“定义”和“定义”之间的区别和“声明”
可能的重复：
定义和声明之间有什么区别？< /a>
我试图彻底理解C中的“定义”和“声明”。
我相信这里的x已经被定义了，因为外部变量会自动初始化为0，并且定义了声明和初始化的东西。准确吗？
int x;
main() {}
在本例中根据一个x是一个定义，但是为什么呢？它没有被初始化...
int print_hello()
{
int x;
}
Possible Duplicate:
What is the difference between a definition and a declaration?
I am trying to thoroughly understand "defining" and "declaring" in C.
I believe x here is defined, since external variables are automatically initialized to 0, and something that's declared and initialized is defined. Is that accurate?
int x;
main() {}
According to one x in this case is a definition, but why? It is not being initialized...
int print_hello()
{
int x;
}
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声明是告诉编译器有一个如下所示的变量。
定义就是告诉编译器这是一个变量。
一是指事物的存在，二是事物本身。
在您的示例中，范围才是造成差异的原因。声明是在文件作用域中进行的，但在块作用域中不可能声明任何内容；因此，第二个例子是一个定义；因为，与
int x;没有什么关系了。这使得第一个示例（在文件范围内）成为某个
int x;存在的声明。要从声明中隐藏它，您需要指定为其分配一个值，从而强制分配内存。就像这样：int x = 0;C 和 C++ 在分析结构时对范围非常敏感。
Declaring is telling the compiler that there's a variable out there that looks like this.
Defining is telling the compiler that this is a variable.
One refers to the existence of a thing, the other is the thing.
In your example, the scope is what makes the difference. Declarations are made in a file scope, but in a block scope it is not possible to declare anything; therefore, the second example is a definition; because, there is nothing left to do with the
int x;.That makes the first example (in the file scope) a declaration that some
int x;exists. To covert it from a declaration, you need to specify that a value is assigned to it, forcing the memory allocation. Like so:int x = 0;C and C++ are very scope sensitive when it is analyzing constructs.
“定义”并不意味着“初始化”。这意味着某些东西被创建，而不仅仅是引用。
定义分配但不一定初始化内存。这可以带来有趣的调试。
"Define" does not mean "initialized." It means something is created, rather than just referenced.
A definition allocates but does not necessarily initialize memory. This can lead to fun debugging.
声明在 TU 中引入名称。定义为该名称实例化/分配存储。
Declaration introduces a name in a TU. Definition instantiates/allocates storage for that name.