C to C++ conversion

racerday182 · 12-03-2008, 02:15 AM

Hey everybody,
I was having trouble completing my last assignment which required me to redesign a C program into a C++ program using classes and objects.
So far my Cpp code looks like this:
insert

Code:

class Ciphertext{
public:
	void output_ciphertext_screen(struct key_element key[26], FILE * fp);
};

void Ciphertext::output_ciphertext_screen(struct key_element key[26], FILE * fp)
{
	int i;
	fprintf(fp,"\n");
	fprintf(fp,"Encoded : ");
	for(i=0;i<26;i++)
		fprintf(fp,"%c ",key[i].enc);
	fprintf(fp,"\n");
	fprintf(fp,"Decoded : ");
	for(i=0;i<26;i++)
		if(key[i].man_flag == 0)
			fprintf(fp,"%c ",key[i].dec);
		else
			if(fp==stdout)
				printf("%c ",toupper(key[i].dec));
			else
				fprintf(fp,"%c ",key[i].dec);
	fprintf(fp,"\n\n");

}

int main()
{
	
		output_ciphertext_screen print(key, stdout);
}

This code is supposed to take a ciphertext line by line from a file and output it onto the screen using C++. Basically, all I did was take the function I had earlier that is supposed to perform this operation and copied it into the object above. But, after compiling, I am getting errors saying:
error C2065: 'output_ciphertext_screen' : undeclared identifier.
I am new to C++ and am trying to get a better grasp of it so if you could point me in the right direction by showing me where my code is wrong or just giving me some tips, I should be able to figure out the rest of the program.
Thanks in advance,
Andy

**laserlight** · 12-03-2008, 02:21 AM

You need to create a Ciphertext object and call output_ciphertext_screen using it. Of course the key variable also should be defined.

Code:

int main()
{
    Ciphertext cipher_text;
    cipher_text.output_ciphertext_screen(key, stdout);
}

Incidentally, in C++ we often use the C++ I/O stream library instead of C I/O, so we would use std::cout instead of stdout and std::ostream (or std::istream) instead of FILE*.

racerday182 · 12-03-2008, 11:10 AM

Arite, tried that and it gets rid of the errors, but what do I need to do to actually get the program to print out the ciphertext, do i need to define some private members within my class?
Oh and as for using C++ I/O we are not required to do that, but if that makes the program easier I might go back and change that.

Thanks again

**laserlight** · 12-03-2008, 11:16 AM

Quote:

Originally Posted by racerday182

what do I need to do to actually get the program to print out the ciphertext, do i need to define some private members within my class?

That would be implementation detail. The output_ciphertext_screen() member function is sufficient.

Quote:

Originally Posted by racerday182

Oh and as for using C++ I/O we are not required to do that, but if that makes the program easier I might go back and change that.

One way would be to overload operator<< for std::ostream such that you can write:

Code:

std::cout << cipher_text;

and the ciphertext would be printed to std::cout (i.e., the C++ I/O equivalent of stdout).
However, in this case it is mainly just syntactic sugar over output_ciphertext_screen().

C_ntua · 12-03-2008, 11:21 AM

Well, I guess you would define a private member called key inside Ciphertext. But you don't NEED to do that. You could just do:

Code:

int main()
{
   Ciphertext ct;
   key_element myKey[SIZE];
   //fill myKey
   ct.output_ciphertext_screen print(myKey, stdout);  
}

But it makes more sense to do:

Code:

int main()
{
   Ciphertext ct;
   ct.Insert(...); //will get a key and store it insided a private key_element of Ciphertext
   output_ciphertext_screen print(myKey, stdout);  
}

Were insert would be a faction you have to make that either just takes a key_element and stores it either prompts for it and/or read it from a file

The first code is bad. It would be OK if you declared output_ciphertext_screen static (and/or Ciphertext itself?) and do:

Code:

int main()
{
   key_element myKey[SIZE];
   //fill myKey
   Ciphertext::output_ciphertext_screen print(myKey, stdout);  
}

**laserlight** · 12-03-2008, 06:20 PM

Quote:

Originally Posted by C_ntua

Well, I guess you would define a private member called key inside Ciphertext. But you don't NEED to do that. You could just do:

I think that the important question to ask is: what does the Ciphertext class model?

Admittedly, I did not look very closely into the given code, but now I see that the Ciphertext class seems to be doing more than it should. The output_ciphertext_screen() is misleading because it does not just output ciphertext, but outputs plaintext as well (and not necessarily to the "screen").

racerday182, think of what is the purpose of the Ciphertext class. Think of the classes that would work with it. Do you have a hierarchy of cryptographic algorithm classes, for example? If you do things the "C++ way" as overload operator<< as I suggested, then that should really just print the ciphertext, not the plaintext. Would it print the ciphertext by applying an encryption mode? If so, what about an initialisation vector? Should a key even come into the picture? Perhaps the key also comes into play for the function that generates the ciphertext, hence the ciphertext itself has no notion of a key.

Keep in mind that a class should model one thing and model it well, and a function should do one thing and do it well.

Quote:

Originally Posted by C_ntua

The first code is bad. It would be OK if you declared output_ciphertext_screen static (and/or Ciphertext itself?) and do:

That is probably even worse: why should that member function be static?

12-03-2008, 02:15 AM	#1
racerday182 Registered User Join Date: Nov 2008 Posts: 11	C to C++ conversion Hey everybody, I was having trouble completing my last assignment which required me to redesign a C program into a C++ program using classes and objects. So far my Cpp code looks like this: insert Code: class Ciphertext{ public: void output_ciphertext_screen(struct key_element key[26], FILE * fp); }; void Ciphertext::output_ciphertext_screen(struct key_element key[26], FILE * fp) { int i; fprintf(fp,"\n"); fprintf(fp,"Encoded : "); for(i=0;i<26;i++) fprintf(fp,"%c ",key[i].enc); fprintf(fp,"\n"); fprintf(fp,"Decoded : "); for(i=0;i<26;i++) if(key[i].man_flag == 0) fprintf(fp,"%c ",key[i].dec); else if(fp==stdout) printf("%c ",toupper(key[i].dec)); else fprintf(fp,"%c ",key[i].dec); fprintf(fp,"\n\n"); } int main() { output_ciphertext_screen print(key, stdout); } This code is supposed to take a ciphertext line by line from a file and output it onto the screen using C++. Basically, all I did was take the function I had earlier that is supposed to perform this operation and copied it into the object above. But, after compiling, I am getting errors saying: error C2065: 'output_ciphertext_screen' : undeclared identifier. I am new to C++ and am trying to get a better grasp of it so if you could point me in the right direction by showing me where my code is wrong or just giving me some tips, I should be able to figure out the rest of the program. Thanks in advance, Andy
racerday182 is offline

12-03-2008, 02:21 AM	#2
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 11,319	You need to create a Ciphertext object and call output_ciphertext_screen using it. Of course the key variable also should be defined. Code: int main() { Ciphertext cipher_text; cipher_text.output_ciphertext_screen(key, stdout); } Incidentally, in C++ we often use the C++ I/O stream library instead of C I/O, so we would use std::cout instead of stdout and std::ostream (or std::istream) instead of FILE*. __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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12-03-2008, 11:10 AM	#3
racerday182 Registered User Join Date: Nov 2008 Posts: 11	Next Step Arite, tried that and it gets rid of the errors, but what do I need to do to actually get the program to print out the ciphertext, do i need to define some private members within my class? Oh and as for using C++ I/O we are not required to do that, but if that makes the program easier I might go back and change that. Thanks again
racerday182 is offline

12-03-2008, 11:21 AM	#5
C_ntua Registered User Join Date: Jun 2008 Posts: 1,276	Well, I guess you would define a private member called key inside Ciphertext. But you don't NEED to do that. You could just do: Code: int main() { Ciphertext ct; key_element myKey[SIZE]; //fill myKey ct.output_ciphertext_screen print(myKey, stdout); } But it makes more sense to do: Code: int main() { Ciphertext ct; ct.Insert(...); //will get a key and store it insided a private key_element of Ciphertext output_ciphertext_screen print(myKey, stdout); } Were insert would be a faction you have to make that either just takes a key_element and stores it either prompts for it and/or read it from a file The first code is bad. It would be OK if you declared output_ciphertext_screen static (and/or Ciphertext itself?) and do: Code: int main() { key_element myKey[SIZE]; //fill myKey Ciphertext::output_ciphertext_screen print(myKey, stdout); }
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