我可以在 for 循环的初始化中声明不同类型的变量

问题描述

为什么这段 C++ 代码在 VS2010 下无法编译:

Why does this C++ code not compile under VS2010:

for ( int a = 0, short b = 0; a < 10; ++a, ++b ) {}

虽然这个是:

short b = 0;
for ( int a = 0; a < 10; ++a, ++b ) {}

是否禁止在for循环初始化器中声明两个不同类型的变量?如果是这样，您如何解决它?

Is the declaration of two variables of different types inside the for-loop initializer prohibited? If so, how can you work around it?

推荐答案

是的，这是被禁止的.就像否则你不能在一个声明语句中声明不同类型的变量一样(编辑:以@MrLister 提到的声明符修饰符为模).您可以声明结构

Yes, that is prohibited. Just as otherwise you cannot declare variables of differing types in one declaration statement (edit: modulo the declarator modifiers that @MrLister mentions). You can declare structs

for (struct { int a = 0; short b = 0; } d; d.a < 10; ++d.a, ++d.b ) {}

C++03 代码:

for (struct { int a; short b; } d = { 0, 0 }; d.a < 10; ++d.a, ++d.b ) {}

当然，当全部为0时，您可以完全省略初始化器并编写= { }.

Of course when all are 0, you can omit the initializers altogether and write = { }.

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