字符串输出：C#格式或concat？

假设您想要输出或压缩字符串。您喜欢以下哪种款式

• var p=new{FirstName=“Bill”，LastName=“Gates”}
  

• Console.WriteLine（“{0}{1}”，p.FirstName，p.LastName）
  

• Console.WriteLine（p.FirstName+“”+p.LastName）
  

您是更喜欢使用格式还是只使用concat字符串？你最喜欢什么？其中一个会伤到你的眼睛吗

你有没有合理的理由使用其中一个而不是另一个

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我会选择第二个。

就我个人而言，第二个是因为您使用的所有东西都是按直接顺序输出的。而对于第一个变量，您必须将{0}和{1}与适当的var相匹配，这很容易出错

<>至少它不如C++ SpaveTF那么坏，如果你得到变量类型错误，整个事情就会爆炸。

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另外，由于第二个是内联的，它不必对所有{0}事物进行任何搜索和替换，因此后者应该更快。。。虽然我不确定。

我认为这在很大程度上取决于输出的复杂程度。我倾向于选择当时效果最好的方案

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根据作业选择正确的工具：D，以看起来最干净的为准

对于非常简单的操作，我会使用串联，但一旦超过2或3个元素，格式就变得更合适了

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选择String.Format的另一个原因是.NET字符串是不可变的，这样做会创建较少的临时/中间副本。

我也喜欢第二个，但目前我没有支持该位置的合理参数。

通常我更喜欢前者，尤其是当字符串变长时，它更容易阅读

我认为另一个好处是性能，因为后者在将最后一个字符串传递给Console.Write方法之前实际上执行了两个字符串创建语句。Format在封面下使用了StringBuilder，因此避免了多次连接

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但是，应该注意的是，如果传递给String.Format（以及其他类似于Console.Write的方法）的参数是值类型，那么它们在传递之前将被装箱，这可以提供其自身的性能影响

对于基本字符串连接，我通常使用第二种样式-更容易阅读和更简单。但是，如果我要进行更复杂的字符串组合，我通常会选择string.Format

格式保存了大量的引号和加号

Console.WriteLine("User {0} accessed {1} on {2}.", user.Name, fileName, timestamp);
vs
Console.WriteLine("User " + user.Name + " accessed " + fileName + " on " + timestamp + ".");

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虽然只保存了几个字符，但我认为，在本例中，格式使其更加清晰。

在这样一个简单的场景中，连接字符串是很好的-任何比这更复杂的东西都更复杂，即使是LastName，FirstName。使用这种格式，您可以一目了然地看到在读取代码时字符串的最终结构是什么，通过串联，几乎不可能立即识别最终结果（除了像这样一个非常简单的示例）

从长远来看，这意味着，当您回来更改字符串格式时，您将能够弹出并对格式字符串进行一些调整，或者皱起眉头，开始在混合了文本的各种属性访问器之间移动，这更可能带来问题

如果您使用的是.NET 3.5，则可以使用扩展方法，并获得一种简单流畅的即兴语法，如下所示：

string str = "{0} {1} is my friend. {3}, {2} is my boss.".FormatWith(prop1,prop2,prop3,prop4);

最后，随着应用程序复杂性的增加，您可能会决定，要在应用程序中合理地维护字符串，您需要将它们移动到资源文件中以进行本地化，或者只是移动到静态帮助器中。如果您一直使用格式，那么这将更容易实现，并且您的代码可以非常简单地进行重构以使用

string name = String.Format(ApplicationStrings.General.InformalUserNameFormat,this.FirstName,this.LastName);

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实际上，我喜欢第一个，因为当文本中有很多变量时，我似乎更容易阅读。另外，使用string.Format（），呃，Format时更容易处理引号。下面是字符串连接的示例

格式化是“.NET”的方式。某些重构工具（例如Refactor！）甚至会建议重构concat样式代码以使用格式化样式

对于编译器来说，格式化更容易优化（尽管第二个可能会被重构以使用“Concat”方法，该方法速度很快）

格式通常更清晰易读（特别是使用“奇特”的格式）

格式化意味着对所有变量隐式调用“.ToString”，这有利于可读性

根据“有效C#”的说法，.NET的“WriteLine”和“Format”实现混乱不堪，它们自动装箱所有的值类型（这很糟糕）。“有效C#”建议显式执行“.ToString”调用，IMHO认为这是假的（请参阅）

目前，编译器未检查格式化类型提示，导致运行时错误。但是，这可以在将来的版本中进行修改

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虽然我完全理解风格偏好，并在我的第一个答案中选择了连接，部分是基于我自己的偏好，但我的部分决定是基于连接会更快的想法。因此，出于好奇，我对它进行了测试，结果令人震惊，尤其是对于这样一根小绳子

使用以下代码：

    System.Diagnostics.Stopwatch s = new System.Diagnostics.Stopwatch();

    var p = new { FirstName = "Bill", LastName = "Gates" };

    s.Start();
    Console.WriteLine("{0} {1}", p.FirstName, p.LastName);
    s.Stop();
    Console.WriteLine("Console.WriteLine(\"{0} {1}\", p.FirstName, p.LastName); took: " + s.ElapsedMilliseconds + "ms - " + s.ElapsedTicks + " ticks");

    s.Reset();
    s.Start();
    Console.WriteLine(p.FirstName + " " + p.LastName);
    s.Stop();

    Console.WriteLine("Console.WriteLine(p.FirstName + \" \" + p.LastName); took: " + s.ElapsedMilliseconds + "ms - " + s.ElapsedTicks + " ticks");

我得到了以下结果：

Bill Gates
Console.WriteLine("{0} {1}", p.FirstName, p.LastName); took: 2ms - 7280 ticks
Bill Gates
Console.WriteLine(p.FirstName + " " + p.LastName); took: 0ms - 67 ticks

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使用格式化方法的速度要慢100多倍！！连接甚至没有注册为1ms，这就是为什么我也会输出计时器的节拍。

我会使用String.Format，但我也会在资源文件中使用Format字符串，这样它就可以被其他语言本地化。使用简单的字符串concat不允许这样做。显然，如果您不需要对该字符串进行本地化，那么就没有理由考虑这个问题。这真的取决于我使用的字符串

Console.WriteLine(String.Concat(p.FirstName," ",p.LastName));

Bill Gates
Console.WriteLine(p.FirstName + " " + p.LastName); took: 8ms - 30488 ticks
Bill Gates
Console.WriteLine("{0} {1}", p.FirstName, p.LastName); took: 0ms - 182 ticks

Bill Gates
Console.WriteLine(FirstName + " " + LastName); took: 5ms - 20335 ticks
Bill Gates
Console.WriteLine(FirstName + " " + LastName); took: 0ms - 156 ticks
Bill Gates
Console.WriteLine(FirstName + " " + LastName); took: 0ms - 122 ticks
Bill Gates
Console.WriteLine("{0} {1}", FirstName, LastName); took: 0ms - 181 ticks
Bill Gates
Console.WriteLine("{0} {1}", FirstName, LastName); took: 0ms - 122 ticks
Bill Gates
String.Concat(FirstName, " ", LastName); took: 0ms - 142 ticks
Bill Gates
String.Concat(FirstName, " ", LastName); took: 0ms - 117 ticks

Console.WriteLine("{0} {1}", p.FirstName, p.LastName); took (avg): 0ms - 689 ticks
Console.WriteLine(p.FirstName + " " + p.LastName); took (avg): 0ms - 683 ticks

Stopwatch s = new Stopwatch();

var p = new { FirstName = "Bill", LastName = "Gates" };

//First print to remove the initial cost
Console.WriteLine(p.FirstName + " " + p.LastName);
Console.WriteLine("{0} {1}", p.FirstName, p.LastName);

int n = 100000;
long fElapsedMilliseconds = 0, fElapsedTicks = 0, cElapsedMilliseconds = 0, cElapsedTicks = 0;

for (var i = 0; i < n; i++)
{
    s.Start();
    Console.WriteLine(p.FirstName + " " + p.LastName);
    s.Stop();
    cElapsedMilliseconds += s.ElapsedMilliseconds;
    cElapsedTicks += s.ElapsedTicks;
    s.Reset();
    s.Start();
    Console.WriteLine("{0} {1}", p.FirstName, p.LastName);
    s.Stop();
    fElapsedMilliseconds += s.ElapsedMilliseconds;
    fElapsedTicks += s.ElapsedTicks;
    s.Reset();
}

Console.Clear();

Console.WriteLine("Console.WriteLine(\"{0} {1}\", p.FirstName, p.LastName); took (avg): " + (fElapsedMilliseconds / n) + "ms - " + (fElapsedTicks / n) + " ticks");
Console.WriteLine("Console.WriteLine(p.FirstName + \" \" + p.LastName); took (avg): " + (cElapsedMilliseconds / n) + "ms - " + (cElapsedTicks / n) + " ticks");

Stopwatch s = new Stopwatch();

var p = new { FirstName = "Bill", LastName = "Gates" };

int n = 1000000;
long fElapsedMilliseconds = 0, fElapsedTicks = 0, cElapsedMilliseconds = 0, cElapsedTicks = 0;

string result;
s.Start();
for (var i = 0; i < n; i++)
    result = (p.FirstName + " " + p.LastName);
s.Stop();
cElapsedMilliseconds = s.ElapsedMilliseconds;
cElapsedTicks = s.ElapsedTicks;
s.Reset();
s.Start();
for (var i = 0; i < n; i++)
    result = string.Format("{0} {1}", p.FirstName, p.LastName);
s.Stop();
fElapsedMilliseconds = s.ElapsedMilliseconds;
fElapsedTicks = s.ElapsedTicks;
s.Reset();


Console.Clear();
Console.WriteLine(n.ToString()+" x result = string.Format(\"{0} {1}\", p.FirstName, p.LastName); took: " + (fElapsedMilliseconds) + "ms - " + (fElapsedTicks) + " ticks");
Console.WriteLine(n.ToString() + " x result = (p.FirstName + \" \" + p.LastName); took: " + (cElapsedMilliseconds) + "ms - " + (cElapsedTicks) + " ticks");
Thread.Sleep(4000);

        s.Start();
        for (var i = 0; i < n; i++)
            result = string.Concat(p.FirstName, " ", p.LastName);
        s.Stop();
        ceElapsedMilliseconds = s.ElapsedMilliseconds;
        ceElapsedTicks = s.ElapsedTicks;
        s.Reset();

1000000 x result = string.Format("{0} {1}", p.FirstName, p.LastName); took: 249ms - 3571621 ticks
1000000 x result = (p.FirstName + " " + p.LastName); took: 65ms - 944948 ticks
1000000 x result = string.Concat(p.FirstName, " ", p.LastName); took: 54ms - 780524 ticks

class Program {
   static void Main(string[] args) {

      var p = new { FirstName = "Bill", LastName = "Gates" };

      var tests = new[] {
         new { Name = "Concat", Action = new Action(delegate() { string x = p.FirstName + " " + p.LastName; }) },
         new { Name = "Format", Action = new Action(delegate() { string x = string.Format("{0} {1}", p.FirstName, p.LastName); }) },
         new { Name = "StringBuilder", Action = new Action(delegate() {
            StringBuilder sb = new StringBuilder();
            sb.Append(p.FirstName);
            sb.Append(" ");
            sb.Append(p.LastName);
            string x = sb.ToString();
         }) }
      };

      var Watch = new Stopwatch();
      foreach (var t in tests) {
         for (int i = 0; i < 5; i++) {
            Watch.Reset();
            long Elapsed = ElapsedTicks(t.Action, Watch, 10000);
            Console.WriteLine(string.Format("{0}: {1} ticks", t.Name, Elapsed.ToString()));
         }
      }
   }

   public static long ElapsedTicks(Action ActionDelg, Stopwatch Watch, int Iterations) {
      Watch.Start();
      for (int i = 0; i < Iterations; i++) {
         ActionDelg();
      }
      Watch.Stop();
      return Watch.ElapsedTicks / Iterations;
   }
}

Concat: 406 ticks Concat: 356 ticks Concat: 411 ticks Concat: 299 ticks Concat: 266 ticks Format: 5269 ticks Format: 954 ticks Format: 1004 ticks Format: 984 ticks Format: 974 ticks StringBuilder: 629 ticks StringBuilder: 484 ticks StringBuilder: 482 ticks StringBuilder: 508 ticks StringBuilder: 504 ticks

Console.WriteLine("User {0} accessed {1} on {2}.", 
                   user.Name, fileName, timestamp);

Console.WriteLine("User " + user.Name + " accessed " + fileName + 
                  " on " + timestamp + ".");

   Console.WriteLine("{0} {1}", p.FirstName, p.LastName);

   Console.WriteLine(p.FirstName + " " + p.LastName);

Stopwatch s = new Stopwatch();

int n = 1000000;
long fElapsedMilliseconds = 0, fElapsedTicks = 0, cElapsedMilliseconds = 0, cElapsedTicks = 0, sbElapsedMilliseconds = 0, sbElapsedTicks = 0;

Random random = new Random(DateTime.Now.Millisecond);

string result;
s.Start();
for (var i = 0; i < n; i++)
    result = (random.Next().ToString() + " " + random.Next().ToString());
s.Stop();
cElapsedMilliseconds = s.ElapsedMilliseconds;
cElapsedTicks = s.ElapsedTicks;
s.Reset();

s.Start();
for (var i = 0; i < n; i++)
    result = string.Format("{0} {1}", random.Next().ToString(), random.Next().ToString());
s.Stop();
fElapsedMilliseconds = s.ElapsedMilliseconds;
fElapsedTicks = s.ElapsedTicks;
s.Reset();

StringBuilder sb = new StringBuilder();
s.Start();
for(var i = 0; i < n; i++){
    sb.Clear();
    sb.Append(random.Next().ToString());
    sb.Append(" ");
    sb.Append(random.Next().ToString());
    result = sb.ToString();
}
s.Stop();
sbElapsedMilliseconds = s.ElapsedMilliseconds;
sbElapsedTicks = s.ElapsedTicks;
s.Reset();

Console.WriteLine(n.ToString() + " x result = string.Format(\"{0} {1}\", p.FirstName, p.LastName); took: " + (fElapsedMilliseconds) + "ms - " + (fElapsedTicks) + " ticks");
Console.WriteLine(n.ToString() + " x result = (p.FirstName + \" \" + p.LastName); took: " + (cElapsedMilliseconds) + "ms - " + (cElapsedTicks) + " ticks");
Console.WriteLine(n.ToString() + " x sb.Clear();sb.Append(random.Next().ToString()); sb.Append(\" \"); sb.Append(random.Next().ToString()); result = sb.ToString(); took: " + (sbElapsedMilliseconds) + "ms - " + (sbElapsedTicks) + " ticks");
Console.WriteLine("****************");
Console.WriteLine("Press Enter to Quit");
Console.ReadLine();

1000000 x result = string.Format("{0} {1}", p.FirstName, p.LastName); took: 513ms - 1499816 ticks
1000000 x result = (p.FirstName + " " + p.LastName); took: 393ms - 1150148 ticks
1000000 x sb.Clear();sb.Append(random.Next().ToString()); sb.Append(" "); sb.Append(random.Next().ToString()); result = sb.ToString(); took: 405ms - 1185816 ticks

string s = a + "foo" + b;

string tmp1 = a;
string tmp2 = "foo" 
string tmp3 = concat(tmp1, tmp2);
string tmp4 = b;
string s = concat(tmp3, tmp4);

var name = "Bill";
var surname = "Gates";
MessageBox.Show($"Welcome to the show, {name} {surname}!");

var p = new { FirstName = "Bill", LastName = "Gates" };
var fullname = $"{p.FirstName} {p.LastName}";

var qs = string.Format("q1={0}&q2={1}&q3={2}&q4={3}&q5={4}&q6={5}", 
    someVar, anotherVarWithLongName, var3, var4, var5, var6)

var qs=$"q1={someVar}&q2={anotherVarWithLongName}&q3={var3}&q4={var4}&q5={var5}&q6={var6}";