Question 13.3

comp.lang.c FAQ list · Question 13.3

Q: Does C have anything like the ``substr'' (extract substring) routine present in other languages?

---

A: Not as such. (One reason it doesn't is that, as mentioned in question 7.2 and section 8, C has no managed string type.)
To extract a substring of length LEN starting at index POS in a source string, use something like

char dest[LEN+1];
 strncpy(dest, &source[POS], LEN);
 dest[LEN] = '\0'; /* ensure \0 termination */

or, using the trick from question 13.2,

char dest[LEN+1] = "";
 strncat(dest, &source[POS], LEN);

or, making use of pointer instead of array notation,

strncat(dest, source + POS, LEN);

(The expression source + POS is, by definition, identical to &source[POS] --see also section 6.)