lijewski@theory.tn.cornell.edu (Mike Lijewski) (10/30/90)
My understanding is that strings are no longer writable. That is to say,
the assignment to s[5] in the below program shouldn't be allowed.
main() { char *s = "testing"; s[5] = 'z'; }
Is a conforming implementation required to issue a warning, an error, or
what?
--
Mike Lijewski (H)607/272-0238 (W)607/254-8686
Cornell National Supercomputer Facility
ARPA: lijewski@theory.tn.cornell.edu BITNET: mjlx@cornellf.bitnet
SMAIL: 25 Renwick Heights Road, Ithaca, NY 14850gwyn@smoke.brl.mil (Doug Gwyn) (10/30/90)
In article <1990Oct29.174410.28498@batcomputer.tn.cornell.edu> lijewski@theory.tn.cornell.edu (Mike Lijewski) writes: >My understanding is that strings are no longer writable. They never have been guaranteed to be writable. >Is a conforming implementation required to issue a warning, an error, or >what? The standard says, "If the program attempts to modify a string literal of either form, the behavior is undefined." A diagnostic message is not required; in fact, some implementations may support this operation as a conforming extension.
bhoughto@cmdnfs.intel.com (Blair P. Houghton) (10/30/90)
In article <1990Oct29.174410.28498@batcomputer.tn.cornell.edu> lijewski@theory.tn.cornell.edu (Mike Lijewski) writes: > >My understanding is that strings are no longer writable. That is to say, >the assignment to s[5] in the below program shouldn't be allowed. > >main() { char *s = "testing"; s[5] = 'z'; } Correct. However, if you had done main() { char s[] = "testing"; s[5] = 'z'; } s would itself be an array and be writable; it is considered identical to having done main() { char s[] = {'t','e','s','t','i','n','g','\0'}; s[5] = 'z'; } (cf. ANSI X3.159-1989, sec. 3.5.7, p. 75, ll. 24-30) >Is a conforming implementation required to issue a warning, an error, or >what? "...the declaration char *p = "abc"; defines p with type `pointer to char' that is initialized to point to an object with type `array of char' with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to modify the contents of the array, the behavior is undefined." (ibid., ll. 30-34) Therefore, it's entirely up to your implementor. --Blair "Harder to find than to understand..."