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我正在编写一个程序,该程序一次读取输入一个字符并确定它是十进制、八进制还是十六进制并将其转换为十进制以进行输出。那部分有效,问题是我while((ch=getchar()) != EOF)用来浏览文本,但 while 循环永远不会终止。听说EOF相当于-1,使用EOF的方法是control+z结束程序,但我希望它是自动的。我一直在使用标准输入以及为其提供 .txt 文本,并且程序不会终止的两种方式。我想知道是否有人可以查看我的代码并查看我哪里出错了。

(很长,对不起,我只是不知道这是否是我在案件中所做的事情)

int main (void) 
{
    int ch, chVal, decVal ;

    ch=getchar() ;

    while ((ch != EOF)) 
    {
        switch ( ch ) 
        {
            case ' ' :
                /* Just read until it’s not a space */
                while( ( ch == SPACE ) || ( ch== EOL ) ) 
                        ch=getchar();


            case '0' :
                /* integer, octal or hex possibilities */
                ch=getchar() ;

                /**** HEX ****/

                if ( ( ch=='x' ) || ( ch=='X' ) ) 
                {
                    /* potential hex. So far we have read in 0x.  We need to see what's next. */                
                    ch=getchar() ;

                    if ( ch== SPACE ) 
                    {
                        /* all we had was 0x entered */
                        outputIllegalToken() ;
                        break ; /* we need to end every pass through the switch with a space char (space, eoln or eof) */
                    }

                    decVal=0 ;
                    while ( ( ( '0' <= ch ) && ( ch <= '9' ) ) || ( ( 'a' <= ch ) && ( ch <= 'f' ) ) || ( 'A' <= ch ) && ( ch <= 'F' ) ) 
                    {
                        chVal = DecToHex( ch ) ;
                        decVal*=16 ;
                        decVal+=chVal ;
                        ch=getchar() ;
                    }

                    /* ch is no longer a hex val. */
                    if ( ch == SPACE || ch == EOL || ch == EOF ) 
                    {
                        /* All is good. */
                        outputHex( decVal );
                    } 
                    else 
                    {
                        if ( ch=='l' || ch=='L' ) 
                        {
                            ch=getchar() ;
                            if (( ch== SPACE ) || ( ch== EOL ) || ( ch==EOF )) 
                            {
                                outputLongHex( decVal ) ;
                            } 
                            else 
                            {
                                outputIllegalToken() ;
                                while ( ch!= SPACE && ch!= EOL && ch!= EOF ) 
                                { 
                                        getchar();
                                }
                            }
                        } 
                        else 
                        {
                            outputIllegalToken() ;
                            ch = getchar() ;
                            while ( ( ch!= SPACE ) && ( ch!= EOL ) && ( ch!= EOF ) ) 
                            { 
                                ch=getchar(); 
                            }
                        }
                    }
                    printf("do we come here? \n");
                    count++;
                     break;
                    /* end of the 0x scenario  ch is  a space char */
                }

               /****** 0 *******/

                if ( ch==' ' ) 
                {
                    /* just a 0 */
                    outputDecimal(0);
                    count++;
                    break ; /* end of 0 alone scenario. ch is a space */
                }

                /***** 0L ******/

                if ( ch=='l' || ch=='L' ) {
                    /* if there is space after the l, it's ok. otherwise illegal. */
                    ch=getchar() ;
                    if ( ( ch== SPACE ) || ( ch== EOL ) || (ch==EOF ) ) 
                    {
                        outputLongDecimal(0);
                    } 
                    else 
                    {
                        outputIllegalToken() ;
                        /* read to the next space */
                        ch=getchar() ;
                        while ( ( ch!= SPACE ) && ( ch!= EOL ) & ( ch!=EOF ) ) 
                                { 
                                ch=getchar(); 
                                }
                    }
                    count++;
                    break ;  /* end of 0L scenario.  ch is a space char. */
                }

                /**** Octal ****/

                if ( ( '0'<=ch )&&( ch<='7' ) ) 
                {
                    /* potentially octal  */
                    chVal=DecToHex( ch ) ;
                    decVal=chVal ;
                    ch=getchar() ;
                    while ( ( '0'<=ch )&&( ch<='7' ) ) 
                    {
                        decVal*=8 ;
                        decVal+=DecToHex( ch ) ;
                        ch=getchar() ;
                    }
                    /* no longer octal ch */
                    if ( ch== SPACE || ch== EOL || ch==EOF ) 
                    {
                        outputOctal( decVal ) ;

                    } 
                   else 
                    {
                        if ( ch=='l' || ch=='L' ) 
                        {
                            ch=getchar() ;
                            if (( ch== SPACE ) || ( ch== EOL ) || ( ch==EOF )) 
                            {
                                outputLongOctal(decVal) ;
                            } 
                            else 
                            {
                                outputIllegalToken() ;
                                while ( ch!= SPACE && ch!= EOL && ch!=EOF ) 
                                { 
                                        getchar();
                                }
                            }
                        } 
                        else 
                        {
                            outputIllegalToken() ;
                            ch = getchar() ;
                            while ( ( ch!= SPACE ) && ( ch!= EOL ) && ( ch!=EOF ) ) 
                            { 
                                ch=getchar(); 
                            }
                        }
                    count++;
                    break;/* end octal scenario  ch is a space character. */
                }

                count++;
                break ;

            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                /* potential decimal input */

                chVal=DecToHex( ch ) ;  /* convert the character to a number */
                decVal=chVal ;          /* keep track of the overall number */

                ch=getchar() ;
                while ( ( '0'<=ch ) && ( ch<='9' ) ) 
                {
                    chVal=DecToHex( ch ) ;
                    decVal*=10 ;
                    decVal+=chVal ;
                    ch=getchar() ;
                }

                /* integers have ended.  spaces or l is acceptable. everything else is illegal */
                if ( ( ch== SPACE ) || ( ch== EOL ) || ( ch==EOF )) 
                {
                    outputDecimal( decVal ) ;
                } 
                else if ( ( ch=='l' ) || ( ch=='L' ) ) 
                {
                    /* next char needs to be space in order to be a valid long integer */
                    ch==getchar() ;
                    if ( ( ch== SPACE ) || ( ch== EOL ) || ( ch==EOF ) ) 
                    {
                        outputLongDecimal( decVal ) ;
                    } 
                    else 
                    {
                        outputIllegalToken() ;
                        while ( ( ch!= SPACE) && ( ch!= EOL ) && ( ch!=EOF ) ) 
                        {
                            ch=getchar();
                        }
                    }
                }
                count++;
                break;
        }
    }
}

return 0;
}
4

2 回答 2

0

这是一个词法分析器。如果您使用flex/lex,它将是一个更容易编写和维护的程序,而不是重建这个复杂的轮子。这是一个灵活的十六进制转换器,八进制从零开始,以及其他所有内容的传递:

%{

%}
%option 8bit outfile="scanner.c"
%option nounput nomain noyywrap
%option warn

%%

0x[0-9]+ { fprinf(yyout, "%d", yytext); /* hex conversion */ }
0[0-9]+  { fprintf(yyout, "%d", yytext); /* octal conversion */ }
.|\n { ECHO; /* print everything else out unmodified */ }

%%
int main(int argc, char **argv);

int main (argc,argv)
int argc;
char **argv;
{
yylex();
return 0;
}

只需编译:

flex -Cf scanner.l 
gcc -O -o wordConverter scanner.c

它接受标准输入上的输入并输出直到 EOF。

于 2013-02-04T18:14:28.770 回答
0

这个:

            while( ( ch == SPACE ) || ( ch== EOL ) ) 
                    ch=getchar();

如果输入中的最后一个字符是空格,将导致无限循环。我认为您的意思是 simple ( ch == SPACE ),但是用 just 替换整个语句break;也可以。

可能还有其他错误...

于 2013-02-04T18:01:19.537 回答