Compilation and Execution issue

[maven]

Hi,

I am facing a strange issue in C programming. I have a function which is defined in two different libraries. It has difference in number of arguments and functionality.

Now i have taken reference of the function in and used in new program file, which has included both the libraries.
To my surprise it is compiling OK without any warning. As in C we know there can not be name mangling.

While execution it is showing undefined behavior also. Somewhere it calls exact function of same argument and sometimes with different.

Need experts help on this.

[laserlight]

I am not surprised that you did not get compile errors: as long as you included the header with the declaration of the function that you are actually using in a given source file, there is no problem. What surprises me is that you did not get a linking error.

[Adak]

S_cess is waiting for u. Go Ahead, put u there.

Don't we have to spell it successfully, first?

[maven]

You See

[Adak]

See, Sea, and C.

[dmh2000]

if the functions are both in libraries, the linker may pull in the first one it finds and ignore the other one. you would have to examine the link map to see which one you got.

[maven]

Seems interesting! How can see the link map?

[dmh2000]

what tools are you using. if Visual Studio, check the linker option to generate a map file. if GCC, use the 'nm' binutil on the executable to get a link map. in both cases just search for your function name in the map.

[maven]

nm shows me something like:
[2358] | 3974288| 0|FUNC |GLOB |0 |UNDEF |FunctionName. I can not map it with library from which it is!

[Salem]

If you had a file called foo1.c, containing foo(int,int) and you compiled it to lib1.a

Then you had a file called foo2.c, containing foo(char*) and you compiled it to lib2.a

Then doing something like
gcc prog.c -l1 -l2
to link against both libraries will just result in your program seeing foo(int,int), as that was the first library containing a foo() function.

You can pretent to call foo("hello") if you want, but you're still going to get the foo(int,int) function dealing with it (garbage parameters and all).

So long as each instance of foo() originated from a separate compilation unit, then the linker will naturally omit the 2nd instance of foo() in the second library. This is exactly what it is supposed to do.

[maven]

So long as each instance of foo() originated from a separate compilation unit, then the linker will naturally omit the 2nd instance of foo() in the second library. This is exactly what it is supposed to do.

Is there any way to avoid such type of mistakes while compiling or linking??

[anduril462]

A common way is to use a naming prefix for each library, so foo(int,int) in library 1 would be one_foo(int) and foo(char *) in library 2 would be two_foo(char *). That way you don't have two functions with the same name, and you know what library provides that function.

[Adak]

Oh sure! Get organized and cheat, why don't ya? < RoFL >

[maven]

.. Thanks a lot guys! I have Understood the basic problem. using "ldd" i have also traced out the sequence problem.