Problem with structure and class

**Bargi** · 09-25-2007

Hi !

Can I declare structure inside class and return pointer to structure.........

like this.......
//xml.h

struct line
{
int width;
int color;
int length;
};

class XML
{

public:
line* read(char* filepath);
int m_width,m_color,m_length;
};

[/code]

Implementation of XML file.........

Code:

line* Xml::read(char* filepath)
{
   line *m_line;
//some operation of parsing file

  m_line->width=m_width;
  m_line->color=m_color;
  m_line->length=m_length;

return line;
}

And this function ic called from fileParser.cpp

Code:

Xml *xml=new Xml();  

line *m_line;

m_line=xml->read(filepath);
cout<<m_line->width<<line_color<<line_length;
}

It is compiling but giving segmentation fault.

Can any body tell me that where is problem........or should I change implementation..

Thanks

**QuantumPete** · 09-25-2007

You need to allocate memory for your line. At the moment m_line just points to random memory that isn't owned by your program. When your program tries to use that memory, the OS complains that you haven't asked for that memory and thus shouldn't be allowed to use it and issues a Segmentation Fault signal, which terminates your program.
Use new to allocate some memory first:

Code:

  line *m_line = new line;
//some operation of parsing file

  m_line->width=m_width

QuantumPete

**ggs** · 09-25-2007

you did allocate memory for m_line with new, right?

m_line = new line;

also your quote shows 'return line', when perhaps it should be 'return m_line'.

but really, you have not pasted enough code or other information to tell why you are getting a seg fault.

unrelated to your programming problems, XML is a very complex format. if you can avoid it, i recommend finding a 3rd party library to parse it for you. or, if you have a choice in the matter, switching to a more lightweight & friendly format, such as s-expressions:

http://en.wikipedia.org/wiki/S-expression
http://people.csail.mit.edu/rivest/sexp.html

the 2nd hosts the source code for a c s-expression parser which i have not used before, but the truth is s-expressions are much better suited to writing your own parser from scratch than XML, which is quite complex and difficult to do properly.

**Bargi** · 09-25-2007

Thanks QuantumPete and ggs for your help...........

Bargi

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