CODEWITHSUNDEEP
clexflex-lexer
John Roberts
John Roberts

Reputation: 5966

Flex: Use Text File as Input Stream

So I've used flex to generate a c file from my lex code, and then used gcc to create the corresponding actual parser .exe. However, I can't figure out how to get it to read from anything other than my own typed input. I am trying to get it to parse a huge dictionary file. Can anyone help?

Upvotes: 8

Views: 19039

Answers (4)

GDBxNS
GDBxNS

Reputation: 449

In UBUNTU Position terminal in folder where is .l file then type following:

flex nameOfFile.l

then

gcc lex.yy.c

then ./a.out <nameOfFileYouWantToPass.extension (eg. ./a.out <test.txt)

.l file and test.txt should be in same folder

Upvotes: -1

Some programmer dude
Some programmer dude

Reputation: 409216

You have two ways of solving it. The first is to redirect input from standard input with the command prompt < operation:

> parser.exe < some_file.txt

The other solution is to let the program open the file, and tell the lexer what the file is. For more information about it see the Flex manual. The important functions are yy_create_buffer and yy_switch_to_buffer.

Upvotes: 13

forumulator
forumulator

Reputation: 875

Adding onto the above answer by @Eliko, while using flex with yacc/bison, you can define FILE *yyin; in the global part of your grammar.y file. The definition in the generated lex.yy.c is an extern FILE *yyin by default. Thus, in your grammar.y, do something like this:

/* Some other global definitions */
FILE *yyin;
%%
/* Grammar rules*/
/* Grammar rules*/
%%
void main(int argc, char **argv) {
  /* Process command line args*/
  yyin = fopen("input.c", "r");
  yyparse();
  fclose(yyin);
  return 0;
}

Upvotes: 8

jiasli
jiasli

Reputation: 9128

Try to add the following code to your *.l file.

int main(int argc, char *argv[])
{
    yyin = fopen(argv[1], "r");
    yylex();
    fclose(yyin);
}

Upvotes: 13

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