UNIX Message Queue

Applications Programming
1

Hello !!!!! I have a simple question but i can't find the answer anywhere hope to meet it here.

Why it is a bad idea to pass pointers through message queues ?
Most structs i see all of their char types are arrays... Is it becase having pointers means we could possibily send wrong bytes ?
For instances :

typedef struct {
int mtype; // 4 Bytes
char *text // 1Bytes
} bufferA;

typedef struct {
int mtype; // 4 Bytes
char text[10]; // 10Bytes
} bufferB;

On both structs text is "Hello World\0", on bufferA we would only send 1Byte which maybe means we would only send H while on bufferB we would send the whole sentence, "Hello World" . Is that correct ?

2

My best guess is that the application receiving the pointer via the message queue has not yet allocated memory for the length of the string.

Just a guess... however. It has been a long time since I worked with message queues.

3

Pointers reference process memory in the sending porocess. There is no guarantee that the pointer the receiver process gets will reference the same thing or anything at all.

Message queues work by passing data values not pointers to data.

Are you thinking about the msgtype value ( the first long in the msg struct). You can use this like a "pointer" - if you create message types 1...42 and use them only once, then you can get message id #13. But the processes have to agree ahead of time how many messages.