Programming Forums > Application Development > C++

rup · Apr 15th, 2006, 3:30 AM

I am in Linux, using g++ to compile.

My code looks like this:

This is the header:

class Test
{
   //...code... 
   
   public:
   void Function();
   
   //...code... 
};

In a cpp file I have the declaration:

(Toggle Plain Text)

void Test::Function(...)
{
   //....code...
}

I got this error when compiling:
....error: expected primary-expression before �void�....

What does this mean.
BTW, the code fragments are highly simplified and only a part of a programming project. But the interface is similar.
Can somebody help?

DaWei · Apr 15th, 2006, 6:54 AM

You show an error that says, "expected primary-expression before 'void'..." Then you show us a snippet with everything before 'void' snipped out....hilarious. Incidentally, that's the definition in the cpp file, the declaration is in the class. Did you mean to have those three dots in the arg list in the definition and not up in the declaration?

grumpy · Apr 15th, 2006, 8:37 AM

As Dawei said, the code snippets given do not give any useful information. It is better to find a SMALL but COMPLETE example that repeatably illustrates your problem (and post it verbatim in code tags). I recommend you read the sticky threads on "How to ask a question" as well .... they give advice on how to ask a question to increase your chances of getting a useful response.

The most common reasons the compiler would expect an expression before a function declaration or definition are a missing closing brace i.e. } or a missing semi-colon (or possibly both). But, given that you haven't provided enough information, that is only a stab in the dark.

rup · Apr 15th, 2006, 8:48 AM

Sorry for the incomplete post, should have followed intructions.
Here's the complete code:

The header gIPC.h:

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#ifndef __GIPC_H__
#define __GIPC_H__

#include "gMsg.h"

class MessageQueue
{
	private:
		int qid;
		
	public:
		MessageQueue();
		~MessageQueue();
		void MsgSnd(Msg);
		void MsgRcv(Msg);
};

#endif // __GIPC_H__

The cpp, gIPC.cpp:

(Toggle Plain Text)

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include "gIPC.h"

MessageQueue::MessageQueue()
{
	qid = msgget(key_t(1234), 0666|IPC_CREAT);
}

MessageQueue::~MessageQueue()
{
	msgctl(qid,IPC_RMID,0);
}

void MessageQueue::MsgSnd(Msg m)
{
	msgsnd(qid, void*(&m), m.GetMsgSize(),0);
}

void MessageQueue::MsgRcv(Msg m)
{
	msgrcv(qid, void*(&m), BUFSIZE, m.GetMsgType(), 0);
}

This is the error:

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rup@ubuntu:~/gui$ make
g++ -c gIPC.cpp
gIPC.cpp: In member function �void MessageQueue::MsgSnd(Msg)�:
gIPC.cpp:18: error: expected primary-expression before �void�
gIPC.cpp: In member function �void MessageQueue::MsgRcv(Msg)�:
gIPC.cpp:23: error: expected primary-expression before �void�
make: *** [gIPC.o] Error 1

InfoGeek · Apr 15th, 2006, 8:58 AM

(Toggle Plain Text)

SYSTEM CALL: msgsnd();                                                          

  PROTOTYPE: int msgsnd ( int msqid, struct msgbuf *msgp, int msgsz, int msgflg );

msgsnd function expects a struct msgbuf * as the second argument. Why are you passing a void *?

DaWei · Apr 15th, 2006, 9:05 AM

(Toggle Plain Text)

	msgsnd(qid, void*(&m), m.GetMsgSize(),0);

One doesn't declare a function's parameter type when one calls it, only when one declares or defines it. Did you perhaps mean to cast it?

rup · Apr 15th, 2006, 2:11 PM

I picked msgsnd from the book Beginning Linux Programming (Wrox).
It has the following prototype:

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int msgsnd(int msqid, const void* msg_ptr, size_t msg_sz, int msgflag);

and is called this way in an example C program in the book:

(Toggle Plain Text)

msgsnd(msgid, (void*)&some_data, MAX_TEXT, 0);

where some_data is the structure:

(Toggle Plain Text)

struct msg{
    long int msg_type;
    char text[MAX_TEXT];
};

Yes, I meant to cast it.

DaWei · Apr 15th, 2006, 2:28 PM

So, did that clear your error message or not? Inquiring members want to know. It's the fee.

rup · Apr 16th, 2006, 9:26 AM

Yes, it cleared my error message.

I hade written this:

(Toggle Plain Text)

msgrcv(qid, void*(&m), BUFSIZE, m.GetMsgType(), 0);

Because in C++ a cast is applied this way : void(variable) I had left it that way. Making it (void*)(&m) solves the problem.

grumpy · Apr 16th, 2006, 9:57 AM

Quote:

Originally Posted by rup

Because in C++ a cast is applied this way : void(variable) I had left it that way.

Rubbish. A cast is not applied "this way" in C nor in C++.

Apr 15th, 2006, 3:30 AM	#1
rup Newbie Join Date: Jul 2005 Location: India Posts: 14 Rep Power: 0	error: expected primary-expression... I am in Linux, using g++ to compile. My code looks like this: This is the header: (Toggle Plain Text) class Test { //...code... public: void Function(); //...code... }; class Test { //...code... public: void Function(); //...code... }; In a cpp file I have the declaration: (Toggle Plain Text) void Test::Function(...) { //....code... } void Test::Function(...) { //....code... } I got this error when compiling: ....error: expected primary-expression before �void�.... What does this mean. BTW, the code fragments are highly simplified and only a part of a programming project. But the interface is similar. Can somebody help?

Apr 15th, 2006, 6:54 AM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	You show an error that says, "expected primary-expression before 'void'..." Then you show us a snippet with everything before 'void' snipped out....hilarious. Incidentally, that's the definition in the cpp file, the declaration is in the class. Did you mean to have those three dots in the arg list in the definition and not up in the declaration? __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Apr 15th, 2006, 8:48 AM	#4
rup Newbie Join Date: Jul 2005 Location: India Posts: 14 Rep Power: 0	Sorry for the incomplete post, should have followed intructions. Here's the complete code: The header gIPC.h: (Toggle Plain Text) #ifndef __GIPC_H__ #define __GIPC_H__ #include "gMsg.h" class MessageQueue { private: int qid; public: MessageQueue(); ~MessageQueue(); void MsgSnd(Msg); void MsgRcv(Msg); }; #endif // __GIPC_H__ #ifndef __GIPC_H__ #define __GIPC_H__ #include "gMsg.h" class MessageQueue { private: int qid; public: MessageQueue(); ~MessageQueue(); void MsgSnd(Msg); void MsgRcv(Msg); }; #endif // __GIPC_H__ The cpp, gIPC.cpp: (Toggle Plain Text) #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #include "gIPC.h" MessageQueue::MessageQueue() { qid = msgget(key_t(1234), 0666\|IPC_CREAT); } MessageQueue::~MessageQueue() { msgctl(qid,IPC_RMID,0); } void MessageQueue::MsgSnd(Msg m) { msgsnd(qid, void(&m), m.GetMsgSize(),0); } void MessageQueue::MsgRcv(Msg m) { msgrcv(qid, void(&m), BUFSIZE, m.GetMsgType(), 0); } #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #include "gIPC.h" MessageQueue::MessageQueue() { qid = msgget(key_t(1234), 0666\|IPC_CREAT); } MessageQueue::~MessageQueue() { msgctl(qid,IPC_RMID,0); } void MessageQueue::MsgSnd(Msg m) { msgsnd(qid, void(&m), m.GetMsgSize(),0); } void MessageQueue::MsgRcv(Msg m) { msgrcv(qid, void(&m), BUFSIZE, m.GetMsgType(), 0); } This is the error: (Toggle Plain Text) rup@ubuntu:~/gui$ make g++ -c gIPC.cpp gIPC.cpp: In member function �void MessageQueue::MsgSnd(Msg)�: gIPC.cpp:18: error: expected primary-expression before �void� gIPC.cpp: In member function �void MessageQueue::MsgRcv(Msg)�: gIPC.cpp:23: error: expected primary-expression before �void� make: * [gIPC.o] Error 1 rup@ubuntu:~/gui$ make g++ -c gIPC.cpp gIPC.cpp: In member function �void MessageQueue::MsgSnd(Msg)�: gIPC.cpp:18: error: expected primary-expression before �void� gIPC.cpp: In member function �void MessageQueue::MsgRcv(Msg)�: gIPC.cpp:23: error: expected primary-expression before �void� make: * [gIPC.o] Error 1

Apr 15th, 2006, 8:58 AM	#5
InfoGeek Professional Programmer Join Date: Jun 2005 Location: India, The great. Posts: 435 Rep Power: 4	(Toggle Plain Text) SYSTEM CALL: msgsnd(); PROTOTYPE: int msgsnd ( int msqid, struct msgbuf msgp, int msgsz, int msgflg ); SYSTEM CALL: msgsnd(); PROTOTYPE: int msgsnd ( int msqid, struct msgbuf msgp, int msgsz, int msgflg ); msgsnd function expects a struct msgbuf * as the second argument. Why are you passing a void *? __________________ PFO - My daily dose of technology.

Apr 15th, 2006, 9:05 AM	#6
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	(Toggle Plain Text) msgsnd(qid, void(&m), m.GetMsgSize(),0); msgsnd(qid, void(&m), m.GetMsgSize(),0); One doesn't declare a function's parameter type when one calls it, only when one declares or defines it. Did you perhaps mean to cast it? __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Apr 15th, 2006, 8:37 AM	#3
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	As Dawei said, the code snippets given do not give any useful information. It is better to find a SMALL but COMPLETE example that repeatably illustrates your problem (and post it verbatim in code tags). I recommend you read the sticky threads on "How to ask a question" as well .... they give advice on how to ask a question to increase your chances of getting a useful response. The most common reasons the compiler would expect an expression before a function declaration or definition are a missing closing brace i.e. } or a missing semi-colon (or possibly both). But, given that you haven't provided enough information, that is only a stab in the dark.

Apr 15th, 2006, 2:11 PM	#7
rup Newbie Join Date: Jul 2005 Location: India Posts: 14 Rep Power: 0	I picked msgsnd from the book Beginning Linux Programming (Wrox). It has the following prototype: (Toggle Plain Text) int msgsnd(int msqid, const void* msg_ptr, size_t msg_sz, int msgflag); int msgsnd(int msqid, const void* msg_ptr, size_t msg_sz, int msgflag); and is called this way in an example C program in the book: (Toggle Plain Text) msgsnd(msgid, (void)&some_data, MAX_TEXT, 0); msgsnd(msgid, (void)&some_data, MAX_TEXT, 0); where some_data is the structure: (Toggle Plain Text) struct msg{ long int msg_type; char text[MAX_TEXT]; }; struct msg{ long int msg_type; char text[MAX_TEXT]; }; Yes, I meant to cast it.

Apr 15th, 2006, 2:28 PM	#8
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	So, did that clear your error message or not? Inquiring members want to know. It's the fee. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Apr 16th, 2006, 9:26 AM	#9
rup Newbie Join Date: Jul 2005 Location: India Posts: 14 Rep Power: 0	Yes, it cleared my error message. I hade written this: (Toggle Plain Text) msgrcv(qid, void(&m), BUFSIZE, m.GetMsgType(), 0); msgrcv(qid, void(&m), BUFSIZE, m.GetMsgType(), 0); Because in C++ a cast is applied this way : void(variable) I had left it that way. Making it (void*)(&m) solves the problem.

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Programming Forums > Application Development > C++

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