LEX & YACC 写的一个表达式计算程序

前两天觉得LEX和YACC挺强大的，稍微写了一个处理表达式的程序

 

LEX文件：

%{ #include <stdio.h> #include <string.h> #include "y.tab.h" extern char *yytext; %} %% [0-9]+ yylval.number = atoi(yytext); return NUMBER; /|/| yylval.string = strdup(yytext); return OPER13_LOGI_OR; && yylval.string = strdup(yytext); return OPER12_LOGI_AND; /| yylval.string = strdup(yytext); return OPER11_OR; /^ yylval.string = strdup(yytext); return OPER10_POWER; & yylval.string = strdup(yytext); return OPER9_AND; (==|!=) yylval.string = strdup(yytext); return OPER8_EQU; (<|>|<=|>=) yylval.string = strdup(yytext); return OPER7_BIGGER; [+-] yylval.string = strdup(yytext); return OPER5_ADD; [*/%] yylval.string = strdup(yytext); return OPER4_MUL; [!-] yylval.string = strdup(yytext); return OPER2_NOT; /( return BRACKETLEFT; /) return BRACKETRIGHT; [/n/r] return LINERETURN; [ /t]+ /* ignore */ %%

 

YACC文件：

%{ #include <stdio.h> #include <string.h> extern char *yytext; void yyerror(const char* str) { fprintf(stderr, "error: %s/n", str); } int yywrap() { return 1; } main() { yyparse(); } %} %token BRACKETLEFT BRACKETRIGHT LINERETURN %union { int number; char* string; } %token <number> NUMBER %token <string> OPER13_LOGI_OR %token <string> OPER12_LOGI_AND %token <string> OPER11_OR %token <string> OPER10_POWER %token <string> OPER9_AND %token <string> OPER8_EQU %token <string> OPER7_BIGGER %token <string> OPER5_ADD %token <string> OPER4_MUL %token <string> OPER2_NOT %type <number> expr %type <number> expr12 %type <number> expr11 %type <number> expr10 %type <number> expr9 %type <number> expr8 %type <number> expr7 %type <number> expr5 %type <number> expr4 %type <number> expr2 %type <number> expr1 %% lines : lines expr LINERETURN { printf("result: %d/n", $2);} | lines LINERETURN | error { yyerror("line error:");} ; expr : expr OPER13_LOGI_OR expr12 { $$ = $1 || $3;} | expr12 ; expr12 : expr12 OPER12_LOGI_AND expr11 { $$ = $1 && $3;} | expr11 ; expr11 : expr11 OPER11_OR expr10 { $$ = $1 | $3;} | expr10 ; expr10 : expr10 OPER10_POWER expr9 { $$ = $1 ^ $3;} | expr9 ; expr9 : expr9 OPER9_AND expr8 { $$ = $1 & $3;} | expr8 ; expr8 : expr8 OPER8_EQU expr7 { if ( strncmp($2, "==", 2) == 0) { $$ = $1 == $3; } else if (strncmp($2, "!=", 2) == 0) { $$ = $1 != $3; } } | expr7 ; expr7 : expr7 OPER7_BIGGER expr5 { if ( strncmp($2, "<=", 2) == 0) { $$ = $1 <= $3; } else if (strncmp($2, ">=", 2) == 0) { $$ = $1 >= $3; } else if (strncmp($2, "<", 1) == 0) { $$ = $1 < $3; } else if (strncmp($2, ">", 1) == 0) { $$ = $1 > $3; } } | expr5 ; expr5 : expr5 OPER5_ADD expr4 { if ( strncmp($2, "+", 1) == 0) { $$ = $1 + $3; } else if (strncmp($2, "-", 1) == 0) { $$ = $1 - $3; } } | expr4 ; expr4 : expr4 OPER4_MUL expr2 { if ( strncmp($2, "*", 1) == 0) { $$ = $1 * $3; } else if (strncmp($2, "/", 1) == 0) { $$ = $1 / $3; } else if (strncmp($2, "%", 1) == 0) { $$ = $1 % $3; } } | expr2 ; expr2 : OPER2_NOT expr2 { if ( strncmp($1, "!", 1) == 0) { $$ = !($2); } else if (strncmp($1, "-", 1) == 0) { $$ = -($2); } } | expr1 ; expr1 : BRACKETLEFT expr BRACKETRIGHT { $$ = $2; } | BRACKETLEFT expr error { $$ = $2; yyerror("missing ')'"); } | NUMBER ; %%

 

编译并运行：

lex expr.l  && yacc -d expr.y && gcc lex.yy.c y.tab.c -o expr -ll && echo "OK" && ./expr

 

 

附表达式的优先级表： 

http://www.cppreference.com/wiki/operator_precedence

 

Precedence	Operator	Description	Example	Overloadable	Associativity
1	::	Scope resolution operator	Class::age = 2;	no	none
2	() () [] -> . ++ -- const_cast dynamic_cast static_cast reinterpret_cast typeid	Function call Member initalization Array access Member access from a pointer Member access from an object Post-increment Post-decrement Special cast Special cast Special cast Special cast Runtime type information	isdigit('1') c_tor(int x, int y) : _x(x), _y(y*10){}; array[4] = 2; ptr->age = 34; obj.age = 34; for( int i = 0; i < 10; i++ ) cout << i; for( int i = 10; i > 0; i-- ) cout << i; const_cast<type_to>(type_from); dynamic_cast<type_to>(type_from); static_cast<type_to>(type_from); reinterpret_cast<type_to>(type_from); cout « typeid(type).name();	yes yes yes yes no yes yes no no no no no	left to right
3	! not ~ compl ++ -- - + * & new new [] delete delete [] (type) sizeof	Logical negation Alternate spelling for ! Bitwise complement Alternate spelling for ~ Pre-increment Pre-decrement Unary minus Unary plus Dereference Address of Dynamic memory allocation Dynamic memory allocation of array Deallocating the memory Deallocating the memory of array Cast to a given type Return size of an object or type	if( !done ) … flags = ~flags; for( i = 0; i < 10; ++i ) cout << i; for( i = 10; i > 0; --i ) cout << i; int i = -1; int i = +1; int data = *intPtr; int *intPtr = &data; long *pVar = new long; MyClass *ptr = new MyClass(args); delete pVar; delete [] array; int i = (int) floatNum;//int size = sizeof(float);	yes yes yes yes yes yes yes yes yes yes yes yes yes no	right to left
4	->* .*	Member pointer selector Member object selector	ptr->*var = 24; obj.*var = 24;	yes no	left to right
5	* / %	Multiplication Division Modulus	int i = 2 * 4; float f = 10.0 / 3.0; int rem = 4 % 3;	yes yes yes	left to right
6	+ -	Addition Subtraction	int i = 2 + 3; int i = 5 - 1;	yes yes	left to right
7	<< >>	Bitwise shift left Bitwise shift right	int flags = 33 << 1; int flags = 33 >> 1;	yes yes	left to right
8	< <= > >=	Comparison less-than Comparison less-than-or-equal-to Comparison greater-than Comparison greater-than-or-equal-to	if( i < 42 ) … if( i <= 42 ) ... if( i > 42 ) … if( i >= 42 ) ...	yes yes yes yes	left to right
9	== eq != not_eq	Comparison equal-to Alternate spelling for == Comparison not-equal-to Alternate spelling for !=	if( i == 42 ) ... if( i != 42 ) …	yes - yes	left to right
10	& bitand	Bitwise AND Alternate spelling for &	flags = flags & 42;	yes	left to right
11	^ xor	Bitwise exclusive OR (XOR) Alternate spelling for ^	flags = flags ^ 42;	yes	left to right
12	| bitor	Bitwise inclusive (normal) OR Alternate spelling for |	flags = flags | 42;	yes	left to right
13	&& and	Logical AND Alternate spelling for &&	if( conditionA && conditionB ) …	yes	left to right
14	|| or	Logical OR Alternate spelling for ||	if( conditionA || conditionB ) ...	yes	left to right
15	? :	Ternary conditional (if-then-else)	int i = (a > b) ? a : b;	no	right to left
16	= += -= *= /= %= &= and_eq ^= xor_eq |= or_eq <<= >>=	Assignment operator Increment and assign Decrement and assign Multiply and assign Divide and assign Modulo and assign Bitwise AND and assign Alternate spelling for &= Bitwise exclusive or (XOR) and assign Alternate spelling for ^= Bitwise normal OR and assign Alternate spelling for |= Bitwise shift left and assign Bitwise shift right and assign	int a = b; a += 3; b -= 4; a *= 5; a /= 2; a %= 3; flags &= new_flags; flags ^= new_flags; flags |= new_flags; flags <<= 2; flags >>= 2;	yes yes yes yes yes yes yes yes yes yes yes	right to left
17	throw	throw exception	throw EClass(“Message”);	no
18	,	Sequential evaluation operator	for( i = 0, j = 0; i < 10; i++, j++ ) …	yes	left to right