somethingwrong with insert program

Hi all,
I wrote the following program to insert one string into another at a location specified by an integer n.
The program compiles without errors but does not produce the desired results, just outputs : hello, when I want it to output heltherelo
Please let me know waht I am doing wrong.
Thanks a lot.


#include<stdio.h>

void main(void)
{
void insertstring (char str1[], char str2[], int n);
char str1[] = {"hello"};
char str2[] = {"there"};
int n = 4;
int i;

insertstring("hello", "there", 3);
printf("%s\n", str1);
}

void insertstring (char str1[], char str2[], int n)
{
int i, j, x, len1;
char tmp[20];
len1 = strlen(str1);


/*copy str1 into tmp*/
for(i = n, x = 0; i <= len1; i++, x++)
tmp[x] = str1[i];

/*copy str2 into str1*/
for(j = 0; str2[j] != '\0'; j++)
str1[n + j] = str2[j];

str1[n + j + x] = '\0';
}

Try passing in the actual strings you created in your main function instead of explicitly writing them again...so change:

insertstring("hello", "there", 3);

to ..

insertstring( str1, str2, 3 );

Code:

---

printf("%s\n", str1);

---

will print hello unless you pass str1 as a parameter to "insertstring()".

Code:

---

insertstring(str1, "there", 3);

---

Moreover, str1 should be created with enough space to accomodate the new string.

Here's how it is done.

[CODE]
#include <stdio.h>
#include <string.h>

int main() {
void insertstring(char s1[], char str2[], int n);
char str1[20] = "hello", str2[] = "there";

insertstring( str1, str2, 3 );
printf("%s\n", str1);

return 0;
}

// not really clean code
void insertstring(char s1[], char s2[], int n) {
char tmp[20];

strncpy( tmp, s1, n );
tmp[n] = '\0';

strcat( tmp, s2 );
strcat( tmp, &s1[n] );

strcpy( s1, tmp );
}
[\CODE]

I would use pointers to strings and ++ the pointers. Without them it is longer but works.

Code:

---

//call it with these vars
char        *tmp=NULL;//pointer to a string so we always have the mem needed
char        str1[]="test me",str2[]="add";
int                n=2,len1,len2;

        len1 = strlen(str1);
        len2 = strlen(str2);
        tmp=(char*)malloc(len1+len2+1);//alloc some mem, add one for the '\0'
        if(tmp==NULL) return FALSE;//mem error

        if(insertstring (str1, str2, tmp, n))//if returns TRUE there is no error
        {
                free(tmp);
        }



int insertstring (char *str1, char *str2, char *total, int n)
{
        int        i, len1,len2;
        len1 = strlen(str1);
        len2 = strlen(str2);

        if(n>=len1) return FALSE;//not enough chars in the first string to add it there

        for(i = 0; i < (len1+len2); i++)
        {
                if(i<n) 
                        total[i] = str1[i]; //copy in string 1 up to the point we need to add
                else if( (i>=n) && (i<(n+len2)) )
                        total[i] = str2[i-n];  //copy in the second string starting at point n
                else
                        total[i] = str1[i-len2]; //add remainder of first string
        }
        total[len1+len2]='\0';//terminate
        return TRUE;//good
}

---

Thank you guys. I just have a quick question on the correction. why is it does not print the changed string if I pass it to it the way I did.
Thanks

For a simple reason that the contents of str1 are not stored where "hello" - insertstring("hello", "there", 3) is stored
and
the contents of str2 are not stored where "there" - insertstring("hello", "there", 3) is stored.

Code:

---

insertstring("hello", "there", 3);

---

When called, the two strings "hello" and "there" are stored randomly somewhere in memory, and it is this address that you are trying to manipulate while the actual strings you want to modify are stored in: &str1[0] and &str2[0]