Little doubt regarding #ifdef __cplusplus

Hi all
This is my first post in this forum. If there is any mistake please forgive me.
I have some functions in C code to which variables are passed from C++ files OR some functions in C files are called from C++ file.
Will it be right if I enclosed definition of those functions in #ifdef __cplusplus ... #endif block in C file? Will those functions be called from C++ file ? OR I have to convert that C file to C++ file... Those functions are defined in so many C files, also there are some variables in C++ files which are used in C files...As the quantity of C files is large,it will be headache to convert those C files to C++ files...
What is the best way to achieve it?

Please give me suggestions.... Right now I am following the #ifdef __cplusplus way & it is getting compiled, But I am not sure whether it will run successfully...

If you've already got code, then don't touch it. This is why C++ gives you extern C -- surround the function prototype in an extern C block and the linker will know not to mangle the names.

OR you can just recompile all the code -- don't touch it or edit it in any way (unless you're using reserved words like "class" or something), just add it to your project.