编译原理第六章上机辅导.pptVIP

* 3.3 语法分析器 table:IDENTIFIER { $$=$1; }; fieldsdefinition:field_type { $$=$1; cfdef_end=$1; } |fieldsdefinition , field_type { $$=$1; cfdef_end-next_fdef=$3; cfdef_end=$3; }; * 3.3 语法分析器 field_type:field type { $$=(_createfieldsdef_type *)malloc( sizeof(_createfieldsdef_type)); $$-field=$1; if (strlen($2)==0) /*表示类型为int的时候，用INT表示类型，长度定为4*/ { $$-type=INT; $$-length=4; $$-next_fdef=NULL; } * 3.3 语法分析器 else /*类型为CHAR：用CHAR表示类型，长度定为$2*/ {$$-type=CHAR; $$-length=atoi($2); $$-next_fdef=NULL; } }; field:IDENTIFIER { $$=$1; }; type: CHAR ( NUMBER ) {$$=$3;} |INT {$$=\0;}; * 3.4 SELECT 语句的实现 词法分析部分： SELECT {return SELECT;} FROM {return FROM;} WHERE {return WHERE;} AND {return AND;} OR {return OR;} ; | ( | ) | , | | \. | = | | {return yytext[0];} * 3.4 SELECT 语句的实现 1.设计SELECT语言文法 select 语句文法： statement→selectsql | ...... selectsql→SELECT fields_star FROM tables ; | SELECT fields_star FROM tables WHERE conditions ; fields_star→table_fields | * tables→table | tables , table table_fields→table_field | table_fields , table_field table_field→field | table . field table → IDENTIFIER field → IDENTIFIER * 3.4 SELECT 语句的实现 设计语法树的节点，用于存放表达式的语法树； typedef struct _selectedfields{ /*select语句中选中的字段*/ char *table; char *field; struct _selectedfields *next_sf; }_selectedfields_type; typedef struct _selectedtables{ /*select语句中选中的表*/ char *table; struct _selectedtables *next_st; }_selectedtables_type; typedef struct _selectstruct{ /*select语法树的根节点*/ _selectedfields_type *sf; _selectedtables_type *st; _conditions_type *cons; }_selectstruct_type; * 3.4 SELECT 语句的实现 typedef struct _conditions{ struct _conditions *left; struct _conditions *right; char comp_op; /*(a--and),(o--or), , , = */ char type; /*2--是表的字段，1--是字符串型，0--是整型*/ char *table; /*不为NULL就存放表名*/ char *value;