“使用未分配的局部变量”错误，即使我分配变量吗？ [英] "Use of unassigned local variable" error even though I assign the variable?

问题描述

在下面的例子中，编译器生成一个错误使用未分配的局部变量 r ，即使我在循环中分配变量在使用它之前。为什么编译器会生成此错误？

In the example below, the compiler generates an error "Use of unassigned local variable r", even though I assign the variable in loop before using it. Why does the compiler generate this error?

static void Main(string[] args)
{
    float r;

    for (int i = 0; i < 100; i++)
        r = i; // assigned here

    Console.WriteLine(r); // error: use of unassigned local variable            
}

推荐答案

编译器会在检测到未分配变量的可能性时生成该错误。因为 for 循环的主体不能保证执行（例如 for（int i = 1; i <0; i ++）），该变量不会被视为无条件分配，因此会生成编译器错误。

The compiler will generate that error whenever it detects the possibility of an unassigned variable. Since the body of for loops are not guaranteed to execute (e.g. for(int i = 1; i < 0; i++)) the variable is not considered unconditionally assigned, and thus the compiler error is generated.

从文档：

C＃编译器不允许使用未初始化变量。如果编译器检测到可能未初始化的变量的使用，则会生成编译器错误CS0165。有关详细信息，请参阅字段（C＃编程指南）。请注意，当编译器遇到可能导致使用未分配变量的构造时，即使您的特定代码不存在，也会生成此错误。这避免了过度复杂的确定分配规则的必要性。

The C# compiler does not allow the use of uninitialized variables. If the compiler detects the use of a variable that might not have been initialized, it generates compiler error CS0165. For more information, see Fields (C# Programming Guide). Note that this error is generated when the compiler encounters a construct that might result in the use of an unassigned variable, even if your particular code does not. This avoids the necessity of overly-complex rules for definite assignment.

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