Programming

How does the program know the full path of itself when the program is running in certain diretory? BTW, I have no "argv" information of main() functino.

(The program is written in C++ on linux platform)

The call to getcwd() returns the path to the current directory. argv[0] contains the invocation of the current program, and can be used to infer the directory of the path to itself -- but not necessarily. If the program was invoked without any directory information and is invoked along the PATH variable, you can grab the PATH variable from the environ (getenv("PATH")) and traverse each element looking for the program itself (basename of argv[0]).

There's a function called realpath() which canonicalizes the pathname you provide to its argument. However, it's recommended NOT to use this in general, because you have to allocate memory for the return argument, but there's no way of knowing how large that memory allocation should be. (But realistically you can get away with 1k).

Unfortunately, realpath doesn't do any of the "real work" for you. You still have to traverse PATH to find the program's home directory.