next

/* return next token with macro substitution */
ST_FUNC void next(void)
{
    Sym *nested_list, *s;
    TokenString str;
    struct macro_level *ml = 0;

 redo:
    if (parse_flags & PARSE_FLAG_SPACES)
        next_nomacro_spc();
    else
        next_nomacro();
    if (!macro_ptr) {
        //macro_ptr为空表明, 是直接从源码中读到的，而不是宏替换后的
        //可能需要进行宏替换
        /* if not reading from macro substituted string, then try
           to substitute macros */
        if (tok >= TOK_IDENT &&
            (parse_flags & PARSE_FLAG_PREPROCESS)) {
            //如果tok是宏, table_ident[tok-TOK_IDENT]->sym_define
            //将记录它到底被定义成什么tok序列了
            //tcc_define_symbol
            //parse_define
            //define_push

            // 例子;
            // #define s ss
            // #define tt ttt
            // #define t tt
            // #define t1 t2
            // #define b(x) t + t1
            // #define a(d) d + s
            // a(b(x));


            s = define_find(tok);
            if (s) {
                //a 是宏
                /* we have a macro: we try to substitute */
                tok_str_new(&str);
                nested_list = NULL;
                ml = NULL;
                //进行替换, tok序列保存在str中, 结果由macro_ptr保存
                if (macro_subst_tok(&str, &nested_list, s, &ml) == 0) {
                    /* substitution done, NOTE: maybe empty */
                    tok_str_add(&str, 0);
                    macro_ptr = str.str;
                    macro_ptr_allocated = str.str;
                    goto redo;
                }
            }
        }
    } else {
        if (tok == 0) {
            /* end of macro or end of unget buffer */
            if (unget_buffer_enabled) {
                macro_ptr = unget_saved_macro_ptr;
                unget_buffer_enabled = 0;
            } else {
                /* end of macro string: free it */
                tok_str_free(macro_ptr_allocated);
                macro_ptr_allocated = NULL;
                macro_ptr = NULL;
            }
            goto redo;
        } else if (tok == TOK_NOSUBST) {
            /* discard preprocessor's nosubst markers */
            goto redo;
        }
    }

    /* convert preprocessor tokens into C tokens */
    if (tok == TOK_PPNUM &&
        (parse_flags & PARSE_FLAG_TOK_NUM)) {
        parse_number((char *)tokc.cstr->data);
    }
}