Question

我要写的不是

identifier      [a-zA-Z0-9]+

为了接受仅由数字完成的字符串？

我写了新的野牛和flex文件，以便明确我的问题。野牛档案：

%{
#include <stdio.h>
#include <string>
using namespace std;
extern int yylex();
extern void yyerror(char*);
%}

//Symbols
%union
{
    double double_val;
    char *str_val;
};

%token START
%token STOP
%token BEGIN_NUM
%token END_NUM
%token BEGIN_STRING
%token END_STRING

%token <double_val> NUMBER
%token <str_val>    IDENTIFIER

%start MyTest

%%

MyTest:
    START Block STOP
    ;

Block:
    /* empty */
    | Block BEGIN_STRING IDENTIFIER END_STRING { printf("received string: %s \n", $3); }
    | Block BEGIN_NUM NUMBER END_NUM { printf("received number: %f \n", $3); }
    ;

%%

Flex文件：

%{
#include <string>
#include "test.tab.h"
void yyerror(char*);
int yyparse(void);
%}
blanks          [ \t\n]+
identifier      [a-zA-Z0-9]+
number          [0-9][0-9]*(.[0-9]+)?
%%

{blanks}        { /* ignore */ };

"<test>"        return(START);
"</test>"   return(STOP);
"<string>"      return(BEGIN_STRING);
"</string>"     return(END_STRING);
"<num>"     return(BEGIN_NUM);
"</num>"        return(END_NUM);

{number}        { yylval.double_val = atof(yytext);
                  return(NUMBER);
                }
{identifier}    { 
                  yylval.str_val=strdup(yytext);
                  return(IDENTIFIER);
                }

%%

void yyerror (char* str){ printf (" ERROR : Could not parse! %s\n", str );}
int yywrap (void){ }
int main(int num_args, char** args){
    if(num_args != 2) {printf("usage: ./parser filename\n"); exit(0);}
    FILE* file = fopen(args[1],"r");
    if(file == NULL) {printf("couldn't open %s\n",args[1]); exit(0);}
    yyin = file;
    yyparse();
    fclose(file);
}

当我输入此文件时，一切正常：

<test>
<num>1</num>
<string>eeeeee</string>
<num>2</num>
<string>cccc</string>
<num>3</num>
<num>4</num>
<string>asaa</string>
<string>dsa</string>
</test>

但是如果我用一个只有数字的值改变一个字符串字段：

<string>323</string>

我收到语法错误...

Answer 1

只有数字的字符串会返回令牌public class AppSettings extends PreferenceActivity { public static MultiSelectListPreference blocked; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); blocked = new MultiSelectListPreference(this); getFragmentManager().beginTransaction().replace(android.R.id.content, new PrefFrag()).commit(); } public static class PrefFrag extends PreferenceFragment { @Override public void onCreate(final Bundle savedInstanceState) { super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.preferences); MultiSelectListPreference blocked = (MultiSelectListPreference)findPreference("markedApps"); if (blocked == null) Log.e("NullPointerException", "Blocked is null"); AppSelector.populateAppList(); CharSequence[] appNames = new CharSequence[AppSelector.Data.appNames.size()]; CharSequence[] allApps = new CharSequence[AppSelector.Data.allApps.size()]; int i = 0; for (String appName : AppSelector.Data.appNames) appNames[i++] = (CharSequence) appName; i = 0; for (String app : AppSelector.Data.allApps) allApps[i++] = (CharSequence) app; blocked.setEntries(appNames); blocked.setEntryValues(allApps); } } }，因此您可以添加规则：

$(document).on('click', "#backClick", function (e) {
     //go back a page
     parent.history.back();

});

另外，让你的词法分析者只返回function bestComb(nums, target) { var combinations = []; var sums = []; function loop(idx, comb, sum) { if(idx >= nums.length || sum + nums[idx] > target) { combinations.push(comb.slice()); sums.push(sum); return; } for(var i = idx; i < nums.length; i++) { if(sum + nums[i] > target) break; if(sum + nums[i] === target) { combinations.push(comb.slice()); combinations[combinations.length - 1].push(nums[i]); sums.push(sum + nums[i]); break; } comb.push(nums[i]); loop(i + 1, comb, sum + nums[i]); comb.pop(); } } nums = nums.slice(); nums.sort(function(a,b) {return a - b}); loop(0, [], 0); if(sums.length === 0) return null; var maxSum = sums[0], maxComb = combinations[0]; for(var i = 1; i < sums.length; i++) { if(sums[i] > maxSum || sums[i] === maxSum && combinations[i].length < maxComb.length) { maxSum = sums[i]; maxComb = combinations[i]; } } return maxComb; } var nums = [25, 60, 13, 48, 23, 29, 27, 22]; var solution = bestComb(nums, 90); console.log(solution); NUMBER以外的所有内容Block: Block BEGIN_STRING NUMBER END_STRING { printf("received number as string: %f \n", $3); }代币，并在任何地方使用它：

TEXT

此外，你的词法分析者应该有这样的规则：

或

最后。

如果没有这样的规则，输入中的奇数字符只会被回显到输出，这几乎肯定不是你想要的编译器（尽管对于只是对一些简单的文本处理器进行一些修改可能没问题。输入，并留下其余的作为传递）。您想要的取决于您希望如何处理错误 - 如果您的语法中没有错误恢复规则而只是想忽略额外的字符，那么前者很好，而如果您在语法中实现了错误恢复方案，后者将任何额外的字符作为单个标记提供给解析器，您的错误恢复可以使用它们做更聪明的事情。

Bison / Flex字符串令牌识别

1 个答案: