我正在开发一个计算器，它接受字符串表达式并对其进行评估。我有一个函数，它使用正则表达式搜索数学函数的表达式，检索参数，查找函数名称并对其进行评估。我遇到的问题是，如果我知道会有多少参数，我只能这样做，我无法正确使用正则表达式。如果我只是按字符拆分(and)字符的内容，,那么我不能在该参数中调用其他函数。
这是函数匹配模式：\b([a-z][a-z0-9_]*)\((..*)\)\b
它只适用于一个参数，我可以为每个参数创建一个组，不包括嵌套函数内部的参数吗？例如，它将匹配：并为：和func1(2 * 7, func2(3, 5))创建捕获组：2 * 7func2(3, 5)
这是我用来评估表达式的函数：
/// <summary>
/// Attempts to evaluate and store the result of the given mathematical expression.
/// </summary>
public static bool Evaluate(string expr, ref double result)
{
expr = expr.ToLower();
try
{
// Matches for result identifiers, constants/variables objects, and functions.
MatchCollection results = Calculator.PatternResult.Matches(expr);
MatchCollection objs = Calculator.PatternObjId.Matches(expr);
MatchCollection funcs = Calculator.PatternFunc.Matches(expr);
// Parse the expression for functions.
foreach (Match match in funcs)
{
System.Windows.Forms.MessageBox.Show("Function found. - " + match.Groups[1].Value + "(" + match.Groups[2].Value + ")");
int argCount = 0;
List<string> args = new List<string>();
List<double> argVals = new List<double>();
string funcName = match.Groups[1].Value;
// Ensure the function exists.
if (_Functions.ContainsKey(funcName)) {
argCount = _Functions[funcName].ArgCount;
} else {
Error("The function '"+funcName+"' does not exist.");
return false;
}
// Create the pattern for matching arguments.
string argPattTmp = funcName + "\\(\\s*";
for (int i = 0; i < argCount; ++i)
argPattTmp += "(..*)" + ((i == argCount - 1) ? ",":"") + "\\s*";
argPattTmp += "\\)";
// Get all of the argument strings.
Regex argPatt = new Regex(argPattTmp);
// Evaluate and store all argument values.
foreach (Group argMatch in argPatt.Matches(match.Value.Trim())[0].Groups)
{
string arg = argMatch.Value.Trim();
System.Windows.Forms.MessageBox.Show(arg);
if (arg.Length > 0)
{
double argVal = 0;
// Check if the argument is a double or expression.
try {
argVal = Convert.ToDouble(arg);
} catch {
// Attempt to evaluate the arguments expression.
System.Windows.Forms.MessageBox.Show("Argument is an expression: " + arg);
if (!Evaluate(arg, ref argVal)) {
Error("Invalid arguments were passed to the function '" + funcName + "'.");
return false;
}
}
// Store the value of the argument.
System.Windows.Forms.MessageBox.Show("ArgVal = " + argVal.ToString());
argVals.Add(argVal);
}
else
{
Error("Invalid arguments were passed to the function '" + funcName + "'.");
return false;
}
}
// Parse the function and replace with the result.
double funcResult = RunFunction(funcName, argVals.ToArray());
expr = new Regex("\\b"+match.Value+"\\b").Replace(expr, funcResult.ToString());
}
// Final evaluation.
result = Program.Scripting.Eval(expr);
}
catch (Exception ex)
{
Error(ex.Message);
return false;
}
return true;
}
////////////////////////////////// ---- PATTERNS ---- \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
/// <summary>
/// The pattern used for function calls.
/// </summary>
public static Regex PatternFunc = new Regex(@"([a-z][a-z0-9_]*)\((..*)\)");
如您所见，构建正则表达式以匹配参数的尝试非常糟糕。它不起作用。
我要做的就是从表达式中提取2 * 7和提取，但它也必须适用于具有不同参数计数的函数。如果有办法在不使用正则表达式的情况下做到这一点，那也很好。func2(3, 5)func1(2 * 7, func2(3, 5))