Segmentation Fault due to strcpy

[meepror]

Hi,
I bet you've all been asked this a million times but here goes! :)

I'm coding an English language dictionary which is stored in a tree by way of the following structure:

#define MAXWORDSIZE 100
 
typedef char word[MAXWORDSIZE];
typedef struct dictionary *dict;
 
 struct dictionary {
   dict left,right;
   word theword;
 } ;
 

Now comes the problem; I've written a function which adds a word into the appropriate null left/right leaf; which should work as intended apart from the following line which I singled out as causing a segmentation fault (using GDB & note that w is a char w[] argument of the function and that a dict d is also passed):

strcpy(d->theword, w);

I believe this is due to the fact that I've not allocated memory (using malloc) to the 'theword' element of 'd'.

I have attempted to do this using the following code on the line above the 'strcpy' line:

d->theword = (char *) malloc(sizeof(d->theword[MAXWORDSIZE]));

But I am getting these errors from that line:

error: incompatible types in assigment

By this you have all probably realised that I'm very new to C's menial ways but if anyone could give me a simple indication of how to fix this I'm sure I could go ahead and complete my program.

Thanks in advance,
P

[weaknessforcats]

You have typedef'd a char array of MAXWORDSIZE as word.

In C and C++, the name of an array is the address of element 0. That makes word the address of the MAXWORDSIZE array. You can't overstore that address with one form malloc since that would change the address of a lopcal variable.

As a sidelight, I would not use fixed arrays of MAXWORDSIZE because a word like FOX would occupy 100 bytes. Instead, I would make the struct member a char* and I would allocate using malloc the exact length of the word plus 1 for a null terminator and then do the strcpy.

[meepror]

Thank you for your response! I'm not at liberty to change the definition of the structure as it's defined in a header file that I don't have access to.

I have, however, taken into account what you said as regards the type mismatch and have come up with a statement that should be allocating correctly but still chokes up a Segmentation Fault upon running.

 
int len = strlen(d->theword)+1;
*d->theword = (char *) malloc(len); 
strcpy(d->theword, w);
 

I've still no idea what I could have done wrong; the only notion is perhaps that I'd want to assign the length of w to the malloc and not the length of the d->theword. But my take on this is that the length of d->theword should be defined as word is; a length of MAXWORDSIZE?

On a slightly lighter note; I miss Java!

[weaknessforcats]

have, however, taken into account what you said as regards the type mismatch and have come up with a statement that should be allocating correctly but still chokes up a Segmentation Fault upon running.


Code: ( text )
int len = strlen(d->theword)+1;
*d->theword = (char *) malloc(len);
strcpy(d->theword, w);


I've still no idea what I could have done wrong;

You didn't read my post accurately. I said to allocate the length plus 1 more byte for the null terminator.

d->theword = (char*) malloc(len + 1);
 

BTW, what's with the *d?? If d is a pointer to dictionary variable then you use d->theword. If d is a pointer to a dictionary and you use *d then you have a dictionary and have to switch to member-of syntax (*d).theword. The preferred syntax is d->thewword. It's wasier to read.

I am assuming at this point that you have the word declared as a char* and not as an array.