realloc help

[dan.goodridge]

I have this error 'realloc' : cannot convert parameter 1 from 'stock' to 'void *' but i cant seem to find why ive read about realloc() but i know i need to use malloc() first or calloc() i just cant seem to get the jist of the idea thanks

					printf("Lists stock\n");{
		
	FILE *fp;			//file pointer
		fp=fopen("stock.txt","r");




		stock mylist[50];


	while(1) /* infinite loop */


	
	fp=fopen("stock.txt","r");


malloc( 1000 * sizeof( struct stock) == NULL );


  Nfields = fscanf(fp, "'%d %s %d\n", &mylist[i].product_id, &mylist[i].product_name, &mylist[i].stock_level); /* fscanf returns the number of fields it successfully read */


  if(Nfields != 3)  /* if we didn't read three fields, we're at the end of the data */


	  break;


   mylist = realloc(mylist[i], (i +1) * sizeof(struct stock)); /* or whatever you called the structure */ 


  if(!mylist)




mylist[i].product_id;
strcpy(mylist[i].product_name,pointer);
mylist[i].stock_level;
{
printf("Product Name:%s\n",mylist[i].product_name);


printf("Product_ID:%d\n ",mylist[i].product_id);
	
printf("Stock Level:%d\n\n",mylist[i].stock_level);  
}

[anduril462]

Your indentation is atrocious. If your code looks that crappy, it will be easy to make mistakes and hard to find or fix them. Read this: SourceForge.net: Indentation - cpwiki.

It's hard to give complete help when you omit relevant pieces of code like the definitions of stock and struct stock types.

I think you need to do some reading up on arrays and structs, and dynamic memory allocation. You don't actually need to use malloc/calloc first, the right call to realloc, or the right initialization of variables passed to realloc, will make it behave like malloc.

malloc( 1000 * sizeof( struct stock) == NULL );

That's broken in several ways. You don't set the value of malloc to anything, so you just allocate memory and throw it away, causing a memory leak. That == NULL does not belong in there. You should check the return value of malloc (or the pointer you assign it to) for NULL.

stock mylist[50];
...
mylist = realloc(mylist[i], (i +1) * sizeof(struct stock));

You can't assign a new chunk of memory to an array address. You probably want to make mylist a struct stock pointer, without the array bit*. Also, what is i here? It is potentially uninitialized, meaning you could realloc any number of bytes. Also, decide if it is mylist or mylist[i] you want to malloc/realloc memory into. They are not the same thing. As for your specific error message, "cannot convert parameter 1 from 'stock' to 'void *'", realloc takes a pointer to memory already allocated by malloc/calloc/realloc, or NULL (if NULL, it behaves just like malloc). But mylist[i] is a stock object, not​ a pointer to anything.

Also, you need to use a temporary value to store the result of realloc, and check it for NULL, before you assign it to your old pointer. Otherwise you run the risk of another memory leak.

* I can't tell, without the definition of stock and struct stock types, whether that is actually an array of pointers, though the error message you get suggests it's not. If it is, please change it. typedef'ing pointers is generally not a good idea.

[dan.goodridge]

is there an easier way to print out my entire text file?

[anduril462]

If you just want to print it, there is no need to read it into an array, whether statically or dynamically allocated. Just have a single struct, statically declared, read into that and print the data. Then your next iteration of the loop will read into the same struct, overwriting the old data, then you will print that out.

struct stock s
fp = fopen
while (fscanf(fp, "...", &s.product_name, ...) == 3)
    print stuff
fclose(fp)

[dan.goodridge]

then it just prints out loads of random numbers

case 3:
					printf("Lists stock\n");
{
		
	FILE *fp;			//file pointer
    fp=fopen("stock.txt","r");
	stock mylist[50];






while (fscanf(fp, "%s  %d  %d", &mylist[i].product_name,&mylist[i].product_id,&mylist[i].stock_level) == 10)
    	
			printf("Product Name:%s\n",mylist[i].product_name);


			printf("Product_ID:%d\n ",mylist[i].product_id);
	
			printf("Stock Level:%d\n\n",mylist[i].stock_level);  // start to process your data / extract strings here...
		
fclose(fp);


	


}
	break;

[anduril462]

How many things do you expect fscanf to read when you give it "%s %d %d"?

[Salem]

> while (fscanf(fp, "%s %d %d", &mylist[i].product_id,&mylist[i].product_name,&mylist[i].stock_level) == 10)
Where the ........ did you get 10 from?

You had 3 in your first post FFS.

[dan.goodridge]

ok edited it

case 3:
					printf("Lists stock\n");
{
		
	FILE *fp;			//file pointer
    fp=fopen("stock.txt","r");
	stock mylist[50];






while (fscanf(fp, "%s,%d,%d",&mylist[i].product_name,&mylist[i].product_id,&mylist[i].stock_level) == 3)
      
			printf("Product Name:%s\n",mylist[i].product_name);


			printf("Product_ID:%d\n ",mylist[i].product_id);


			printf("Stock Level:%d\n\n",mylist[i].stock_level);  // start to process your data / extract strings here...
	
			
		
fclose(fp);


	


}
	break;	


;

[anduril462]

This isn't Python, so merely indenting your printf statements wont make them all subordinate to the while loop. You need some curly brackets.

[dan.goodridge]

when i put in curly brackets it jumps the printf statement and goes straight to break.

[anduril462]

Post your new code.

[dan.goodridge]

heres the code

case 3:					printf("Lists stock\n");
{
		
	FILE *fp;			//file pointer
    fp=fopen("stock.txt","r");
	stock mylist[50];






while (fscanf(fp, "%s,%d,%d",&mylist[i].product_name,&mylist[i].product_id,&mylist[i].stock_level) == 3)
{
	
			printf("Product Name:%s\n",mylist[i].product_name); // print product name


			printf("Product_ID:%d\n ",mylist[i].product_id); //print product id


			printf("Stock Level:%d\n\n",mylist[i].stock_level);  // print stock level
	break;	
}
		
fclose(fp);

[anduril462]

Look at lines 23 and 24. What does the 'break' keyword do?

[dan.goodridge]

o i have the break in the wrong place it just jumps to case 4 with it being at that point

[dan.goodridge]

it was to print results then end program