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

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);

    }
}