Why Am I Getting an "Implicit Declaration of Function 'Ndo_Get_Stats' " Error

why am I getting an implicit declaration of function 'ndo_get_stats' error?

ndo_get_stats is a net_device_ops function pointer. You have to call it through the netdev_ops field of your net_device.

Something like this would work:

stats = dev->netdev_ops->ndo_get_stats(dev);

net_device get_stats function, how to use?

This is not a function. Its the declaration of a function pointer get_stats which points to a function which receives a pointer to the structure net_device and returns a pointer to a structure of type net_device_stats

Here is one use case

struct net_device *dev;
struct net_device_stats *device;

device = get_stats(dev);

EDIT From your comments, I see you are using an older version of the kernel. IN later kernels , structure net_device still resides in linux/netdevice.h but there's no get_stats function pointer. Its changed into ndo_get_stats and it is now under another structure net_device_ops

So start using these new function pointers.

C warning: implicit declaration of function

For a start, I don't think it's a good idea to be giving common.h to the compiler in the makefile:

@$(CC) $(C_FLAGS) -c sgbd_server.c common.h

This would be better as just:

@$(CC) $(C_FLAGS) -c sgbd_server.c

Header files are usually incorporated with just an #include. You appear to be telling the compiler to try and compile common.h as a standalone C file. That's one difference between the client and server compile commands and you should fix it.

The only other thing I can suggest is that you may not be getting the header files you think you're getting. Start by putting the line:

#error Urk! in common.h

at the top of your common.h and ensure the build fails there.

If not, then that file is coming from somewhere else. You may also want to do the same thing with your sgbd_server.h file as well.

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Based on your edit:

I found some .ghc files sitting in my source folder. Since they are not cleaned by make clean, I deleted manually those files. Guess what? No warning. What are those files and why are they created?

These are, assuming ghc was a typo and you meant gch, pre-compiled headers generated by gcc, at least in part to speed up the compilation process. Rather than having to process a header file many times during a build (once per source file that includes it), pre-compiling it once and using the pre-compiled version is a lot more efficient.

I think this was most likely cause by the fact that you included common.h on your compiler command line when you did the server. By default, header files given directly to gcc will be turned into pre-compiled header files and used in preference after that point. To test this, I created a qq.h file and executed gcc qq.h and out popped qq.h.gch.

It's quite likely, given that deleting them solved your problem, that these files were somehow causing your issues (be that the presence of pre-compiled headers older than the real headers or something else entirely). There's a good chance that your compile line:

@$(CC) $(C_FLAGS) -c sgbd_server.c common.h

would first compile the server program, including the old precompiled header, then make a new precompiled header out of the newer header file.

That's probably why a change to common.h had no (immediate) effect. You would have to make ; touch common.h ; make to ensure the newer pre-compiled header file was used in the server program.

Whether you want to track it back to the root cause and get a proper explanation is a matter of taste - there's a school of thought that you should sometimes just record how you fixed it and not worry too much, lest you become entangled in the very nature of reality itself.

Not me of course, I'm the personality type that will attempt to track my problems back to the individual sub-atomic particle that caused it, but sometimes pragmatism requires me to let it go :-)

Implicit declaration of function (static library)

Because static libraries are only read by the linker at the linking stage (and the static library doesn't contain its functions signatures anyway). The compiler needs to know what this function is at the compile stage. So you need to include the header file providing your function's signature.

implicit declaration of function ‘write’; did you mean ‘fwrite’?

To access the Posix low level file interface such as open, read, write and close, you should include <unistd.h>.

Note however that your program does not seem to require such low level interface, you might consider creating your output file using standard streams declared in <stdio.h>, using fopen, fputs or fprintf and fclose.

warning : Implicit declaration error

But i have defined it in bloc.c.

You may have defined it, but you also have to declare it

Declaring said function in bloc.h should fix it.

Implicit declaration of function ‘mknod’ but I have the headers included

As you can see that for declaration of mknod() function to stay after preprocessing stage, one of three macros (__USE_MISC, __USE_BSD, __USE_XOPEN_EXTENDED) should be defined. Otherwise, declaration of mknod() will be removed during preprocessing stage.

#if defined __USE_MISC || defined __USE_BSD || defined __USE_XOPEN_EXTENDED
extern int mknod (const char *__path, __mode_t __mode, __dev_t __dev)
 __THROW __nonnull ((1));

You can use compiler options: -std=gnu99 -D_GNU_SOURCE or you can define these macros on your own and place them above header file inclusion.

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