Use:

s.erase(std::remove_if(s.begin(), s.end(), my_predicate), s.end());

bool my_predicate(char c)
{
 return !(isalpha(c) || c=='_' || c==' '); // depending on you definition of special characters
}

你会得到一个干净的字符串s。

Erase()将去掉所有特殊字符，并且可以使用my_predicate()函数进行高度自定义。

public string RemoveSpecial(string evalstr)
{
StringBuilder finalstr = new StringBuilder();
            foreach(char c in evalstr){
            int charassci = Convert.ToInt16(c);
            if (!(charassci >= 33 && charassci <= 47))// special char ???
             finalstr.append(c);
            }
return finalstr.ToString();
}

我同意这个代码示例。唯一不同的是，我把它变成字符串类型的扩展方法。所以你可以在非常简单的一行或代码中使用它:

string test = "abc@#$123";
test.RemoveSpecialCharacters();

感谢Guffa的实验。

public static class MethodExtensionHelper
    {
    public static string RemoveSpecialCharacters(this string str)
        {
            StringBuilder sb = new StringBuilder();
            foreach (char c in str)
            {
                if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == '_')
                {
                    sb.Append(c);
                }
            }
            return sb.ToString();
        }
}

I had to do something similar for work, but in my case I had to filter all that is not a letter, number or whitespace (but you could easily modify it to your needs). The filtering is done client-side in JavaScript, but for security reasons I am also doing the filtering server-side. Since I can expect most of the strings to be clean, I would like to avoid copying the string unless I really need to. This let my to the implementation below, which should perform better for both clean and dirty strings.

public static string EnsureOnlyLetterDigitOrWhiteSpace(string input)
{
    StringBuilder cleanedInput = null;
    for (var i = 0; i < input.Length; ++i)
    {
        var currentChar = input[i];
        var charIsValid = char.IsLetterOrDigit(currentChar) || char.IsWhiteSpace(currentChar);

        if (charIsValid)
        {
            if(cleanedInput != null)
                cleanedInput.Append(currentChar);
        }
        else
        {
            if (cleanedInput != null) continue;
            cleanedInput = new StringBuilder();
            if (i > 0)
                cleanedInput.Append(input.Substring(0, i));
        }
    }

    return cleanedInput == null ? input : cleanedInput.ToString();
}

我觉得你的算法很有效。它是O(n)，并且只查看每个字符一次。除非你在检查它们之前神奇地知道它们的值，否则你不会比这更好。

但是，我将把StringBuilder的容量初始化为字符串的初始大小。我猜您认为的性能问题来自内存重新分配。

旁注:检查A-z并不安全。你要包括[，\，]，^，_和'…

旁注2:为了获得额外的效率，将比较按顺序排列，以减少比较的数量。(在最坏的情况下，你说的是8个比较，所以不要想太多。)这随你的预期输入而变化，但一个例子可以是:

if (str[i] >= '0' && str[i] <= 'z' && 
    (str[i] >= 'a' || str[i] <= '9' ||  (str[i] >= 'A' && str[i] <= 'Z') || 
    str[i] == '_') || str[i] == '.')

旁注3:如果出于某种原因，你真的需要它更快，那么switch语句可能更快。编译器应该为你创建一个跳转表，结果只有一个比较:

switch (str[i])
{
    case '0':
    case '1':
    .
    .
    .
    case '.':
        sb.Append(str[i]);
        break;
}

正则表达式的使用方法如下:

return Regex.Replace(strIn, @"[^\w\.@-]", "", RegexOptions.None, TimeSpan.FromSeconds(1.0));