Question

I have a character pointer that points the begining of a string and an index less than the length of the string. Now I want to create a pointer to point a substring of original string from the begining to the index or a substring with above constraints. Please help me to find a way to get it done. Here is a bit of the code:

char* ch="323+465";//this is the original string
int index=2;  //this is the index upto which I wish to create a substring, 
              // in java, it would have been ch.substring(0,3), if ch were a String

Thanks in advance.

Answer 1

Make a copy of a suitable number of characters:

char * substr = malloc(index + 2);
strncpy(substr, ch, index + 1);
substr[index + 1] = 0;

// ...

free(substr);

If you’re happy to mutilate the original string, just insert a null byte:

ch[index + 1] = 0;

The odd + 1 comes from the fact that your index seems to be inclusive, which is generally a bad idea.