getOpsFromSelf() (Long Post)

[Mike Sanders]

Just thinking aloud... Imagining here allowing more advanced users of
my app to modify a string of digits residing at the end of my project's
binary/exe. When the app loads, it reads in those digits. So far (knock
on wood), I've not run up against a single case where the code below has
failed to work under multiple OSs. A method mostly for power user's.

The user simply opens the compiled project in their favorite hex editor
& modifies the pre-existing string, a pseudo bitmask of sorts. Certainly
the user could unwittingly add/remove bytes rather than only modifying the
bytes, still its a nifty idea. But practical? I'm not so sure on that point.

Any other gotchas of note?

int main(int argc, char *argv[]) {

#ifdef WIN
getOpsFromSelf(NULL);
#else
getOpsFromSelf(argv[0]);
#endif

// work

return 0;

}

void getOpsFromSelf(char *fname) {

#ifdef WIN
char path[MAX_PATH];
GetModuleFileName(NULL, path, MAX_PATH);
#else
char path[PATH_MAX];
char *tmp = getpath(fname);
strncpy(path, tmp, sizeof(path));
path[sizeof(path) - 1] = '\0';
free(tmp);
#endif

FILE *bin = fopen(path, "rb");
if (bin == NULL) return; // return if file cant be opened

fseek(bin, -3, SEEK_END); // jump 3 bytes before end of file
unsigned char bytes[3];
fread(bytes, 1, 3, bin);
fclose(bin);

// ensure last 3 bytes are digits, else return
for (int i = 0; i < 2; i++) if (!isdigit(bytes[i])) return;

// assign values from bytes
ops.x = (bytes[0] == '1' || bytes[0] == '2') ? bytes[0] - '0' : 1; // 1-2
ops.y = (bytes[1] == '1') ? bytes[1] - '0' : 0; // 0-1
ops.z = (bytes[2] == '1') ? bytes[2] - '0' : 0; // 0-1

}

#ifdef NIX

char *getpath(char *fname) {

const char *PATH_SEPARATOR = ":"; // unix-like
const char *DIR_SEPARATOR = "/"; // unix-like
const int MAX_SIZE = 1024;

struct stat buffer;

if (stat(fname, &buffer) == 0) {
char *result = strdup(fname);
if (!result) return NULL; // memory allocation error <--
return result;
}

char *path_env = getenv("PATH");
if (!path_env) return NULL;

char path_env_copy[MAX_SIZE];
strncpy(path_env_copy, path_env, sizeof(path_env_copy));
path_env_copy[sizeof(path_env_copy) - 1] = '\0';

char full_path[MAX_SIZE];
char *dir = strtok(path_env_copy, PATH_SEPARATOR);

while (dir) {
snprintf(full_path, sizeof(full_path), "%s%s%s", dir,
(dir[strlen(dir) - 1] == DIR_SEPARATOR[0] ? "" :
DIR_SEPARATOR), fname);
if (stat(full_path, &buffer) == 0) {
char *result = strdup(full_path);
if (!result) return NULL; // memory allocation error <--
return result;
}
dir = strtok(NULL, PATH_SEPARATOR);
}

return NULL;
}

#endif

--
:wq
Mike Sanders