Gentlemen, all what u say is somewhat clear.

But, can you explain:
1) (very interesting to me)
I've scanf(%s, somebuf); in my program, and how do I know, the size to allocate for incoming text?
In general, can I use scanf function and avoid SYGFAULT? If I can't - nor static, nor dynamic, what should I do to handle and allocate in memory incoming string with unknown size.
2) This code is sometime works:

char *string;
scanf("%s", string);

Smometimes works, sometimes SYGFAULTs, why?
I do not allocate any memory to it, how can it work?

Regards! =)

As far as I know, you can't use scanf with the %s escape on untrusted input; there is no way to keep it from overflowing. You can use something like %50s, which says that you want to get at most 50 characters. I think that is 50+1 including the \0, but I didn't verify.

If that code snippet works, it is by chance. string had some uninitialized value in it, and it happened to be a memory address which was writable by you. This means you scribbled on a random part of your program's memory, and it might crash later on. Alternatively, the pointer could point to somewhere non-writable, in which case you will get a seg fault on the scanf(). This is one of the beautiful parts of debugging unititialized pointers: They may work fine until you change a completely unrelated bit of code, and then the program can start crashing.

Thanks for a clear explanation! =)
I successfully try to use read function instead of scanf like this:

chars = read(0, string, MAX_STRING_SIZE);

string[chars-1] = '\000';

and now it's clear with scanf. %)

hey dudes, soz for opening a thread thats more than a year since it's last post.

I hope ppl are still active here.

i cant seem to be able to open a file.

the specific line that seems to enjoy trowing seg faults at me is bolded

FILE*myfile = (FILE*)malloc(sizeof(FILE)*3000);
if((myfile = fopen("getline.txt","tr"))==NULL)
{
printf("\nFile couldnt be opened\n");
}
else
{
printf("\nOpened file: Catalogue");
char temps[20];
fgets(temps,19,myfile);
printf(temps);
for(i=0;i<argv;i++)
{
printf("\nOpened file: Catalogue");
GetLineOI(&myfile);
fclose(myfile)
}
}

whats going on?

oh and incase your all wondering, i've been programming in C for about 2 hours a week for the last 6 weeks so im definantly a noob.

can anyone help or is my prgram doomed to failure?

me =

oh dear! what's this!

you don't allocate space for the file pointer.
the C library worries about the file operations.
you just declare a FILE pointer,

FILE * myfile;

oh and also i know the file getline.txt exsists cause i have checked.

it has one line of text in it and that is "This is a test"

thanx dude

I changed it but myfile still == NULL when opened.

i know i worry ppl sometimes but that what noobs are for

blimey

where do we start!
it's a bit of a mess, sorry!

"tr" ? what mode is this? "r+" i take it?

argv?? don't you mean argc? argc is the count of args.

why so small? give yourself some room man!


Look at man perror
which will print out the error message like "file not found" etc.

man thanx from the bottom of my heart, you really saved the day.

I changed the tr in fopen("getline.txt","tr") to t

and changed char temps[20]; to 100

your suggestion about the argv and c i dont get and when i changed it, the compiler spat the dummy.

I got tr from the lecture notes (opens a text file for reading).

argv i took straight from the note as well (im doing first year programing at UNI in Australia so dont complain )

for a code i wrote all by my self im pretty proud of it.

thanx again for the help.

no no.

should be mode "+r"

look at man page for fopen.

do you know what you are doing with argv and argc?

hehe nope wouldnt have a clue what argv and c are but i know that i just want to read from the file, not write to it too, thats a seperate part of the program

AAAARRRRRGGG!

im now starting to get really anoyed with these lectures

i have:

char temp[100];
do
{
temp = fgetc(*myfile);
printf(temp);
}
while(temp)!=NULL);

yet it still segments, the warning i get while compiling is:

incompatible types in assignment

can anyone help, i have searched both Yahoo, AJ and google and not found any help.

the lecture notes say that this should be right but it doesnt seem to work.

what exactly did you intend this to do?????

maybe this


that is a syntax error usage of the printf function.

what im trying to do is read in a few lines of text from a file and print them to the screen

99% fixed, now i just gotta stop the damned thing from printing out the last line, cant seem to get it to stop when it gets to EOF.

i might try some if statements in there

oh how i love java, much better than C