I created a c .so object, and can link successfully, now I want to make it for c++

morty346 · 06-11-2009, 08:30 AM

I created a c .so object, and can link successfully, I now need it to work with a cpp, so I converted my .so into a cpp, I added extern "C" to all of my functions that are needing exported, and it seems to be fine, except when its time to link it with a .cpp main

I can compile it with a .c main file, I do get warnings, but it does work

When I switch my main to a cpp the warnings seem to turn into errors

Warning in C:
implicit declaration of "Function"

Error in C++:
"Function" was not declared in scope

To Compile the c or cpp i use

Code:

$ gcc -o client client.cpp -L. -lprint
or
$ gcc -o client client.c -L. -lprint

I have followed this tutorial almost verbatim
http://www.ibm.com/developerworks/library/l-shobj/

Uncle_Theodore · 06-11-2009, 08:34 AM

It's hard to say anything without reading your code, but with C++ it's a little bit trickier. You might want to take a look at this tutorial.
http://tldp.org/HOWTO/C++-dlopen/

paulsm4 · 06-11-2009, 09:20 AM

Hi -

Quote:

Warning in C:
implicit declaration of "Function"

Error in C++:
"Function" was not declared in scope

This is a compiler error: you need to *declare* a function before you use it. For example:

Quote:

myheader.h =>

Code:

#ifdef __cplusplus
  extern "C" {
#endif

int MyFunction (int x, int y);

#ifdef __cplusplus
  }
#endif

myprogram.c =>

Code:

   ...
   int i = MyFunction (2, 3);

In other words:
1. Be sure to declare your functions before you use them (e.g. with a "function prototype")
2. Ideally, you should be able to put all your prototypes in a header file
3. Be sure to use "extern C" in your prototype declaration.

This link explains further:
http://www.parashift.com/c++-faq-lit...c-and-cpp.html

'Hope that helps .. PSM

morty346 · 06-11-2009, 10:18 AM

Quote:

Originally Posted by paulsm4

Hi -

This is a compiler error: you need to *declare* a function before you use it. For example:

In other words:
1. Be sure to declare your functions before you use them (e.g. with a "function prototype")
2. Ideally, you should be able to put all your prototypes in a header file
3. Be sure to use "extern C" in your prototype declaration.

This link explains further:
http://www.parashift.com/c++-faq-lit...c-and-cpp.html

'Hope that helps .. PSM

Thank you
however, we are using a .h, and everything has extern "C" infront of it, both declaration and definition

paulsm4 · 06-11-2009, 10:24 AM

Hi -

1. If you're getting 'implicit declaration of "Function"', then "Function()" doesn't have a prototype - or at least the prototype isn't visible to the guy who needs it.

2. If you have an 'extern "C" {}' for your declaration ... then you don't need it for the definition.

So check again: you're probably missing something very, very simple.

PS:
Try hedging your bets, and compile with "g++" instead of "gcc". Can't hurt; might help. At least help track down the actual problem...