Seg Fault in Knowledge Tree - c

Question

I am implementing a knowledge tree in c that can read from a file. I am getting a seg fault in my newStr function. I'm not able to test the rest of my code with this problem. I don't have much experience with c. Any help would be greatly appreciated.
my .c file
#include
#include
#include"animal.h"
#include
#include
/*returns a new node for the given value*/
struct Node * newNode (char *newValue)
{
struct Node * tree;
tree = (struct Node*)malloc(sizeof(struct Node));
tree -> value = newStr(newValue);
return tree;
}
/* returns a new string with value passed as an argument*/
char * newStr (char * charBuffer)
{
int i;
int length = strlen(charBuffer);
char newStr;
if(charBuffer[0] == 'A' || charBuffer[0] == 'Q'){
for(i=1; i<length; i++)
newStr += charBuffer[i];
}
return (newStr + "\0");
}
/*Read from a File and create a tree*/
struct Node * readATree(FILE * f)
{
char c;
char buffer[100];
struct Node * newTree;
c = fgetc(f);
if (c == 'A'){
fgets(buffer, 100, f);
newTree = newNode(buffer);
newTree -> left = NULL;
newTree -> right = NULL;
}
else{
fgets(buffer, 100, f);
newTree = newNode(newStr(buffer));
newTree->left = readATree(f);
newTree->right = (struct Node *) readAtree(f);
}
return newTree;
}
/*Write Tree to a File*/
void writeAFile(struct Node* tree, FILE * f)
{
char buffer[100];
strcpy(buffer, tree->value);
if(tree != 0){
if(tree->left == NULL && tree->right == NULL){
fputc((char)"A", f);
fputs(buffer,f);
} else{
fputc((char)"Q",f);
fputs(buffer,f);
writeAFile(tree->left, f);
writeAFile(tree->right,f);
}
}
}
/*The play should start from here*/
int main (){
struct Node* node;
struct Node* root;
char ans[100];
char q[100];
FILE * f;
f = fopen("animal.txt", "r+");
if(f != NULL)
readATree(f);
else{
node = newNode("Does it meow?");
node->right = NULL;
node->right->right=NULL;
node->left->left=NULL;
node->left=newNode("Cat");
root = node;
}
while(node->left != NULL && node->right != NULL){
printf(node->value);
scanf(ans);
if(ans[0] == (char)"Y" || ans[0] == (char)"y")
node = node->left;
else if(ans[0] == (char)"N" || ans[0] == (char)"n")
node = node->right;
else
printf("That is not a valid input.\n");
}
if(ans[0] == (char)"Y" || ans[0] == (char)"y")
printf("I win!");
else if(ans[0] == (char)"N" || ans[0] == (char)"n"){
printf("What is your animal");
scanf(ans);
printf("Please enter a yes or no question that is true about %s?\n", ans);
scanf(q);
node->right = newNode(q);
node->right->left = newNode(ans);
node->right->right = NULL;
}
writeAFile(root,f);
fclose(f);
return 0;
}
.h file
#include
struct Node {
char *value;
struct Node * left;
struct Node * right;
};
struct Node * newNode (char *newValue) ;
char * newStr (char * charBuffer);
struct Node * readATree(FILE * f);
void writeAFile(struct Node* tree, FILE * f);

Answer 1

There might be several more, but here's some points on what's wrong:
Your newStr function is just very,
very wrong. At a guess you'd want
something like:
char * newStr (char * charBuffer)
{
char *newStr;
if(charBuffer[0] == 'A' || charBuffer[0] == 'Q') {
newStr = strdup(&charBuffer[1]);
} else {
newStr = strdup("");
}
if(newStr == NULL) {
//handle error
}
return newStr;
}
You can't cast a string to a char
like you do here:
if(ans[0] == (char)"Y" || ans[0] == (char)"y")
Do instead(same for similar code
elsewhere too)
if(ans[0] =='Y' || ans[0] == 'y')
Same as above when you call putc,
don't do
fputc((char)"A", f);
Do
fputc('A', f);
scanf needs a format string, don't
do:
scanf(ans);
Do e.g. (or just use fgets again)
if(scanf("%99s",ans) != 1) {
//handle error
}

Answer 2

char * newStr (char * charBuffer)
{
int i;
int length = strlen(charBuffer);
char newStr;
if(charBuffer[0] == 'A' || charBuffer[0] == 'Q'){
for(i=1; i<length; i++)
newStr += charBuffer[i];
}
return (newStr + "\0");
}
Well, there's a few interesting things here... To get down to brass tacks, you're trying to copy the contents of a character pointer into another and this function isn't going to do that. All you're really doing is summing the value of each char in charBuffer into newStr because a char is really just an 8-bit integer and then you return that integer as a pointer through an implicit cast so it is now being treated as a memory address.
You should look to use strdup(), as has been noted, since this is exactly what the function is supposed to do. No need to reinvent the wheel. :)

Answer 3

"+" operator as string concatenation does not work in c.
If you actually want to copy the a string use strdup(). This function allocates memory and copies the string into it.
Don't forget to free the allocated memory when done using it.