segmentation fault

[deepseawolf]

		
                if (search == 0)
		{
			non_linux = non_linux + 1; // just a counter
			printf("'%s' was not found in the linux or user dictionary\n", compare_word);
			printf("Do you want to add this word to your dictionary(1) yes, (0) no.\n");
			scanf("%d", &answer);
			
			if(answer == 1)
			{
				if(user_dictionary == NULL)
				{
					// prompt user one last time for the dictionary
					printf("File does not exist, one wil be created and appened the word");
					user_dictionary = fopen(dictionary_filename, "a+");	
					fprintf(user_dictionary, "%s ", compare_word); // HERE IS WHERE THE SEGFAULT IS
					fprintf(out, "%s%c ", compare_word, punct); // just some output
				}
				
				else
				{
					printf("File exists and will have the new word saved.\n");
					fprintf(user_dictionary, "%s ", compare_word);
					fprintf(out, "%s%c ", compare_word, punct);
				}
			}

so as i stated that is where it is, and i have no idea how to stop it? I need to open the user_dictionary append, read and write. and i need to write that word at the end of the file. but i always get a segfault. I commented it out and it worked fine, but i need to be able to write that word in there in order for it to stop asking the user if he wants to add it in.

[MK27]

Did you check to make sure the fopen() happens?

#include <errno.h>
#include <string.h>

if (!(user_dictionary = fopen(dictionary_filename, "a+"))) 
        perror("fopen fail:");

[quzah]

You never check to see if the file opens successfully. If you aren't closing it after using it elsewhere, your open will fail here.


Quzah.

[deepseawolf]

I used to, but i got tired of asking the user haha, so by this point i just open it with "a+" which should append to read and write and it will create its own file right?

[CommonTater]

How is user_dictionary defined?
How is dictionary_filename defined?
How is compare_word defined?

You are not checking the return value of fopen() so you don't actually know if the file is open or not.

[deepseawolf]

but when i ran it through gdb it says the fprintf is the one seg faulting and when i comment it out it will still run, so it couldnt be the fopen?

compare_word is a array of characters from another inputted file. user_dictionary is a file pointer to the file i am trying to append, and dictionary_filename is a file pointer to a linux dictionary i have

[CommonTater]

I used to, but i got tired of asking the user haha, so by this point i just open it with "a+" which should append to read and write and it will create its own file right?

The point is not to ask the user anything the point is to check the return value of the function call in user_dictionary to know if the file open activity succeeded or not.

FILE *user_dictionary;

user_dictionary = fopen("filename","a");
if (! user_dictionary)
  { puts ("Holy crap the file didn't open");
     exit (1); }

[quzah]

but when i ran it through gdb it says the fprintf is the one seg faulting and when i comment it out it will still run, so it couldnt be the fopen

No. If it fails to open, you are trying to write to an invalid file descriptor, so it's unsurprising that it crashes.

Quzah.

[deepseawolf]

					if (user_dictionary == NULL)
					{
					printf("test if it opened.\n");
					}

ya i just add that after my "user_dictionary = fopen(dictionary_filename, "a+");"
if its openning, why isnt my "fprintf(user_dictionary, "%s ", compare_word);" working?

[MK27]

but when i ran it through gdb it says the fprintf is the one seg faulting and when i comment it out it will still run, so it couldnt be the fopen?

Yes, probably because you are trying to print to a NULL handle because fopen() failed.

If you comment it out it will still work because (at least in your snippet), that file pointer is not used anywhere else.

You have to check and see if the file is open or not. If not, that is the the problem, mystery solved.

[deepseawolf]

oh crap... nvm if its NULL that means it didnt open, CRAP, whats wrong with my coding then if it isnt opening?

if they answer one. it the prompts them to input a file name.

user_dictionary = fopen(dictionary_filename, "a+");

if that code isnt openening the file then what else can i do?

and boom goes the dynamite, so i forgot to ask for the file name again, thank you every one for beating it out of me. Last day antics .

[MK27]

					if (user_dictionary == NULL)
					{
					printf("test if it opened.\n");
					}

Quite possibly this never prints because stdout has not been flushed when the seg fault happens. Ie, user_dictionary is NULL, and the message is in the stdout buffer when the crash happens (so does not get sent to the console). Always print to stderr (which is unbuffered) for debugging:

fprintf(stderr,"test if it opened.\n");

And try that way. If it still seems the file has opened properly, check the value of compare_word in gdb after the fault:

gdb> print compare_word

Could be that is going out of bounds.

[quzah]

You should only open it once. Never again. Either that, or in the same scope you open it, after you are done writing/reading, then close it, so you can open it again.

Simple C rules: If you open it, close it when you are done. If you allocate it, free it when you are done.


Quzah.

[deepseawolf]

gotcha, thank you every one

[CommonTater]

oh crap... nvm if its NULL that means it didnt open, CRAP, whats wrong with my coding then if it isnt opening?

if they answer one. it the prompts them to input a file name.

user_dictionary = fopen(dictionary_filename, "a+");

if that code isnt openening the file then what else can i do?

and boom goes the dynamite, so i forgot to ask for the file name again, thank you every one for beating it out of me. Last day antics .

Now... one more thing... if dictionary_filename is null (i.e. if your user presses enter without inputting anything) your fopen is going to fail... so you need to check the filename input by the user...

Error checking (within reason) is your friend....

And to expand on Quzah's rules... NEVER keep a file open or hang on to memory any longer than you have to.