Wei
Not looking at the standard right now, but the following is valid:
x = 1, 2, 3; // x gets 3
A test for the second case would be
x = 3;
y = 3 * x = 2;
This should be an error, because 3 * x is not an lvalue.
Does this compile with tcc? (don't know, the machine I am on doesn't
have the compiler).
On Sat, 2009-09-05 at 01:05 +0800, Wei wrote:
> Hi, TCC stackholders,
>
> I am tracing TCC's source codes, and find something I don't
> understand.
> What I don't understand is about the grammar.
>
> From the C89 or C99 standard:
>
> ======================================================================
> assignment_expression
> : lvalue assignment_operator assignment_expression
> | conditional_expression
> ;
> ======================================================================
>
> However, in TCC,
>
> ======================================================================
> static void gexpr(void)
> {
> while (1) {
> expr_eq();
> if (tok != ',')
> break;
> vpop();
> next();
> }
> }
> ======================================================================
>
> and expr_eq( ) seems to parse C conditional expression (ie, xxx ?
> xxx : xxx).
> It seems that it doesn't parse codes like "a = b = c = d = 4;".
>
> And in the C standard,
>
> ======================================================================
> multiplicative_expression
> : (cast_expression) ('*' cast_expression | '/' cast_expression | '%'
> cast_expression)*
> ;
> ======================================================================
>
> However, in TCC, the function to parse "multiplicative_expression" is
> expr_prod( ):
>
> ======================================================================
> static void expr_prod(void)
> {
> int t;
>
> uneq();
> while (tok == '*' || tok == '/' || tok == '%') {
> t = tok;
> next();
> uneq();
> gen_op(t);
> }
> }
> ======================================================================
>
> and uneq( ) seems to parse the so-call "assignment_expression.", not
> the standard-defined "cast_expression"
>
> Why TCC uses such a grammar? it seems not compatible with the C
> standard.
>
> Wei.
>
>
>
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