help, please

**yafit** · 08-30-2010

Hi,

l'm getting an error when running the code below.
the error seem to be in the Bold line ("while..").

Code:

userIPF = (char *)malloc(NAME_MAX_LENGTH * sizeof(char));
    if (userIPF == NULL)
    {
        fprintf(stderr, "Error: Memory allocation error\n");
        if (crypt_func != NULL)
            free(crypt_func);
        if (crypt_func_str != NULL)
            free(crypt_func_str);
        fclose(ipf);
            return -1;
    }
 
    passwordIPF = (char *)malloc(PASSWORD_MAX_LENGTH * sizeof(char));
    if (passwordIPF == NULL)
    {
        fprintf(stderr, "Error: Memory allocation error\n");
        if (crypt_func != NULL)
            free(crypt_func);
        if (crypt_func_str != NULL)
            free(crypt_func_str);
        if (userIPF != NULL)
            free(userIPF);
        fclose(ipf);
            return -1;
    }

while (fscanf(ipf,"%s\t%s", userIPF, passwordIPF) == 2)
            {               
 
                        if ((strcmp(userIPF,user)==0) && (strcmp(passwordIPF, crypt_func_str)==0))
                {
                    found = 1;
                    break;
                }
                   
                if (userIPF != NULL)
                    free(userIPF);
                if (passwordIPF != NULL)
                    free(passwordIPF);

                userIPF = (char *)malloc(NAME_MAX_LENGTH * sizeof(char));
                if (userIPF == NULL)
                {
                    fprintf(stderr, "Error: Memory allocation error\n");
                    if (crypt_func != NULL)
                        free(crypt_func);
                    if (crypt_func_str != NULL)
                        free(crypt_func_str);
                    fclose(ipf);
                        return -1;
                }
                passwordIPF = (char *)malloc(PASSWORD_MAX_LENGTH * sizeof(char));
                if (passwordIPF == NULL)
                {
                    fprintf(stderr, "Error: Memory allocation error\n");
                    if (crypt_func != NULL)
                        free(crypt_func);
                    if (crypt_func_str != NULL)
                        free(crypt_func_str);
                    if (userIPF != NULL)
                        free(userIPF);
                    fclose(ipf);
                        return -1;
                }
 
            }

this is what Valgrind is giving me:

Code:

==28689== Invalid write of size 1
==28689==    at 0x510831F: _IO_vfscanf (in /lib/libc-2.9.so)
==28689==    by 0x51163E7: fscanf (in /lib/libc-2.9.so)
==28689==    by 0x40110B: main (authenticate.c:117)
==28689==  Address 0x5423464 is 0 bytes after a block of size 20 alloc'd
==28689==    at 0x4C278AE: malloc (vg_replace_malloc.c:207)
==28689==    by 0x400DCA: main (authenticate.c:81)
==28689==
==28689== Invalid write of size 1
==28689==    at 0x510BB91: _IO_vfscanf (in /lib/libc-2.9.so)
==28689==    by 0x51163E7: fscanf (in /lib/libc-2.9.so)
==28689==    by 0x40110B: main (authenticate.c:117)
==28689==  Address 0x5423470 is 12 bytes after a block of size 20 alloc'd
==28689==    at 0x4C278AE: malloc (vg_replace_malloc.c:207)
==28689==    by 0x400DCA: main (authenticate.c:81)
==28689==
==28689== Invalid read of size 1
==28689==    at 0x4C2832A: strcmp (mc_replace_strmem.c:337)
==28689==    by 0x400F98: main (authenticate.c:120)
==28689==  Address 0x5423464 is 0 bytes after a block of size 20 alloc'd
==28689==    at 0x4C278AE: malloc (vg_replace_malloc.c:207)
==28689==    by 0x400DCA: main (authenticate.c:81)

i don't understand why there's an error. Can someone please help me?

thank you.
(and sorry for my english)

**Adak** · 08-30-2010

You included stdlib.h, right?

I'd love to see you kick out fscanf(), and use the more robust fgets(buffer, sizeof(buffer), filePointerName);

Code:

while((fgets(buffer, sizeof(buffer), filePointer)) != NULL) {

}

I really like it, and I can't post about fscanf() much, since this is a family oriented forum.

**yafit** · 08-30-2010

Yes

**Bayint Naung** · 08-30-2010

Wonder why you can't just do this?

Code:

while (fscanf(ipf,"%s\t%s", userIPF, passwordIPF) == 2)
            {               
                 if ((strcmp(userIPF,user)==0) && (strcmp(passwordIPF, crypt_func_str)==0))
                {
                    found = 1;
                    break;
                }
            }

**yafit** · 08-30-2010

Because it doesnt work. We get the same error

**Bayint Naung** · 08-30-2010

Maybe your input overflow userIPF, passwordIPF...
And your file ipf is it opened successfully? Did you check that?
If your input are NAME_MAX_LENGTH long, you need to allocate +1 for null character which fscanf() will append.

**Adak** · 08-30-2010

And yet ANOTHER great reason to like fgets()!! < oh yeah! >

**yafit** · 08-30-2010

in our file, the strings are separated by "tab".
we tried to use fgets, but it doesn't work (we allocated enough memory to get it):

Code:

buff = (char *)malloc((sizeof(func)+NAME_MAX_LENGTH) * sizeof(char));

	if (buff == NULL)

	{

		fprintf(stderr, "Error: Memory allocation error\n");

		if (crypt_func != NULL)

			free(crypt_func);

		if (crypt_func_str != NULL)

			free(crypt_func_str);

		fclose(ipf);

        	return -1;

	}
while (fgets(buff, sizeof(buff), ipf) !=NULL){...}

**yafit** · 08-30-2010

our ipf opened successfully and we allocated enough memory

**Bayint Naung** · 08-30-2010

Provided that you've allocated enough memory, the only possible cause is because of your file pointer ipf.
Btw,

if ((strcmp(userIPF,user)==0) && (strcmp(passwordIPF, crypt_func_str)==0))

Where is user and crypt_func_str defined?

**yafit** · 08-30-2010

Thanks!!! it's working!!!

**Bayint Naung** · 08-30-2010

So What's the problem???

**yafit** · 08-30-2010

we changed it to fgets and made mistake in sizeof(buff)

**hk_mp5kpdw** · 08-30-2010

Code:

userIPF = (char *)malloc(NAME_MAX_LENGTH * sizeof(char));
...
passwordIPF = (char *)malloc(PASSWORD_MAX_LENGTH * sizeof(char));
...
userIPF = (char *)malloc(NAME_MAX_LENGTH * sizeof(char));
...
passwordIPF = (char *)malloc(PASSWORD_MAX_LENGTH * sizeof(char));

You should not cast the return value of malloc in C. Also, sizeof(char) is guaranteed to be 1 and so can be eliminated from the malloc call. The following should be sufficient:

Code:

userIPF = malloc(NAME_MAX_LENGTH);
...
passwordIPF = malloc(PASSWORD_MAX_LENGTH);
...
userIPF = malloc(NAME_MAX_LENGTH);
...
passwordIPF = malloc(PASSWORD_MAX_LENGTH);

**Salem** · 08-30-2010

Code:

        if (crypt_func != NULL)
            free(crypt_func);

Just do

Code:

            free(crypt_func);

free will accept a NULL pointer, and do nothing.
Besides, if crypt_func could be NULL, then you're in trouble when it comes to the strcmp calls later on.

Is there a reason why you don't do

Code:

char userIPF[NAME_MAX_LENGTH];

For you average length of name, on your average machine, this would significantly simplify the code.

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