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 operatorClass::age = 2;nonone2()
()
[]
->
.
++
--
const_cast
dynamic_cast
static_cast
reinterpret_cast
typeidFunction 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 informationisdigit('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
noleft to right3!
not
~
compl
++
--
-
+
*
&
new
new []
delete
delete []
(type)
sizeofLogical 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 typeif( !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
noright to left4->*
.*Member pointer selector
Member object selectorptr->*var = 24;
obj.*var = 24;yes
noleft to right5*
/
%Multiplication
Division
Modulusint i = 2 * 4;
float f = 10.0 / 3.0;
int rem = 4 % 3;yes
yes
yesleft to right6+
-Addition
Subtractionint i = 2 + 3;
int i = 5 - 1;yes
yesleft to right7<<
>>Bitwise shift left
Bitwise shift rightint flags = 33 << 1;
int flags = 33 >> 1;yes
yesleft to right8<
<=
>
>=Comparison less-than
Comparison less-than-or-equal-to
Comparison greater-than
Comparison greater-than-or-equal-toif( i < 42 ) …
if( i <= 42 ) ...
if( i > 42 ) …
if( i >= 42 ) ...yes
yes
yes
yesleft to right9==
eq
!=
not_eqComparison equal-to
Alternate spelling for ==
Comparison not-equal-to
Alternate spelling for != if( i == 42 ) ...

if( i != 42 ) …
yes
-
yes
left to right10&
bitandBitwise AND
Alternate spelling for & flags = flags & 42;
yes
left to right11^
xorBitwise exclusive OR (XOR)
Alternate spelling for ^ flags = flags ^ 42;
yes
left to right12|
bitorBitwise inclusive (normal) OR
Alternate spelling for |flags = flags | 42;
yes
left to right13&&
andLogical AND
Alternate spelling for && if( conditionA && conditionB ) …
yes
left to right14||
orLogical OR
Alternate spelling for ||if( conditionA || conditionB ) ...
yes
left to right15? :Ternary conditional (if-then-else)int i = (a > b) ? a : b;noright to left16=
+=
-=
*=
/=
%=
&=
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 assignint 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
yesright to left17throwthrow exceptionthrow EClass(“Message”);no18,Sequential evaluation operatorfor( i = 0, j = 0; i < 10; i++, j++ ) …yesleft to right