C在哪里不是C ++的子集？ [英] Where is C not a subset of C++?

问题描述

我读过很多书，其中C是C ++的子集。

I read in a lot of books that C is a subset of C++.

有些书说C是C ++的子集，除了一些小细节。

Some books say that C is a subset of C++, except for the little details.

什么情况下代码将在C中而不是C ++编译？

What are some cases when code will compile in C, but not C++?

推荐答案

如果比较 C89 和 C ++ ，这是几件事

If you compare C89 with C++ then here are a couple of things

int n;
int n; // ill-formed: n already defined

int []和int [N]不兼容（否C ++中的兼容类型）

int[] and int[N] not compatible (no compatible types in C++)

int a[1];
int (*ap)[] = &a; // ill-formed: a does not have type int[]

没有K&R函数定义样式

No K&R function definition style

int b(a) int a; { } // ill-formed: grammar error

嵌套结构在C ++中具有类作用域

Nested struct has class-scope in C++

struct A { struct B { int a; } b; int c; };
struct B b; // ill-formed: b has incomplete type (*not* A::B)

无默认值int

No default int

auto a; // ill-formed: type-specifier missing

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C99添加了很多其他情况

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C99 adds a whole lot of other cases

// ill-formed: invalid syntax
void f(int p[static 100]) { }

没有可变长度的数组

No variable length arrays

// ill-formed: n is not a constant expression
int n = 1;
int an[n];

没有灵活的数组成员

No flexible array member

// ill-formed: fam has incomplete type
struct A { int a; int fam[]; }; 

没有限制限定符来帮助别名分析

No restrict qualifier for helping aliasing analysis

// ill-formed: two names for one parameter?
void copy(int *restrict src, int *restrict dst);

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