Linking a lib with QT on linux

[Christian Ehrlicher]

@mrjj said in Linking a lib with QT on linux:

So we also need to know the gcc version used to compile the test app.

And the complete error message.

[Keith Harville]

gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.12)

[Keith Harville]

undefined reference to `fwConsole_initConsoleHeader(FW_CONSOLE_HEADER*)'

[Christian Ehrlicher]

Since it's a C library you must make sure that the compiler also interpret your header as C ->

extern "C"
{
#include "fw_console_api.h"
}

Or fix the header so it's not needed for every include of it.

[Keith Harville]

Thank you so much, that fixed it

[mrjj]

@Christian-Ehrlicher
Hi
You are so fast. :)
What did you run on it too see it was a C lib ?
or just be looking in the .h file ?

[Christian Ehrlicher]

@mrjj said in Linking a lib with QT on linux:

What did you run on it too see it was a C lib ?

I got a linker error, looked at the exports and they looked like plain C exports. Then the idea with the wrong symbols was there :)

[mrjj]

@Christian-Ehrlicher
Ok, where did you look at the exports ?
With objdump or ?
Im asking as i want to learn. Since you knew so fast and i was still looking at it :)

[Christian Ehrlicher]

@mrjj said in Linking a lib with QT on linux:

With objdump or ?

Yes, "objdump -T" - take a look at the libfw_console_api.so output and you will notice that they're plain C functions - they are not annotated.

[mrjj]

@Christian-Ehrlicher
Thank you
Its handy to know. goes on my of list of things to try when you get undefined's and
checked path many times :=)

[Keith Harville]

for the header fix, I added in the header and that took care of it

#ifdef __cplusplus
#define FWCONSOLEAPI_DECLSPEC extern  "C"
#else
#define FWCONSOLEAPI_DECLSPEC extern
#endif//__cplusplus

thank you again, you guys are awesome