struct和typedef struct在C和C++中的区别

There are _3_ ways of using struct.  Here are all 3 different ways in a
program, with comments. Hope this clears up confusion.

typedef struct {
         int data;
         int text;
} S1;
//  This will define a typedef for S1, in both C and in C++

struct S2 {
         int data;
         int text;
};
// This will define a typedef for S2 ONLY in C++, will create error in C (but use struct S2 can solve it).

struct {
         int data;
         int text;
} S3;
// This will declare S3 to be a variable of type struct.
// This is VERY different from the above two.
// This does not define a type. The above two defined type S1 and S2.
// This tells compiler to allocate memory for variable S3

void main()
{
 S1 mine1; // this will work, S1 is a typedef.
 S2 mine2; // this will work, S2 is also a typedef.
 S3 mine3; // this will NOT work, S3 is not a typedef.

 S1.data = 5;  // Will give error because S1 is only a typedef.
 S2.data = 5;  // Will also give error because S1 is only a typedef.
 S3.data = 5;  // This will work, because S3 is a variable.
}
// That's how they different stuff are handy.

also !!!!!!!!!!! This next bit is important for people who using linked
lists etc.

struct S6 {
 S6* ptr;
};
// This works, in C++ only.

typedef struct {
 S7* ptr;
} S7;
// Although you would think this does the same thing in C OR C++....
// This DOES NOT work in C nor C++ !!!

事实上，要依编译器的标准为准，例如，在VC++中，允许这样的定义：

typedef struct s1

{

int a;

struct s1 *p;

}s3;

这时，s3是做为一个新类型的，不是结构变量。而如果这样声明：

struct s1

{

int a;

struct s1 *p;

}s3;

s3就做为一个结构变量，而不是一个类型。