Very strange behavior possibly involving strtok

[rainey]

I've encountered a very strange issue that may or may not be caused by strtok.

Let me first just say that I can work around this by writing the program a different way, but at this point I'm just puzzled as to why this is going on.

int main()
{
	char* buffer[2] = {0, 0};
	long size50, size10;

	readFile("50000words.txt", buffer[0], size50);
	readFile("10000words.txt", buffer[1], size10);

	char **a;
	
        //entryList and lookupList contain pointers to locations in buffer[0]/[1] respectively.
        char *entryList[numEntries],
		*lookupList[numLookups];
	int entryVals[numEntries],
		lookupVals[numLookups];

	const char delim[] = ", \n\r";
	
	int i = 0;
	entryList[0] = strtok(buffer[0], delim);
	
	cout << entryList[0] << endl;	//Tetraheism
	
	while(entryList[i] != NULL && i < numEntries)
	{
		entryVals[i] = atoi(strtok(NULL, delim));
		entryList[++i] = strtok(NULL, delim);
	}
	
	cout << entryList[0] << endl;	//Tetraheism
	cout << entryList[1] << endl;	//Chrisoms
	
	
	lookupList[0] = strtok(buffer[1], delim);
	
	cout << entryList[0] << endl;	//Tetraheism
	cout << entryList[1] << endl;	//Chrisoms
	
	i = 0;
	while(lookupList[i] != NULL && i < numLookups)
	{
		lookupList[++i] = strtok(NULL, delim);
	}
	
	cout << entryList[0] << endl;	//chwartzlot  <---- WHAT? this string is towards the end of the buffer.
	cout << entryList[1] << endl;	//Chrisoms

So, I'm a bit puzzled as to exactly what could have happened here. Even more so because only pointed-to value of the first element of entryList has changed.

entryList[0] points to a location in buffer[0]. Casting entryList[0] to void* in the cout statement shows that the address pointed to changes. Can anyone explain why?

[tabstop]

You walk off the end of the lookupList array, by accessing lookupList[numLookups] which doesn't exist. (Since you're doing pre-increment, you get an off-by-one error even though the while loop "looks" right.)

[rainey]

Ah jeez, and here I was thinking it was some sort of ridiculous error caused by strtok.

I've spent too much time spent in the safety of Java. I guess I expected some sort of exception to be thrown by going out of bounds.

Thanks, fixed up the loops and it works fine now .