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84 lines
3.2 KiB
C++
84 lines
3.2 KiB
C++
/* re2c lesson 001_upn_calculator, calc_001, (c) M. Boerger 2006 - 2007 */
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/*!ignore:re2c
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- basic interface for string reading
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. We define the macros YYCTYPE, YYCURSOR, YYLIMIT, YYMARKER, YYFILL
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. YYCTYPE is the type re2c operates on or in other words the type that
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it generates code for. While it is not a big difference when we were
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using 'unsigned char' here we would need to run re2c with option -w
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to fully support types with sieof() > 1.
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. YYCURSOR is used internally and holds the current scanner position. In
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expression handlers, the code blocks after re2c expressions, this can be
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used to identify the end of the token.
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. YYMARKER is not always being used so we set an initial value to avoid
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a compiler warning. Here we could also omit it compleley.
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. YYLIMIT stores the end of the input. Unfortunatley we have to use strlen()
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in this lesson. In the next example we see one way to get rid of it.
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. We use a 'for(;;)'-loop around the scanner block. We could have used a
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'while(1)'-loop instead but some compilers generate a warning for it.
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. To make the output more readable we use 're2c:indent:top' scanner
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configuration that configures re2c to prepend a single tab (the default)
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to the beginning of each output line.
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. The following lines are expressions and for each expression we output the
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token name and continue the scanner loop.
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. The second last token detects the end of our input, the terminating zero in
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our input string. In other scanners detecting the end of input may vary.
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For example binary code may contain \0 as valid input.
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. The last expression accepts any input character. It tells re2c to accept
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the opposit of the empty range. This includes numbers and our tokens but
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as re2c goes from top to botton when evaluating the expressions this is no
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problem.
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. The first three rules show that re2c actually prioritizes the expressions
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from top to bottom. Octal number require a starting "0" and the actual
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number. Normal numbers start with a digit greater 0. And zero is finally a
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special case. A single "0" is detected by the last rule of this set. And
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valid ocal number is already being detected by the first rule. This even
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includes multi "0" sequences that in octal notation also means zero.
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Another way would be to only use two rules:
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"0" [0-9]+
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"0" | ( [1-9] [0-9]* )
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A full description of re2c rule syntax can be found in the manual.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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int scan(char *s, int l)
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{
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char *p = s;
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char *q = 0;
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#define YYCTYPE char
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#define YYCURSOR p
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#define YYLIMIT (s+l)
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#define YYMARKER q
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#define YYFILL(n)
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for(;;)
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{
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/*!re2c
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re2c:indent:top = 2;
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"0"[0-9]+ { printf("Oct\n"); continue; }
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[1-9][0-9]* { printf("Num\n"); continue; }
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"0" { printf("Num\n"); continue; }
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"+" { printf("+\n"); continue; }
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"-" { printf("-\n"); continue; }
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"\000" { printf("EOF\n"); return 0; }
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[^] { printf("ERR\n"); return 1; }
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*/
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}
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}
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int main(int argc, char **argv)
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{
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if (argc > 1)
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{
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return scan(argv[1], strlen(argv[1]));
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}
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else
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{
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fprintf(stderr, "%s <expr>\n", argv[0]);
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return 1;
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}
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}
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