } // class RPN    ?>