class name not found in same namespace?

xucaen · 02-23-2018, 10:32 PM

I have a weird situation which I have not run into before today. Before today I primarily work in windows with Visual Studio, so something may have changed in the c++ standard that I don't under stand (and I don't even know what to search for). The code below is an example of what I am seeing. My code compiles in Visual Studio but not gcc.

I have two classes:

class_a.h

Code:

namespace AAA
{
    namespace BBB
    {
        class MyTest
        {
             
        }
    }
}

class_b.h

Code:

#include "class_a.h"
namespace AAA
{
    namespace BBB
    {
        class AnotherClass
        {
             virtual MyTest getMyTest() = 0;//error: ‘MyTest’ has not been declared

        }
    }
}

In this example, I get a compiler error "‘MyTest’ has not been declared".
I can't see what I am doing wrong. It's probably a compiler parameter I need, but then I don't even know what this is.. is this some kind of scope issue? or are nested namespaces only allowed under certain circumstances? Or maybe it has something to do with virtual? I have no idea. any help is appreciated.

BW-userx · 02-23-2018, 10:41 PM

this is what I am getting.

Code:

$ g++ main.cpp
In file included from class_b.h:1:0,
                 from main.cpp:3:
class_a.h:5:15: error: redefinition of 'class AAA::BBB::MyTest'
         class MyTest
               ^~~~~~
In file included from main.cpp:2:0:
class_a.h:5:15: note: previous definition of 'class AAA::BBB::MyTest'
         class MyTest
               ^~~~~~

main

Code:

#include <iostream>
#include "class_a.h"
#include "class_b.h"

int main() {

	
}

with direct copies of your code with added ; at end of class declaration.

grail · 02-24-2018, 01:13 AM

Seemed to work without error for me and all I changed was adding a return in main and not including class_a.h twice.
So main now looked like:

Code:

#include <iostream>
#include "class_b.h"

int main() {

	return 0;
	
}

All other files as is and compiled using same command as BW-userx.

Which also begs the question on what was missed in original question, how did you try to compile your code?

xucaen · 02-24-2018, 08:05 AM

I apologize to everyone reading this. I know better than to post a technical question late at night without including all the technical details, and yet I did it anyway. I am working on an accurate example now to recreate the issue. I will post more later.

BW-userx · 02-24-2018, 08:10 AM

Quote:

Originally Posted by xucaen

I apologize to everyone reading this. I know better than to post a technical question late at night without including all the technical details, and yet I did it anyway. I am working on an accurate example now to recreate the issue. I will post more later.

if you cannot (re)create it then why create it. if it is gone then let it be gone and move on with it.that's what I say. no harm no foul.

xucaen · 02-24-2018, 08:43 AM

OK, here is an accurate example that recreates my issue exactly. I have a typedef which has no semicolon. I'm not sure when they started requiring that typedefs have semicolons but I have never used semicolons with typedefs before, and my original code compiles in Visual Studio (I did not specifically compile this example in Visual Studio, I only mean to say that I have similar source code that has typedefs with no semicolons that does compile in VS)

So, is there a way to tell g++ to allow typedefs with no semicolons? For now, I'll just put in the semicolon and be done with it.

MyTest.h

Code:

#pragma once

typedef int CCCC

namespace AAAA
{
	namespace BBBB 
	{
		class MyTest
		{
		public:
			void test();
		};

	}
}

MyTest.cpp

Code:

#include "MyTest.h"
namespace AAAA
{
	namespace BBBB 
	{

		void MyTest::test()
		{
		}

	}
}

makefile

Code:

CC = g++
CFLAGS = -g -Wall -ansi  
COBJ = -c
CEXE = -o $@
SRC=MyTest.cpp
HDR=MyTest.h  

all:	mytest.o

mytest.o: $(SRC) $(HDR)
	$(CC) $(CFLAGS) $(COBJ) $(SRC)

run make.

Compiler output with typedef:

Quote:

g++ -g -Wall -ansi -c MyTest.cpp
In file included from MyTest.cpp:1:0:
MyTest.h:5:1: error: expected initializer before ‘namespace’
namespace AAAA
^~~~~~~~~
MyTest.cpp:7:8: error: ‘MyTest’ has not been declared
void MyTest::test()
^~~~~~
makefile:11: recipe for target 'mytest.o' failed
make: *** [mytest.o] Error 1

Compiler output with no typedef:

Quote:

g++ -g -Wall -ansi -c MyTest.cpp

BW-userx · 02-24-2018, 09:09 AM

adding that semi colon

Code:

$ make
g++ -g -Wall -ansi   -c MyTest.cpp
userx@slackwhere101:~/testdir
$ ls
Makefile  MyTest.cpp  MyTest.h  MyTest.o

I'd think that you would/might have to tell in your makefile what version specs of c++ to use to have it use the rules that you stated did not require a semi colon at the end of a typedef like but not necessarily this one

Code:

-std=c++11

NevemTeve · 02-24-2018, 09:19 AM

I think most of the characters in the source code are important, there no is point leaving out some of them.

ntubski · 02-24-2018, 11:50 AM

Quote:

Originally Posted by xucaen

I have a typedef which has no semicolon. I'm not sure when they started requiring that typedefs have semicolons but I have never used semicolons with typedefs before, and my original code compiles in Visual Studio (I did not specifically compile this example in Visual Studio, I only mean to say that I have similar source code that has typedefs with no semicolons that does compile in VS)

AFAIK, C (and C++) always required a semicolon at the end of a typedef statement. Perhaps you're confusing it with a "fake typedef" via the proprocessor? E.g.

Code:

#define CCCC int
// almost the same as
typedef int CCCC;

xucaen · 02-25-2018, 09:22 AM

No, I copied the code from my Windows PC. The code builds and runs perfectly well in Windows 10 without the semicolon on the typedef. Give it a try in visual studio.

pan64 · 02-25-2018, 09:29 AM

that is a question: if it works with ; on linux. I do not really care about Visual Studio. Different compiler - different syntax checker. By the way which version of gcc/g++ did you try?

xucaen · 02-25-2018, 09:42 AM

I'm using whatever comes stock with Ubuntu 17.1.

pan64 · 02-25-2018, 09:51 AM

gcc --version

BW-userx · 02-25-2018, 02:15 PM

Quote:

Originally Posted by xucaen

No, I copied the code from my Windows PC. The code builds and runs perfectly well in Windows 10 without the semicolon on the typedef. Give it a try in visual studio.

yeahhhh do you see what is going on here? Windows is causing you to develop a habit of not being compatible with anything other than Windows habits. try it the way it works in Linux in your visual code whatever thingy and see if it accepts the typedef with a semicolon.

xucaen · 02-25-2018, 02:27 PM

Quote:

Originally Posted by BW-userx

yeahhhh do you see what is going on here? Windows is causing you to develop a habit of not being compatible with anything other than Windows habits. try it the way it works in Linux in your visual code whatever thingy and see if it accepts the typedef with a semicolon.

That's what I said to my wife when I realized what the problem was. Lol. Microsift makes programmers lazy.