1. string literal definition in c language 1> "hello world" // ok 2> L"hello world" // ok (wide character for representing chinese, japanese) 3> "i " "love " "you" // ok, apply string concetation 4> "i " "love " "you" // ok, apply string concetation 5> "" // ok, empty string 6> "hello world" // error 7> "hello / tworld" // error of c definition, but compile succeessfully in lcc & gcc [1]
2. call relationship
expression // expr.c, see primary(void)
|---> STRING_LITERAL_DFA // gettok()
|---> scanner // scon()
|---> get escape sequence // backslash()
|---> copy string literal into buffer // cput(), or wcput()
|---> storage buffer for string literal // char cbuf[BUFSIZE+1], or wchar wcbuf[BUFSIZE+1]
3. comment on source code
// comments on scanner of string literal, in lex.c
813 static void *scon(int q, void *put(int c, void *cl), void *cl) { 814 int n = 0, nbad = 0; // n counts how many characters in string literal 815 // q is the enclosing character, for example '/"'(double quotes) 816 do { 817 cp++; 818 while (*cp != q) { 819 int c; 820 if (map[*cp]&NEWLINE) { 821 if (cp < limit) // like 6> invalid occurence of literal string definition, goto error 822 break; 823 cp++; 824 nextline(); 825 if (cp == limit) // reach EOF, but without matching the enclosing character, goto error 826 break; 827 continue; 828 } 829 c = *cp++; 830 if (c == '//') { 831 if (map[*cp]&NEWLINE) { 832 if (cp < limit) // like 7> invalide occurence of literal string definition, goto error 833 break; 834 cp++; 835 nextline(); 836 } 837 if (limit - cp < MAXTOKEN) 838 fillbuf(); 839 c = backslash(q); // deal with escape sequence 840 } else if (c < 0 || c > 255 || map[c] == 0) // ? not sure of the use 841 nbad++; 842 if (n++ < BUFSIZE) 843 cl = put(c, cl); // stores string literals in cbuf[BUFSIZE+1] or wcbuf[BUFSIZE+1] 844 } 845 if (*cp == q) 846 cp++; 847 else 848 error("missing %c/n", q); 849 } while (q == '"' && getchr() == '"'); // there is an '/"' after the literal string, so apply string concetation 850 cl = put(0, cl); 851 if (n >= BUFSIZE) 852 error("%s literal too long/n", q == '"' ? "string" : "character"); 853 if (Aflag >= 2 && q == '"' && n > 509) 854 warning("more than 509 characters in a string literal/n"); 855 if (Aflag >= 2 && nbad > 0) 856 warning("%s literal contains non-portable characters/n", 857 q == '"' ? "string" : "character"); 858 return cl; 859 }
// comments on string literal DFA, in lex.c
156 int gettok(void) {
........
370 case '"': { 371 char *s = scon(*--cp, cput, cbuf); // s points to cbuf[] or wcbuf[] 372 tval.type = array(chartype, s - cbuf, 0); // !! array(widechar, s - wcbuf, 0) for wide string literal 373 tval.u.c.v.p = cbuf; // !! no string copy (1) 374 tsym = &tval; 375 return SCON; 376 }
// comments on literal string expression, in expr.c
339 static Tree primary(void) { 340 Tree p; 341 342 assert(t != '('); 343 switch (t) { 344 case ICON:
....
348 case SCON: if (ischar(tsym->type->type)) // !!! for ASCII character, tsym->type is a "char" 349 tsym->u.c.v.p = stringn(tsym->u.c.v.p, tsym->type->size); // !!! string copy here (2) 350 else // !!! wide string character, tsym->type is a "widechar " 351 tsym->u.c.v.p = memcpy(allocate(tsym->type->size, PERM), tsym->u.c.v.p, tsym->type-> size); 352 tsym = constant(tsym->type, tsym->u.c.v); 353 if (tsym->u.c.loc == NULL) 354 tsym->u.c.loc = genident(STATIC, tsym->type, GLOBAL); 355 p = idtree(tsym->u.c.loc); break;
[1] invalid definition in c, but valid in c++, no error reported because afte c-preprocessor, it's become "hello /tworld"
