How to conditional call a library

thanh_bkhn

Hi all, I have a program that calls magnification.lib in windows 7, windows 8. (I'm calling #include magnification.h) But we know this library doesn't exist in windows XP. How can I ignore this library when opening the application in windows XP?

_Superman_

Create function pointers in a header file for all the magnification APIs that you're going to use. Check the OS version and if Vista or above, call LoadLibrary on Magnification.dll. After this call GetProcAddress on the function to initialize the function pointer. So the header file could look like this -

typedef BOOL (*PFN_MAG_INITIALIZE)(void);

From the main program, you could have a call to some function called InitMagnification. In the InitMagnification function, do the dynamic loading after checking the OS version.

PFN_MAG_INITIALIZE MagInitialize = NULL;

if (osVersion >= "VISTA") // Consider this as pseudo-code
{
HMODULE hmod = LoadLibrary(_T("Magnification.dll"));

MagInitialize = GetProcAddress(hmod, "MagInitialize");

}

In the source where this function is called, do the checking as follows -

if (MagInitialize)
{
MagInitalize();
}

I have omitted error checking, which you have to do.

«_Superman_» _I love work. It gives me something to do between weekends.

_Microsoft MVP (Visual C++) (October 2009 - September 2013)

Polymorphism in C

David Crow

thanh_bkhn wrote:

But we know this library doesn't exist in windows XP.
How can I ignore this library when opening the application in windows XP?

Sounds like you need to read up on implicit vs. explicit linking.

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thanh_bkhn

Thank you very much. After posting this question, I did exactly what you told me to do. Thank you again

thanh_bkhn

Thank you. I performed an explicitly link to my DLL.

chaau

As an alternative, you could use delay load dll. In this case you do not need to change the code you have already written (related to statically linking to the library), all you need to do is just do not call chunk of codes related to magnification at all. Saves you a lot of annoying LoadLibrary/GetProcAddress calls. However, it looks like you have already implemented it. So, just learn about this, so that you could use in future

thanh_bkhn

Thank you for introducing me this. I found this way is more interesting than using LoadLibrary, but I still prefer to the old method, because it helps me to compile the program even on Windows XP