Thread: Accessing next entry in a queue.

I just went over the instructions and found out that I was not expected to handle a situation in which the user enters more than 100 chars (i.e. "cleaning" those supplementary chars from the buffer), but I am expected to ascertain that the string which is moved to the struct does not exceed 100 chars. Does that mean that I should simply limit the string itself to [100], or does that also entail a slightly different format of scanf() (for instance, something like "%s100", if such syntax even exists; if not, a variation thereof then)? I'd appreciate some advice.

Would it serve me better in this case to use strncpy() and strncmp() (instead of strcmp() and strcpy()), in addition to scanf("%100s")? If so, what should I put as the third argument? Would it be 101 or strlen(str1)?

Instead of using scanf("%100s"), would it be safer then to read a char (perhaps via getch()) in a loop iterating to 100? Would that be a better way to approach this vis-a-vis the reuirement of assuring that the user did not enter more than one hundred chars?
For the sake of clarity, the requirement reads thus (verbatim):
"when reading a driver's name, you are asked to make sure the specific string will not exceed 100 chars. You are not expected to handle a case where the user entered more than 100 chars (for example, by cleaning the remaining chars from the buffer)".

If I'm understanding correctly, the requirements basically say "the string for the drivers name will be up to, but not exceeding, 100 chars". That means your string should be of size 101 (100 + 1 for the null terminator), but you don't need to worry about somebody typing 101 chars, so you don't really need length limits on your read functions, however they are a good idea anyway, and wont hurt in this case.

You should learn to look up and read the full documentation for the standard functions, it will answer many of the questions you have posted in this thread, including whether scanf would assure user didn't exceed 100 chars. Here's a link: scanf(3): input format conversion - Linux man page. Read the part about maximum field width. It should answer your question about the 100 in scanf("%100s"). Note, if you read about the %s modifier, you will notice it stops on white space. That means reading a name like "Jon Doe" will not work, it will only scan "Jon". Hence the recommendation of %100[^\n] by vart in post #62.

Your idea of a getch loop would work, but it is pointless, it would provide basically the same functionality as scanf("%100[^\n]"), but with more opportunities for bugs. It certainly wouldn't be any safer, possibly less so if you introduced a bug (e.g. potential buffer overflow).

Like that?:

Code:

	while (system->driversQueue){
		free(system->driversQueue);
		system->driversQueue = system->driversQueue->next;
	}
	while (system->ordersQueue){
		free(system->ordersQueue);
		system->ordersQueue = system->ordersQueue->next;
	}
	free(system);

I mean, would that be enough?

Well, I apologize for being impatient, but perhaps someone else would be willing to kindly answer whether the above code indeed frees the entirety of the struct as needed?

Originally Posted by peripatein

Like that?

You shouldn't use a pointer after freeing it. You'll need to use a temp pointer in your free loops to fix this.

My bad. I shall fix it and re-post shortly.

May you please confirm that this is what you meant I should do?:

Code:

void freeSystem(TaxiSystem* system){
	TaxiSystem *tmpdrv = system->driversQueue;
	TaxiSystem *tmpord = system->ordersQueue;
	while (tmpdrv){
		system->driversQueue = tmpdrv;
		tmpdrv = tmpdrv->next;
		free(system->driversQueue);
	}
	while (tmpord){
		system->ordersQueue = tmpord;
		tmpord = tmpord->next;
		free(system->ordersQueue);
	}
	free(system);
}