Programming Forums > Application Development > C++

rup · Mar 15th, 2006, 1:59 AM

I have transformed a single-file C code to this single cpp file, using oop. The c program works fine. I have included the same header files. Then why am i getting this error? (I program in Linux)

the cpp file name:
grp.cpp

compiled this way at the command line:
g++ -o grp grp.cpp

I get this error message:
In constructor �FB_Draw::FB_Draw()�:
grp.cpp:26: error: �ioctl� was not declared in this scope

Here is s implified form of my code:

(Toggle Plain Text)

//grp.cpp

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>

class FB_Draw{	
        public:
	
        //constructor
	FB_Draw(){
		//....
		ioctl(..);
	}

	void FB_DrawPixel(..){
		//...
	}
		
	//other functions
};

int main()
{
	FB_Draw fb;
	fb.FB_DrawPixel(10,10);
	return 0;
}

The Dark · Mar 15th, 2006, 2:47 AM

According to the ioctl man page, you need to include <sys/ioctl.h>.
A C compiler will allow functions to be used without being declared or defined first (it makes some assumptions about the return type and parameters), but a C++ compiler won't allow that.

rup · Mar 15th, 2006, 10:55 AM

Thank you, I included <sys/ioctl.h> and now the program is working fine.

grumpy · Mar 16th, 2006, 6:38 AM

As The-Dark said, the reason it would compile in C is that C does not require a function declaration (i.e. a prototype) to be able to call a function. At the first call of a function, if there has been no prototype, it will assume the function returns int and takes any number of arguments (and the type of any arguments passed will not be checked).

A C++ compiler will reject the same code because it enforces types of argument and return type of a function. It will therefore reject a call to a function that is called with no previous declaration.

bl00dninja · Mar 18th, 2006, 1:56 AM

did not know that!

Mar 15th, 2006, 1:59 AM	#1
rup Newbie Join Date: Jul 2005 Location: India Posts: 14 Rep Power: 0	Changed a C code to a C++ oo code, and found this error. I have transformed a single-file C code to this single cpp file, using oop. The c program works fine. I have included the same header files. Then why am i getting this error? (I program in Linux) the cpp file name: grp.cpp compiled this way at the command line: g++ -o grp grp.cpp I get this error message: In constructor �FB_Draw::FB_Draw()�: grp.cpp:26: error: �ioctl� was not declared in this scope Here is s implified form of my code: (Toggle Plain Text) //grp.cpp #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <fcntl.h> #include <linux/fb.h> #include <sys/mman.h> class FB_Draw{ public: //constructor FB_Draw(){ //.... ioctl(..); } void FB_DrawPixel(..){ //... } //other functions }; int main() { FB_Draw fb; fb.FB_DrawPixel(10,10); return 0; } //grp.cpp #include <stdlib.h> #include <unistd.h> #include <stdio.h> #include <fcntl.h> #include <linux/fb.h> #include <sys/mman.h> class FB_Draw{ public: //constructor FB_Draw(){ //.... ioctl(..); } void FB_DrawPixel(..){ //... } //other functions }; int main() { FB_Draw fb; fb.FB_DrawPixel(10,10); return 0; }

Mar 18th, 2006, 1:56 AM	#5
bl00dninja Programming Guru Join Date: Oct 2004 Location: namespace std Posts: 1,246 Rep Power: 6	did not know that! __________________ i put on my robe and wizard hat... Have you ever heard of Plato, Aristotle, Socrates?...Morons.

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Mar 15th, 2006, 2:47 AM	#2
The Dark Expert Programmer Join Date: Jun 2005 Posts: 894 Rep Power: 4	According to the ioctl man page, you need to include <sys/ioctl.h>. A C compiler will allow functions to be used without being declared or defined first (it makes some assumptions about the return type and parameters), but a C++ compiler won't allow that.

Mar 15th, 2006, 10:55 AM	#3
rup Newbie Join Date: Jul 2005 Location: India Posts: 14 Rep Power: 0	Thank you, I included <sys/ioctl.h> and now the program is working fine.

Mar 16th, 2006, 6:38 AM	#4
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	As The-Dark said, the reason it would compile in C is that C does not require a function declaration (i.e. a prototype) to be able to call a function. At the first call of a function, if there has been no prototype, it will assume the function returns int and takes any number of arguments (and the type of any arguments passed will not be checked). A C++ compiler will reject the same code because it enforces types of argument and return type of a function. It will therefore reject a call to a function that is called with no previous declaration.

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Programming Forums > Application Development > C++

Changed a C code to a C++ oo code, and found this error.