Constructor with parameters makes program crash

[invfo]

Hello.
I wrote a constructor with parameter char * for a class, whose objects are much like strings. And the program aborted, when it came to the part in the main function, where I used this constructor.
What I found unusual is that it aborted not in a typical VisualStudio2008-way, but like a usual windows application (e.g. a video-game).

Here's the code, showing class, constructor and main function:

class FString
{
private:
	char *data;
	char *end;
	int size;
public: 
             FString(char * sample) 
	{
		int i=0; 
		while (*(sample+i)!='\n') // I assume that sample ends with '\n' - that helps me find the end
		{
				i++;
		}
		size=i;
		for (i=0; i<size; i++)
			*(data+i)=*(sample+i);
		end=(data+size-1); 
		
	}
}

void main()
{
             char *test; 
             SCANSTR(test);   //I use this function to input the string
             FString obj(test);  // and here the program crashes
}

So, does anyone have an idea- what's wrong with the constructor? :\

[invfo]

Wow, i've just added

data=new char[size];

after 15th line and now it works, but only if the length of sample is 7 symbols or less.

[Null]

There are quite few things wrong with your code:
1. You don't allocate FString::data so this is the main reason why your program is crashing. Put data=new char[size]; in constructor (EDIT: you already did this)
2. C-style strings always end with '\0' (null) character but you are checking for '\n'

		int i=0; 
		while (*(sample+i)!='\n') // I assume that sample ends with '\n' - that helps me find the end
		{
				i++;
		}

Are you trying to get length of the string? There is an easer way to get length of a string with strlen() function:
int length_of_string=strlen(sample);

		for (i=0; i<size; i++)
			*(data+i)=*(sample+i);

You can use strcpy to copy strings: http://www.cplusplus.com/strcpy

3. You didn't put a semicolon in line 21 so your code shouldn't compile.
4. Line 23: You should use int main() instead of void main()

[invfo]

Thanks a lot for the answer. Semicolon in 21 was just a typo. I tried your advices from 2)
At first I rewrote my code like this:

	FString(char * sample)
	{
		int i=0; 
		size=strlen(sample);
		data=new char[size];
		strcpy (data,sample);
		end=(data+size-1); 		
	}

and then I tried this:

	FString(char * sample) 
	{
		int i=0; 
		size=strlen(sample);
		data=new char[size];
		for (i=0; i<size; i++)
			*(data+i)=*(sample+i);
		end=(data+size-1); 		
	}

When i run both of these variants, the program still crashes, if strlen(sample) > 7

[Null]

Maybe I'm missing something. One more thing, can you post your SCANSTR function?

[invfo]

Sure. *My code's so ugly*

void SCANSTR(char *& test, int & len)
{
	char a;
	int check=1;
	test=new char[];	
	int i=0; 
	do
	{	
		scanf("%c", test+i);		
		if (*(test+i)=='\n') 
		{
			check=0;			
		}
		i++;
	}
	while (check!=0);
	len=i-1;
}

I was ashamed of my SCANSTR so I rewrote it to what you see in this post.
Now program runs fine, except when strlen(sample)==8.
One more thing, that changed after I used string-functions: I found some garbage in *data, when printing it.
(edit: for some reason, size, defined as
size=strlen(sample);
equals 14. Which may be because I define sample as
sample=new char[]
and not as
sample=new char[certain_size] )

[Null]

Your don't need SCANSTR function:

// your main function
int main()
{
             std::string test;
             getline(cin,test);
             FString obj(test.c_str());  
}

change FString(char * sample) to FString(const char * sample)
And don't forget to #include <string>

[invfo]

Thanks a lot. That works perfect, but I'd like to ask some questions.

1) Why is the argument of constructor "test.c_str()" and not just "test" ?
(edit: I`ve just read about c_str and as I understood, test.c_str ~ * test (if test would be char)
2) Is string variable the same, as char * ?
edit: The answer is probably 'no', so is there a way do something like this?

  std::string test;
  getline(cin,test);
 char * st = &test;

one more edit: I did it like

 std::string test;
 getline(cin,test);
 char *a;
 a = new char [test.size()];
 strcpy (a, test.c_str());
 FString obj(a); 

So, everything's clear now (the problem seem to be with SCANSTR function)

[Null]

2) No, they are very different. string is a class designed for strig manipulation while char * is a pointer to some memory location which contains your string (aka C-Style strings)
You can find out more about C-style strings here: http://www.cplusplus.com/doc/tutorial/ntcs/
and about strong class here http://www.cplusplus.com/reference/string/string/

1) .c_str() returns C-Style string equivalent of std::string
http://www.cplusplus.com/reference/string/string/c_str/

EDIT You can delete line 4 from your second example - it does nothing.

[invfo]

That line was just another typo.
String seems to be very useful class.
Thank you one more time. Finally I'm done with this nasty constructor.