Thread: Warnings from String manipulation functions.

I'm using various standard string.h functions in a program that I am writing although I am obviously using them incorrectly. Although the program seems to work with these compiler errors (so far) I know that they indicate something is wrong and that the results expected to be returned may be undefined in some cases. I will try to show the appropriate lines of code in here so that you can see. The code as a whole is fairly long, so I will spare you all and just post little bits.

Code:

/* these are globals at the moment */
struct product
{
	float price;
	char *descript[80];
	int quantity;
	char *sku[5];
}
items[MAX_ITEMS];

*/ snip /*

/* here I simply try to compare the contents of a char string
 and a string literal? I store the result in the int j so that I can test the results
 of the compare /*

int j; 
j = strcmp(items[num_lines].sku, "q");

/* same type of deal here except with a strcopy. I am trying to copy the contents of 
the string desc, into the descript string (part of the product structure */

char desc[100];
strcpy (items[num_lines].descript, desc);

/* one final example. I open a file and try to  write the contents of the product structure 
to it, one attribute per line. Below I attempt 
to write a char string to the file. */

FILE *fp;
fputs(items[counter].sku, fp);

The warnings I get are like this... I'll post the three separate warnings that I get from the lines above. I get many more similar warnings than the ones above, but I think that if I can get some guidance on these, then I should be able to figure the rest out for myself.

Code:

register3.c: In function `main':
register3.c:82: warning: passing arg 1 of `strcmp' from incompatible pointer type
register3.c: In function `display_item':
register3.c:225: warning: passing arg 1 of `strcpy' from incompatible pointer type
register3.c:308: warning: passing arg 1 of `fputs' from incompatible pointer type

Thanks guys, I apologize if this crap is difficult to read. If more info is required, I will happily provide.

Cheers
Arker.

>j = strcmp(items[num_lines].sku, "q");
strcmp() takes the first argument as a pointer to a string and not a pointer to pointer to string, which is in your case. So, your code should look something like:

Code:

j = strcmp(items[num_lines].sku[0], "q");

But don't forget to allocate memory to each of the items[num_lines].sku[x]!

>fputs(items[counter].sku, fp);
Same applies here.

>the memory is allocated then?
No. Look closely what you have declared: char *sku[5];
The statement only impleis, you have declared 5 pointers, pointing somewhere in memory (probably some other program's address space, that's why you get the 'segfault' when you try to manipulate this!). Now, it's your duty to make these pointers point somewhere in YOUR program space, where you have allocated memory. That's where malloc() can help you. You can do:

Code:

sku[0] = malloc(100);
sku[1] = malloc(100);
sku[2] = malloc(100);
sku[3] = malloc(100);
sku[4] = malloc(100);

Where, 100 bytes are allocated for each of the pointers.

If you are not very clear with this, you can go by the simpler method as suggested by Hammer:

Code:

char sku[5][20];