Bitset in a class

[navig8tr]

I've declared and initialized a bitset in main with no problems, however when I use the same syntax in a class I get compiler errors.

The following code compiles with no errors:

#include <bitset>

int main(int argc, char** argv) 
{
	const std::bitset<4> DIVISOR (std::string("0011"));
	return 0;
}

This code also compiles without errors:

#include <bitset>
#include <string>

class CRC
{
	private:
		const std::bitset<4> DIVISOR; // (std::string("0011"));
}
;

int main(int argc, char** argv) 
{
	CRC myCRC;
	return 0;
}

However, this code produces compilation errors:

#include <bitset>
#include <string>

class CRC
{
	private:
		const std::bitset<4> DIVISOR (std::string("0011"));
}
;

int main(int argc, char** argv) 
{
	CRC myCRC;
	return 0;
}

The error says, "[Error] expected ')' before string constant".

Why would the same syntax work in main but not in a class?
I've tried getting rid of the private and const keywords, but the error persists. Any suggestions would be greatly appreciated.

[GRex2595]

It'll work if you set it in the default constructor. If I remember correctly, you can't set or instantiate class variables in C++.

[Dy7SLyTq]

It'll work if you set it in the default constructor.

that doesnt make any sense. a default constructor is one the compiler generates if you dont have a constructor, so you can't place code in it. as to op: what you need to do is this:

#include <bitset>
#include <string>

class CRC
{
	private:
		const std::bitset<4> DIVISOR;

	public:
		CRC() : DIVISOR(std::string("0011")) {}
}
;

int main(int argc, char** argv) 
{
	CRC myCRC;
	return 0;
}

in c++11 you can initialize class members at declaration with the = operator, but you can't "call" a constructor like that

[naraku9333]

@DTSCode http://en.wikipedia.org/wiki/Default_constructor

[navig8tr]

@DTSCode: Your code worked great. Thanks a lot. As to the syntax you used: is that a shorthand way of defining the constructor?

I've actually heard people call a constructor without parameters a default constructor--I assumed this is what GRex was referring to.

[navig8tr]

I tried this first, but it did not work:

#include <bitset>
#include <string>

class CRC
{
	private:
		const std::bitset<4> DIVISOR;

	public:
		CRC();
}
;

CRC::CRC()
{
	  DIVISOR (std::string("0011"));
}

int main(int argc, char** argv) 
{
	CRC myCRC;
	return 0;
}

[navig8tr]

Although, this works:

#include <bitset>
#include <string>

class CRC
{
	private:
		const std::bitset<4> DIVISOR;
	public:
		CRC();
}
;

CRC::CRC() : DIVISOR (std::string("0011"))
{
	
}

int main(int argc, char** argv) 
{
	CRC myCRC;
	return 0;
}

[navig8tr]

Okay, so the colon is used for initialization.

[Dy7SLyTq]

@naraku&GRex: my bad. i wasnt aware c++ had its own meaning. i thought it was the oop def

@op: yes. it calls the the constructor at declaration. the reason this http://www.cplusplus.com/forum/beginner/113905/#msg622066 doesnt work is because constructors can only be called upon the declaration of the variable, not willy nilly. the reason why http://www.cplusplus.com/forum/beginner/113905/#msg622067 works is because you essentially wrote the same thing i did, except you did it outside of the class, which is useful when you have large methods. there might be other performance issues, but thats the major one imo

[navig8tr]

@DTSCode: Nice. Thanks for all the info. I definitely learned something tonight.

Thanks for all the help everyone.