Program crashing when a function is used many times

Question

I need to use the algorithm of linked list in my program. I will explain quickly what it need to do:

My program generate a string with maximum size 2.000. I need to create a linked list of elements of the following type:

typedef struct List * News;


 struct List { 
 char * Text; 
 News next;
} ;

Since the maximum size of the struct is 2.000, to put the information of one struct it my text field, I want to use the exact size of the struct. So, I made the following function to create and add an element on the top of my linked list:

void InsertLL (News p, char M[]){

 char * text = (char *)malloc(strlen(M) * sizeof(char));
 strcpy(text, M);
 News s,t;
 t = malloc(sizeof(struct List));
 t-> Text = text;
 s=p;
 p=t;
 t -> next = s;

 }

The program run in a infinite loop, and after a while running, it crashes. Without the function InsertLL, it runs well (for example, if I don't care for the size of my struct and put it directly on my element). On debug mode, it doesn't crash, so I think it is some kind of memory problem that I couldn't solve yet.

is there something I am doing wrong when I call malloc?

Thanks for your help!

`char * text = malloc(1+ strlen(M) );` – wildplasser Oct 12 '13 at 18:39 — wildplasser, Oct 12 '13 at 18:39

Vallabh Patade · Answer 1 · 2014-07-29T18:47:33.823

3

You are not allocating enough space for text. You should consider space of null character as well so allocate strlen(M)+1 bytes.

sizeof(char) is always one byte and you need not to typecast the malloc result as void * is automatically and safely promoted to any other pointer type.

Change the code to char * text = malloc(strlen(M)+1);

edited Jul 29 '14 at 18:47

answered Oct 12 '13 at 18:39

Vallabh Patade

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`sizeof(char)` is implicit to be one so it is redundant and no good can come by casting the return value of `malloc`. – digital_revenant Oct 12 '13 at 18:46

score 1 · Accepted Answer · edited May 23 '17 at 11:50

1

You are not allocating space for the null terminator. Pass strlen()+1 to malloc when allocating strings. Remember that strlen() returns the length of the string excluding the null terminating character.

Note that sizeof(char) is 1 by definition, and that you should not cast the return value of malloc. Your code should be

char * text = malloc(strlen(M) + 1);

edited May 23 '17 at 11:50

Community

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answered Oct 12 '13 at 18:39

David Heffernan

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Program crashing when a function is used many times

2 Answers2