strcat causes bus error

[bubbles19518]

Hey,

I have this struct

struct node {
char *subExpressionT illNow; // the current subexpression
int isWord; /* To check if this is a valid word to be written into dict.txt,
0 is false, 1 is true*/
struct node *paths[26]; // A subexpression can be followed by any of the 26 characters
};

and this is the code thats giving me a bus error

head->paths[letter]->subExpressionT illNow = (char *)malloc(sizeof (head->subExpressionT illNow) + sizeof(char));
head->paths[letter]->subExpressionT illNow = strcat(head->subExpressionT illNow,&c);

Its a tree of binary letters, I load them in one character at a time. If the word is "STEVE" You create a node S which subExpressionTi llNow has value of "S". Then you create a node T which has a subexpressionti llnow of "ST".

Not working right, no clue whats wrong. Any help is greatly appreciated.

[donbock]

struct node {
char *subExpressionTillNow;
...
};

head->paths[letter]->subExpressionTillNow =
        (char *)malloc(sizeof(head->subExpressionTillNow) + sizeof(char));

sizeof(head->subExpressionT illNow) gives you the size of a char pointer. What you want is the length of the string being pointed at.

What should you do if head->subExpressionT illNow is NULL?
Make sure you include space for a string-terminating null character.

sizeof(char) is "1" by definition. You can choose to add the expression or the constant. It won't make any difference.

[Banfa]

head->paths[letter]->subExpressionTillNow = strcat(head->subExpressionTillNow,&c);

I am guessing that c is of type char in this statement. This will not work and is likely to produce undefined behaviour because a string is a NULL terminated string of characters. The size of a string with 1 character in it is 2. If you want to do this you need to create a string containing c to use in strcat not just take the address of c.

[bubbles19518]

You were right. c was type char. I attempted to create a string and still get a bus error. I also upped malloc to 2 instead of sizeof(char).

	char cc[2];
	cc[1] = '\0';
cc[0] = c;
							head->paths[letter] = (node *)malloc(sizeof(node));
							head->paths[letter]->subExpressionTillNow = (char *)malloc(sizeof(head->subExpressionTillNow) + 2);
							head->paths[letter]->subExpressionTillNow = strcat(head->subExpressionTillNow,cc);
							head->paths[letter]->isWord = 0;
							head = head->paths[letter];

[weaknessforcats]

It's been a while since I have coded C but I think for strcat you need to start out with a C string. Like, one of 0 characters:

char* str = malloc(sizeof(char));

Then intialize the string to a null string:

str[0] = '\0';

And then just use strcat:

strcat(str, "weaknessforcats");

You should need to do addtional malloc's.

However, for strcpy you need to allocate memory for the copy:

char* newstr = malloc((strlen(str) +1) * sizeof(char))
strcpy(newsrtr, str);

[bubbles19518]

Thanks a lot! That did the trick! I ended up just strcpy()ing it instead of strcat()ing.