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]

It should be fine to pass ANY string INTO a const char * - it's only if you try to convert a const char * into a char * that you would be in trouble.

E.g.

Code:

---

int strlen(const char *s)
{
 ...
}

int main()
{
  char s[10] = "A string";

  s[2] = ' ';
  s[3] = 't';
  s[4] = 'h';

  printf("%s is %d long\n", s, strlen(s));
  return 0;
}

---

This should compile and work fine.

So I don't understand what the problem with const is in this case?

--
Mats

>> 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

Quote:

---

Originally Posted by Codeplug

>> 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

---

If it wasn't, then it also wouldn't work for the current code, which detects end by comparing to zero.

--
Mats

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