为什么汽车A = 1;用C编译？ [英] Why does auto a=1; compile in C?

问题描述

在code：

int main(void)
{
    auto a=1;
    return 0;
}

被编译而不被微软的Visual Studio 2012中的编译器，当文件有.c扩展名错误。我一直认为，当你使用.c扩展名，编译应根据C语法可以了，不是C ++。此外，据我所知没有一个类型的汽车被允许的仅在C ++中，因为C ++ 11，它意味着该类型从初始化推断出来。

gets compiled without errors by the MS Visual Studio 2012 compiler, when the file has the .c extension. I have always thought that when you use the .c extension, compilation should be according to the C syntax, and not C++. Moreover, as far as I know auto without a type is allowed only in C++ since C++11, where it means that the type is deduced from the initializer.

这是不是意味着我的编译器是不是坚持C，或者是code实际上是在C语言是否正确？

Does that mean that my compiler isn't sticking to C, or is the code actually correct in C-language?

推荐答案

汽车是一个旧的C关键字，意思是本地范围。 汽车A 相同汽车int类型的，因为本地范围是一个函数内声明的变量默认，这也是在本实施例相同 int类型的

auto is an old C keyword that means "local scope". auto a is the same as auto int a, and because local scope is the default for a variable declared inside a function, it's also the same as int a in this example.

此关键字实际上是从C的predecessor ​​B，那里没有基本类型的后遗症：一切 INT ，指向 INT ，数组 INT 。（*）的声明是，要么汽车或 EXTRN [原文]。 C派生出一切为 INT 作为默认规则，所以你可以用

This keyword is actually a leftover from C's predecessor B, where there were no base types: everything was int, pointer to int, array of int.(*) Declarations would be either auto or extrn [sic]. C inherited the "everything is int" as a default rule, so you could declare integers with

auto a;
extern b;
static c;

ISO C摆脱了这一点，但很多编译器仍然接受它向后兼容。如果它似乎陌生，那么你应该认识到，相关的规则是在工作中

ISO C got rid of this, but many compilers still accept it for backward compatibility. If it seems unfamiliar, then you should realise that a related rule is at work in

unsigned d;  // actually unsigned int

这仍然是常见于现代$​​ C $ C。

which is still common in modern code.

C ++ 11重复使用关键字，如果有C ++程序员用同本义这几年，它的类型推断。这主要是安全的，因为一切 INT 从C规则已经下降在C ++ 98;打破的唯一事情是自动T A ，没有人使用反正这是。 （某处在他的报纸上的语言的历史，在这个Stroustrup的意见，但现在我无法找到确切的参考。）

C++11 reused the keyword, which few if any C++ programmers were using with the original meaning, for its type inference. This is mostly safe because the "everything is int" rule from C had already been dropped in C++98; the only thing that breaks is auto T a, which no-one was using anyway. (Somewhere in his papers on the history of the language, Stroustrup comments on this, but I can't find the exact reference right now.)

（*）字符串B中的处理很有意思：你会使用 INT 的数组并在每个成员打包多个字符。乙实际上 BCPL 是用不同的语法。

(*) String handling in B was interesting: you'd use arrays of int and pack multiple characters in each member. B was actually BCPL with different syntax.

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