Bitset in a class

navig8tr (33)
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:
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#include <bitset>

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


This code also compiles without errors:
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#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:
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#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 (519)
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++.
closed account (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:
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#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 (2163)
navig8tr (33)
@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.
Last edited on
navig8tr (33)
I tried this first, but it did not work:
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#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;
}
Last edited on
navig8tr (33)
Although, this works:
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#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 (33)
Okay, so the colon is used for initialization.
closed account (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 (33)
@DTSCode: Nice. Thanks for all the info. I definitely learned something tonight.

Thanks for all the help everyone.
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