C / linked list / How can fix the segmentation fault? - c

Question

When I complie it, it has segmentation fault at
strcat(arr, cur->texts); which is in dumpTB function.
In main function, when the dumpTB function is called, it should print out like
hello\ngood bye\nworld\n same as what I have typed in newTB function..
Can anyone figure out what the problem is?
I have added the function called deleteTB(TB tb, int from, int to).
I'm not just asking like 'Can you do this for me?', i want to know and learn how to fix.
I tried from last night.. but still stuck..
Weirdly, I got a seg fault at the same line 'strcat(arr, cur->texts)'. I tried to modify different way and code differently.. but don't know.
Since my input is like, "hello\ngood bye\nworld\n"..
when the deleteTB(list , 0 , 1) is called like this, // (head node is 0)
printbuffer(list) should print like,
POS 0 : world
then, dumpTB(list) should print like,
world.
since i didn't know the rule in here, i have posted pretty much same thing last night which made people annoyed. Sorry for that. And i'm not just asking you guys to do it. I really want to learn.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "textbuffer.h"
#define MAX_TEXT 256
struct textbuffer {
char *texts;
int count;
TB next;
};
TB newTB (char text[]){
TB newText = malloc(sizeof(struct textbuffer));
char *cpy = (char *)malloc(MAX_TEXT * sizeof(char));
TB head = newText; // Store the first node to return
strcpy(cpy,text);
newText->count = 0;
newText->next = NULL;
int i = 0;
int j = 0;
while( cpy[i] != '\0') {
if( j == 0) {
head->texts = (char *)malloc(MAX_TEXT * sizeof(char));
}
if(cpy[i] == '\n') {
head->texts[j] = '\0';
newText->count++;
head->next = malloc(sizeof(struct textbuffer));
head = head->next;
j = 0;
i++;
} else {
head->texts[j++] = cpy[i++];
}
}
head->next = NULL;
return newText;
}
void releaseTB (TB tb) {
TB head = tb;
TB tmp;
while(head != NULL) {
tmp = head;
head = head->next;
free(tmp->texts);
free(tmp);
}
}
char *dumpTB (TB tb) {
if(tb == NULL) {
return NULL;
}
TB cur = tb;
char *arr = (char *)malloc(MAX_TEXT * sizeof(char));
while(cur != NULL) {
if(arr == NULL) {
strcpy(arr,"");
}
strcat(arr, cur->texts);
if(cur->next != NULL) {
strcat(arr, "\n");
}
cur = cur->next;
}
return (arr);
}
int linesTB(TB tb) {
return (tb->count);
}
void printBuffer(TB tb){
TB curr = tb;
int i=0;
while(curr->next != NULL){
printf("POS %d : %s\n", i++, curr->texts);
curr = curr->next;
}
}
void swapTB(TB tb, int pos1, int pos2) {
if((pos1 < 0) || (pos2 < 0) || (pos1 > linesTB(tb)-1) || (pos2 > linesTB(tb)-1)) {
printf("**GIVEN LINES ARE OUT OF RANGE**\n");
abort();
}
TB cur = tb;
TB head = tb;
int i = 0;
char *tmp = (char *)malloc(MAX_TEXT * sizeof(char));
tb->texts = cur->texts;
while( i < pos1) {
cur = cur->next;
i++;
}
strcpy(tmp, cur->texts);
cur->texts = NULL;
i=0;
while( i < pos2) {
head = head->next;
i++;
}
cur->texts = head->texts;
head->texts = tmp;
}
void deleteTB(TB tb, int from, int to) {
if((from < 0) || (to < 0) || (from > linesTB(tb)-1) || (to > linesTB(tb)-1)) {
printf("**GIVEN LINES ARE OUT OF RANGE**\n");
abort();
}
TB cur = tb;
int i = 0;
for(i = 0; i < from; i++) {
cur = cur->next;
}
while( i <= to ) {
cur->texts = '\0';
free(cur->texts);
//free(cur);
cur = cur->next;
i++;
}
}
int main(int argc, char * argv[]) {
TB list = NULL;
list = newTB("hello\ngood bye\nworld\n");
printf("**THERE ARE %d LINES IN TEXTBUFFER**\n", linesTB(list));
printBuffer(list);
printf("**Dumping test**\n");
printf("%s\n",dumpTB(list));
printf("**Swapping test**\n");
swapTB(list, 0, 1);
printBuffer(list);
printf("**Deleteing test**\n");
deleteTB(list, 1, 1);
printBuffer(list);
printf("%s\n",dumpTB(list));
releaseTB(list);
return 0;
}

Answer 1

you are using strcat function. and the first argument is arr which is not null terminated.
So use, below code before using strcat
arr[0]='\0';
Also, check for cur->next in the loop like this.
while(cur->next != NULL)
Also, your releaseTB will give you segfault for the above said reason.
change the loop condition to
while(head->next != NULL)
Edit
char *dumpTB (TB tb) {
if(tb == NULL) {
return NULL;
}
TB cur = tb;
char *arr = (char *)malloc(MAX_TEXT * sizeof(char)); //VS throws error if we wont cast
arr[0]='\0'; // Null Terminated
while(cur->next != NULL) { // changed to cur->next
if(arr == NULL) {
strcpy(arr,"");
}
strcat(arr, cur->texts);
if(cur->next != NULL) {
strcat(arr, "\n");
}
cur = cur->next;
}
return (arr);
}
void releaseTB (TB tb) {
TB head = tb;
TB tmp;
while(head->next != NULL) { // Changed to head->next
tmp = head;
head = head->next;
free(tmp->texts);
free(tmp);
}
}