Thread: String Concatenation Using Pointers No strcat()

Hi there,

I am having a bit of an issue when trying to concatenate strings using char * pointers.

Here is what I need:

I need to add a list of ID's to a string that is a SQL statement so that I can end up with:
SELECT DISTINCT Object_ID FROM Object_Interactions WHERE Object_ID IN ('UUID1', 'UUID2') ORDER BY Object_ID ASC;

Here is what I am doing:

Code:

struct object_type
{
    char	*id;		/* UUID = 32 chars length */
};

void strappnd(char *dest, char *src)
{
	/* appends one string to another */
	while (*src != '\0')
		*dest++ = *src++;

	*dest = '\0';
}

char *buffer = NULL;
char *sql = NULL;
int j = 0;
int buffer_size = 0;
int object_count = 0;		

object_count = 2;		/* this is actually a calculated value... */

/* I have used malloc() and then assigned a value to object_list[j]->id and that was OK */

buffer_size = 32 * object_count + strlen("''") * object_count + strlen(", ") * (object_count - 1) + 1;

buffer = (char *)malloc(buffer_size * sizeof(char));	/* I know about pointer casting issue and malloc without stdlib.h but there is too much code to be changed... */
strcpy(buffer, "");

for (j=0; j<object_count; j++)
{
	printf("buffer=%s\n", buffer);
	
	strcat(buffer, "'");	
	strappnd(buffer, object_list[j]->id);
	
	/* we must not end the sequence with a comma */
	if (j < object_count - 1)		
		strcat(buffer, "', '");
	else
		strcat(buffer, "'");
}
sql = (char *)malloc((100 + buffer_size + 1) * sizeof(char));
sprintf(sql, "SELECT DISTINCT Object_ID FROM Object_Interactions WHERE Object_ID IN (%s) ORDER BY Object_ID ASC;", buffer);
free(buffer);	

printf("sql=%s\n", sql);

Result:
sql = SELECT DISTINCT Object_ID FROM Object_Interactions WHERE Object_ID IN (UUID1') ORDER BY Object_ID ASC;

I have been trying and searching for a couple of days for all kinds of solutions but I can't seem to find anything and I can't make it work.
Basically the question is how to transform a const char * into a char *. Does simple casting work? Is it safe? What else can I do because
I keep hitting this wall, and I can't use the standard <string.h> functions because most of them expect a char const * as opposed to
char * in one of the arguments.

I have been looking on the Internet and forums, but for most cases strcat is being used and seems to be enough.
I found interesting variations of strcat, but they don't seem to work and I don't have any more time for this. After finding libAPR I even
thought of using it, but I only need one function from this library and plus the application must be portable on Linux, Mac, Windows...

Any help on how to do string concatenation with char * or how to convert const char * to char * would be greatly appreciated.

Other than that, C is just great.

Thanks in advance,
Ovidiu Anghelidi
[email protected]

>> Result:
>> UUID1'
Your code is showing the last "id" enumerated in the loop because "strappnd" is performing an "strcpy".

Why not use strcat()? Is "id" not a null-terminated C-string?

gg

http://www.tek-tips.com/viewthread.c...1433328&page=1