Re: Cannot call read function!
On 3 Ott, 17:34, davee <da...@nomail.com> wrote:
Francesco S. Carta wrote:
On 3 Ott, 17:05, davee <da...@nomail.com> wrote:
I am trying to use the code posted here:
http://www.senzee5.com/2008/02/java-style-properties-files-in-c.html
I use it like this:
#include "propertyutil.h"
int main(){
PropertyUtil properties;
typedef PropertyUtil::PropertyMapT MapType;
MapType bob;
properties.read(config_path.c_str(), bob);
return 0;
}
but I get the error:
main.cpp:(.text+0xc29): undefined reference to `PropertyUtil::read(char
const*, std::map<std::basic_string<char, std::char_traits<char>,
std::allocator<char> >, std::basic_string<char, std::char_traits<char>,
std::allocator<char> >, std::less<std::basic_string<char,
std::char_traits<char>, std::allocator<char> > >,
std::allocator<std::pair<std::basic_string<char, std::char_traits<char>,
std::allocator<char> > const, std::basic_string<char,
std::char_traits<char>, std::allocator<char> > > > >&)'
'read' is:
class PropertyUtil {
enum { DEBUG = 0 };
public:
typedef std::map<std::string, std::string> PropertyMapT;
typedef PropertyMapT::value_type value_type;
typedef PropertyMapT::iterator iterator;
static void read(const char *filename, PropertyMapT &map);
..
..
What am I doing wrong here?
An error telling "undefined reference to [whatever]" comes from the
linker. It means that no available compilation unit defined that thing
- it is just _declared_, in that header.
In this very case, find out what library you need, download it and add
it to your linker references.
When you get the same kind of errors with your very names, that would
mean that you forgot to define those names (that is, you just declared
them, as it happened above).
Have good time,
Francesco
--
Francesco S. Carta, hobbyist
http://fscode.altervista.org
Ah I just needed to add:
#include "propertyutil.cpp"
in the end of the propertyutil.h file, seems a bit wierd though. But
since I am using it in a "header only" library this might be the
explanation.
If you _really_ added
-------
#include "propertyutil.cpp"
-------
to the _end_ of "propertyutil.h", you must have removed
-------
#include "propertyutil.h"
-------
from "propertyutil.cpp"
If you didn't remove that line, you must have had your preprocessor
chocking on inclusion's nesting level - otherwise, you didn't add it
at the end of the file but before of "#endif".
But apart of that, no, you shouldn't really include implementation
files into headers that way.
A header-only library is plainly that: a library that consists only of
headers.
That propertyutil thing isn't header-only at all.
You should either add that cpp file to your project (assuming you're
working within an IDE) otherwise you should explicitly pass it to your
compiler (assuming you're working in a shell/console).
Another way consists of making a separate library out of it, but maybe
you want to postpone a bit these arguments.
To include an implementation file in a header file - assuming you
_really_ need to do so, which isn't this case at all - you need to do
it conscientiously, otherwise you can end up having multiple
definitions and your program won't compile.
Consider this case:
Content of foo_header.h:
-------
#ifndef FOO_HEADER_H
#define FOO_HEADER_H
void foo(); // declaration
#endif
// inclusion after the #endif
#include "foo_implementation.cpp"
-------
Content of module1.cpp
-------
#include "foo_header.h"
// use foo()
-------
Content of module2.cpp
-------
#include "foo_header.h"
// use foo()
-------
And apart, not compiled,
inside of foo_implementation.cpp:
-------
void foo() {
// definition
}
-------
Given all the above, you'll end up with _one_ declaration of foo and
with _two_ definitions of the same, and your compilation will fail.
The right way to include it is like this:
-------
#ifndef FOO_HEADER_H
#define FOO_HEADER_H
void foo();
// inclusion _before_ the #endif
#include "foo_implementation.cpp"
#endif
-------
Such inclusion is really needed if and only if:
- foo is a template
AND
- your compiler doesn't support the "export" keyword
In all the other cases, including a non-header file within another
file is just the wrong way of doing things.
Hope this wasn't too messy of an explanation. Feel free to ask if you
need, although you can find tons of informations hanging around, in
the CLC++ FAQ for starters.
--
Francesco S. Carta, hobbyist
http://fscode.altervista.org