Thread: strtok(), strdup() error

I don't really know how to even begin solving this problem. Basically, I have a structure:

Code:

struct Items{
char*desc;
char*name;
char*behave;
struct Areas*loc;
struct Items*next;
struct Items*prev;
USE_FUNCTION use;
};

I want to fill out the fields of the structure...

Code:

fgets (input, 255, file); if ((p = strchr(input, '\n')) != NULL) *p = '\0';
			new=createitem("NULL", "NULL", currentarea);
			name=strtok(input,","); 
			desc=strtok(NULL, ",");
			behavior=strtok(NULL, ","); 
			new->name=strdup(name); 
			new->desc=strdup(desc); 
			new->behave=strdup(behavior); 
			new->loc=&a[currentarea]; printf("%s", new->name);
			new->prev=NULL; new->next=NULL; printf("%s", new->name);

The problem here is that when I assigned new->prev and new->next to NULL, the value of new->name changes! Apparently it is resetting the value to NULL. I'm not sure why at all, but it is causing segmentation faults.

I changed the code slightly:

Code:

new->loc=&a[currentarea]; printf("%s", new->name);
			new->prev=NULL; printf("%s", new->name);
			new->next=NULL; printf("%s", new->name);

If the name is "paperweight", then it will print "paperweightpape" rather than the expected "paperweightpaperweightpaperweight"

This is the createitem() function:

Code:

Items*createitem(char*name, char*desc, int currentarea){

Items*new=(Items*)malloc(sizeof(Items*));
new->next=NULL;
new->prev=NULL;
new->behave=NULL;
new->desc=NULL;
printf("\nCreated: %p", new);
return(new);

}

There are more problems than you appear to realize...

First... if you are using fgets to load a line from the file, the companion function would be sscanf() to burst out your data. strtok() is destructive.

Second rather than using strdup() you should create actual char array[] space in your struct...

Code:

struct Items{
char desc[64];
char name[32];
char behave[16];
struct Areas*loc;
struct Items*next;
struct Items*prev;
USE_FUNCTION use;
};

Then you can use sscanf() to load the struct directly...

Code:

fgets(input, 255, file)
sscanf(%s,%s,%s", items.desc, items.name, items.behave)

Believe me, it's going to work a lot better than what you have.

Originally Posted by Adam Rinkleff

I might have just fixed it by changing this line: [Items*new=(Items*)malloc(sizeof(Items*));} to

Code:

Items*new=(Items*)malloc(sizeof(Items));

Could someone explain how exactly my code is affected by setting the malloc size to the size of a pointer. Obviously its the incorrect size, I just wonder what is happening.

So if you allocate four bytes for an object, and then try to write 437 bytes to that object, where are the other 433 bytes going to go? (Hint: on top of other things, is where.)