CODEWITHSUNDEEP
c
dhimanta
dhimanta

Reputation: 219

Value Not printed right for second element of array

int main()
{
    char *a1[10] = {"123","121"};
    int i =0;
    char *a=NULL;
    for(i=0;i<2;i++)
    {
        a=strcat(a1[i],"0000");
        printf("values %s",a);

    }
}

Output of this code comes out to be this $ ./a.exe values 1230000 values 0000000

but it should be $ ./a.exe values 1230000 values 1210000

Please tell me where i am wrong

Upvotes: 2

Views: 99

Answers (2)

David Ranieri
David Ranieri

Reputation: 41036

You want an array of array of char, but char *a1[10] is an array of pointers to char (tipically placed in read-only segments / string literals), trying to modify a string literal usually leads to a segmentation fault.

Change

char *a1[10] = {"123","121"};    /* Array of string literals (read only) */

to

char a1[][10] = {"123","121"};  /* Array of array of char (read - write) */

Upvotes: 6

Serge Ballesta
Serge Ballesta

Reputation: 149085

The problem is not really the modification of string litterals. But the line 

char *a1[10];

affects an array of 10 char * and not a pointer to an array of char[10] what I suppose OP was expecting (as noted in Jdamian comments).

To create an array of char[10], you must write :

char a1[][10] = {"123","121"};

That way, you create an array of 2 char[10] initialized respectively to "123" (in fact, { '1', '2, '3, '\0', '\0', '\0', '\0', '\0', '\0', '\0'} as it is really a char[10]) and "121";

That way you can safely strcat "0000" to a1[i] because 3 (initial length) + 4 (added length) + 1 (terminating null) gives 8 <= 10.

But the really safe way would be :

a=strncat(a1[i],"0000", sizeof(a1[0]) - strlen(a1[i]) - 1);

Upvotes: 3

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