/* app_path
 *
 * get application path, it need argv[0], and store the result to path.
 *
 * */ 
char * app_path(char * path, const char * argv0)
{
    char buf[PATH_MAX];
    char * pos;
    if (argv0[0] == '/') {    // run with absolute path
        strcpy(buf, argv0);
    } else {    // run with relative path
        if(NULL == getcwd(buf, PATH_MAX)) {
            perror("getcwd error");
            return NULL;
        }
        strcat(buf, "/");
        strcat(buf, argv0);
    }
    if (NULL == realpath(buf, path)) {
        perror("realpath error");
        return NULL;
    }
    return path;
}