Thread: Segmentation faults out the ****

im really sorry that you had to type all that cause i understood everything upto

/* sizeof(temp) will typically be 4 on 32 bit systems. You probably want a value of about 19 */

and then you lost me.

what does "4 on 32 bit system" mean?

i mostly understand:

/* undefined behaviour. The buffer pointed at by loadedfile is not initialised */

do you mean that i have to say something like:

loadedfile = "a" or something?

if so can i initialise it to NULL?

Originally Posted by bithub

First of all, you're not allocating 599 slots. You're allocating 600 * sizeof(char*) slots which probably ends up being 600 * 4 = 2400 depending on your machine.

Second of all, how do you know the memory you've allocated is enough? You never check the file size beforehand, or keep track of how many bytes you are copying in to the loadedfile buffer.

Here is a better version of your function

Code:

void ReadCatalogue(FILE *myfile)
{
	char		*loadedfile;
	char		temp[512];
	int		buffersize = 600;
	int		bytescopied = 1; // start at 1 to account for null term

	loadedfile = malloc(buffersize);
	loadedfile[0] = '\0';  // so strcat() doesn't tank the first through the loop

	while(fgets(temp,sizeof(temp),myfile))
	{
		bytescopied += strlen(temp);
		if(bytescopied > buffersize)
			break; // break from while loop if buffer isnt big enough to copy everything
		strcat(loadedfile,temp);
	}
	printf(loadedfile);
}

i probably should have mentioned this earlier but two of the restraints i have are,
1. Only runtime memory is to be used.
an
2. You have to know what your doing.

im pretty sure the tutors would pick up on that code in no-time. sorry, normally i would use it and have you money in the mail, but i'd get more marks with what i have than if i dont know what the code does.

Well I'd rather have you understand it anyways. I didn't realize this was homework.

Basically, in your code you can stop the strcat() call from crashing your program by adding the following code after your malloc() statements:

Code:

loadfile[0] = 0;

strcat() appends a string onto another string. In order to make loadfile an empty string, you just need to make the first character a null terminator.

hey, quzah and bithub, ever consider tutoring first year uni students?

i tells ya, you'ed be great at it.

hehe, you guys must be really getting tired of my noobishness.

Code:

char *Catalogue = malloc(sizeof(*Catalogue)*10);
Catalogue = "a";
printf("What file would you like to load? ");
scanf("%9s",Catalogue);
ReadCatalogue(myfile);

segments here

if i try catalogue[0] = "a"; like was suggested earlier, then i get this warning

Code:

warning: assignment makes integer from pointer without a cast

this is really starting to ........ me off too, so im sorry for all those that read my code and start rocking in your chairs because of how bad it looks, but i dont do it on purpose.

i also get the same problem here:

thats fixed the warning, does anyone have any idea how to fix the porblem with the segmenting?

if i try the '&' thing infront of Catalogue in the fopen statement i get

Code:

warning: passing arg 1 of `fopen' from incompatible pointer type

and im really hesitant to fiddle with the code any more than i have to cause just my luck, it'll fall apat in my hands

i know you guys arent getting payed to do this, but if your here and are able to help, why not spread a little cheer by helping some-one in a real jam? pretty please with a cherry on top?

never mind, thanx guys i fixed it, but only with your expert help.

hey, just me again:

new segfault and this one aint my fault

Code:

char *temp = malloc(sizeof(*temp)*10);
temp[0]='a';
scanf("%9s",temp);

thats it, it segfaults at scanf and i dont know why.