C language Variable length message definition: Flexible array

In the process of exchange between the front and back of the game, often used to become the message body, because some content is the size of the location, such as a microblog, the content size of the microblog is unknown.

The general practice is to define a pointer of type char*, and then specify its length, as follows:

typedef struct{unsigned len;char* PData;} MSG;

The use of the time is this:

Char str[] = "Hello world!"; unsigned len = sizeof (str); msg* m = (msg*) malloc (sizeof (MSG) +len*sizeof (char)), M->len = Len;m->pdata = (char*) (m+1); memcpy (m+1, str, len); printf ("%d,%s\n", M->len, M->pdata);

Do you think the timing of char* pdata a lot more?

Because the data time is stored in m+1, we can directly get this pointer, without redefining a char* pdata to error this position.

This brings us to another problem where access is inconvenient, we cannot access it in the way of struct members, we can use a flexible array, and see:

typedef struct{unsigned LEN;CHAR data[];} Message;

That's how it's used:

message* msg = (message*) malloc (sizeof (Message) + len*sizeof (char)); Msg->len = len;memcpy (Msg->data, str, len); printf ("%d,%s\n", Msg->len, Msg->data); free (msg);

To divide the complete code comparison:

Array0.h

typedef struct{unsigned len;char* PData;} Msg;typedef struct{unsigned Len;char data[];} Message;

Main.c

Test for 0 size array#include <stdio.h> #include <stdlib.h> #include <string.h> #include "array0.h" int main () {char str[] = "Hello world!"; unsigned len = sizeof (str);//general usage msg* m = (msg*) malloc (sizeof (MSG) +len*sizeof (char)); M->len = Len;m->pdata = (char *) (m+1); memcpy (m+1, str, len);p rintf ("%d,%s\n", M->len, M->pdata); free (m);//flexible array message* msg = (message*) malloc (sizeof (Message) + len*sizeof (char)); Msg->len = len;memcpy (Msg->data, str, len);p rintf ("%d,%s\n", Msg->len, Msg->data); free (msg); System ("pause"); return 0;}

C language Variable length message definition: Flexible array