[英]Declare and assign multiple string variables at the same time
我声明了一些空字符串,因此以后不会抛出错误。
我读过这是正确的方法:
string Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = Startdatum = Bonprioriteit = Matsoort = Dikte = Draaibaarheid = Draaiomschrijving = Orderleverdatum = Regeltaakkode = Gebruiksvoorkeur = Regelcamprog = Regeltijd = Orderrelease = "";
但这不起作用。 我收到此错误: Klantnr does not exist in the current context
。
我做错了什么?
你可以这样做:
string Camnr, Klantnr, Ordernr, Bonnr, Volgnr;// and so on.
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = string.Empty;
首先,您必须定义变量,然后才能使用它们。
你可以这样做:
string Camnr = "", Klantnr = "", ... // or String.Empty
或者你可以先声明它们,然后在下一行使用你的方式。
我称之为串联声明的一个例子:
string Camnr = "",
Klantnr = "",
Ordernr = "",
Bonnr = "",
Volgnr = "",
Omschrijving = "",
Startdatum = "",
Bonprioriteit = "",
Matsoort = "",
Dikte = "",
Draaibaarheid = "",
Draaiomschrijving = "",
Orderleverdatum = "",
Regeltaakkode = "",
Gebruiksvoorkeur = "",
Regelcamprog = "",
Regeltijd = "",
Orderrelease = "";
只是我的 2 美分,希望它可以帮助某个地方的人。
尝试:
string Camnr, Klantnr, Ordernr, Bonnr, Volgnr, Omschrijving;
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = string.Empty;
尝试
string Camnr , Klantnr , Ordernr , Bonnr , Volgnr , Omschrijving , Startdatum , Bonprioriteit , Matsoort , Dikte , Draaibaarheid , Draaiomschrijving , Orderleverdatum , Regeltaakkode , Gebruiksvoorkeur , Regelcamprog , Regeltijd , Orderrelease ;
接着
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = Startdatum = Bonprioriteit = Matsoort = Dikte = Draaibaarheid = Draaiomschrijving = Orderleverdatum = Regeltaakkode = Gebruiksvoorkeur = Regelcamprog = Regeltijd = Orderrelease = "";
string Camnr , Klantnr , Ordernr , Bonnr , Volgnr , Omschrijving , Startdatum , Bonprioriteit , Matsoort , Dikte , Draaibaarheid , Draaiomschrijving , Orderleverdatum , Regeltaakkode , Gebruiksvoorkeur , Regelcamprog , Regeltijd , Orderrelease;
Camnr = Klantnr = Ordernr = Bonnr = Volgnr = Omschrijving = Startdatum = Bonprioriteit = Matsoort = Dikte = Draaibaarheid = Draaiomschrijving = Orderleverdatum = Regeltaakkode = Gebruiksvoorkeur = Regelcamprog = Regeltijd = Orderrelease = string.Empty;
提醒一下:不允许在多个声明中使用隐式类型var
。 可能存在以下编译错误。
var Foo = 0, Bar = 0;
隐式类型的变量不能有多个声明符
相似地,
var Foo, Bar;
必须初始化隐式类型的变量
string a = "", b = a , c = a, d = a, e = a, f =a;
现在可以通过以下方式声明和初始化多个变量:
var (anInt, aFloat, aBoolean, aChar, aString, anArray, aRecordType, anObjectType) =
(1, 2.14, true, 'a', "C# is awesome!", new[] { "Asia", "Europe" } , new Country { Name = "India"}, new City { Name = "Kolkata"} );
Console.WriteLine(anInt);
Console.WriteLine(aFloat);
Console.WriteLine(aBoolean);
Console.WriteLine(aChar);
Console.WriteLine(aString);
Array.ForEach(anArray, Console.WriteLine);
Console.WriteLine(aRecordType.Name);
Console.WriteLine(anObjectType.Name);
以下是所需自定义类型的定义:
internal record Country { internal string Name {get; set;}}
internal class City { internal string Name {get; set;}}
这已经在 .NET 5/C# 9 上进行了测试。
所有信息都在现有答案中,但我个人希望有一个简洁的总结,所以这里尝试一下; 为简洁起见,这些命令使用int
变量,但它们类似地适用于任何类型,包括string
。
声明多个变量和:
int i = 0, j = 1; // declare and initialize each, single-type only.
// Note: `var` is NOT supported as of C# 8.0, but see below.
// ===
// C# 7.0+ / .NET Framework 4.7+ using syntactic sugar based on *value tuples*:
// Infer the types from the RHS tuple elements.
var (i, s) = (0, "hi");
// Explicitly type the individual variables.
(int i, string s) = (0, "hi");
int i, j; // *declare* first (`var` is NOT supported)
i = j = 42; // then *initialize*
// Single-statement alternative that is perhaps visually less obvious:
// Initialize the first variable with the desired value, then use
// the first variable to initialize the remaining ones.
int i = 42, j = i, k = i;
什么不起作用:
除非您使用值元组语法,否则不能在上述语句中使用var
,因为var
仅适用于 (a) 具有初始化值(可以从中推断出类型)的声明,以及 (b),截至C# 8.0,如果该声明是语句中唯一的声明(否则您将收到编译错误error CS0819: Implicitly-typed variables cannot have multiple declarators
)。
放置在多声明语句的最后一个变量后,才只初始化最后一个变量的初始化值:
int i, j = 1;
// initializes *only* j
相当古老的问题,但以防万一有人回去。
这不像上面的其他答案那么紧凑,但使用 Visual Studio 多行选择快捷方式 [Alt+ Shift + ↑](或其他方向)相当可读且更易于输入
string Camnr = string.Empty;
string Klantnr = string.Empty;
在新行中输入所有变量名称。 多选他们前面的一个类型“字符串”。 在它们后面多选并输入“= string.Empty;”。
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