我想截断一个字符串,使其长度不超过给定值。我正在向数据库表写入数据,并希望确保写入的值满足列数据类型的约束。

例如,如果我能写以下内容,那就太好了:

string NormalizeLength(string value, int maxLength)
{
    return value.Substring(0, maxLength);
}

不幸的是,这会引发异常,因为maxLength通常超过字符串值的边界。当然,我可以写一个像下面这样的函数,但我希望这样的东西已经存在了。

string NormalizeLength(string value, int maxLength)
{
    return value.Length <= maxLength ? value : value.Substring(0, maxLength);
} 

执行此任务的难以捉摸的API在哪里?有吗?


当前回答

以@CaffGeek为例进行简化:

public static string Truncate(this string value, int maxLength)
    {
        return string.IsNullOrEmpty(value) ? value : value.Substring(0, Math.Min(value.Length, maxLength));
    }

其他回答

基于这个和这个,这里有两个版本,将适用于“到”值的负值。第一个函数不允许负数无声地设置为0:

public static string Truncate(this string value, int maxLength)
{
    return string.IsNullOrEmpty(value) ?
        value :
        value.Substring(0, Math.Max(0, Math.Min(value.Length, maxLength)));
}

这是一个循环:

private static int Mod(this int a, int n) => (((a %= n) < 0) ? n : 0) + a;

public static string Truncate(this string value, int maxLength)
{
    return string.IsNullOrEmpty(value) ?
        value :
        value.Substring(0, maxLength.Mod(value.Length));
}

以防这里没有足够的答案,这里是我的:)

public static string Truncate(this string str, 
                              int totalLength, 
                              string truncationIndicator = "")
{
    if (string.IsNullOrEmpty(str) || str.Length < totalLength) 
        return str;

    return str.Substring(0, totalLength - truncationIndicator.Length) 
           + truncationIndicator;
}

使用方法:

"I use it like this".Truncate(5,"~")

TruncateString

public static string _TruncateString(string input, int charaterlimit)
{
    int characterLimit = charaterlimit;
    string output = input;

    // Check if the string is longer than the allowed amount
    // otherwise do nothing
    if (output.Length > characterLimit && characterLimit > 0)
    {
        // cut the string down to the maximum number of characters
        output = output.Substring(0, characterLimit);
        // Check if the character right after the truncate point was a space
        // if not, we are in the middle of a word and need to remove the rest of it
        if (input.Substring(output.Length, 1) != " ")
        {
            int LastSpace = output.LastIndexOf(" ");

            // if we found a space then, cut back to that space
            if (LastSpace != -1)
            {
                output = output.Substring(0, LastSpace);
            }
        }
        // Finally, add the "..."
        output += "...";
    }
    return output;
}

2016年c#字符串仍然没有截断方法。 但是-使用c# 6.0语法:

public static class StringExtension
{
  public static string Truncate(this string s, int max) 
  { 
    return s?.Length > max ? s.Substring(0, max) : s ?? throw new ArgumentNullException(s); 
  }
}

它就像一个魔法:

"Truncate me".Truncate(8);
Result: "Truncate"

所有其他答案都没有考虑到Span的性能,它比。net中字符串类型的Substring的性能更好

如果你还不知道有一个版本的系统。内存(为以下情况提供了Span, ReadOnlySpan, Memory和ReadOnlyMemory:

这样的简单实现可以如下所示:

public static string Truncate(this string value, int maxLength)
{
    if (!string.IsNullOrEmpty(value) && value.Length > maxLength)
    {
        return value.AsSpan(0, maxLength).ToString(); /* Note the use of AsSpan instead of Substring. */
    }

    return value;
}

该方法理论上可以返回Span<char>,以避免使用Span<T>的ToString()成员分配新字符串。

The BCL itself internally uses Span's, ReadOnlySpan's, Memory's, and ReadOnlyMemory's where possible to avoid issues and to help optimize the code, especially when you compile arrays that are known at compile time and so using an property that returns that new'd up array as an ReadOnlySpan<byte> actually optimizes the code at runtime as then the JIT would not call memcpy on the data and instead uses it since it just returns a Span and as such is a window to the data that is already allocated ahead of time resulting in:

更少的分配。 更少的分配时间。 使代码总体上更快地使用。