How create a FILE* from char * without create a temporary file

Question

I'm creating a program using lex and yacc to parse text, but i need create a parser of various content. I don't wish use the stdin, if i using FILE *yyin to specify the input, i can change the source. I need can call the function from library parse (created with lex file and yacc file) to parse this content and receive a result.

/**
* This i don't know is possible, receive a char * and return a FILE*
*/
FILE *function_parse_to_file(char* text){
    FILE *fp = NULL;
    /**
    * is really necessary create a temporary file with content text?
    */

    return fp
}
/**
* I need call from other library or application
*/
char *function_parse_from_lex(char* text){
    yyin = function_parse_to_file(text);
    init(); 
    yyparse(); 
    fclose(yyin); 
}

Is the `char*` a file name or the actual text you want to parse? — Code-Apprentice, Mar 13 '13 at 16:55
possible duplicate of [String input to flex lexer](http://stackoverflow.com/questions/780676/string-input-to-flex-lexer) — Code-Apprentice, Mar 13 '13 at 16:56

score 2 · Accepted Answer · answered Mar 13 '13 at 16:53

2

On a POSIX-2008-compliant system (and on Linux), you can use fmemopen to get a FILE* handle on an in-memory buffer.

answered Mar 13 '13 at 16:53

Fred Foo

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Simple and objective, is exactly what i needed. – Sileno Brito Mar 13 '13 at 17:11

score 1 · Answer 2 · answered Mar 13 '13 at 16:58

1

You can define YY_INPUT macro with three arguments: buffer, result, max_size, where:

buffer - input with buffer where to read data,
result - output to store number of bytes read
max_size - input with buffer size

Just include the macro definition in your Lex file using header or inline and it will be used instead of fread(...)

answered Mar 13 '13 at 16:58

Valeri Atamaniouk

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I did not know this option, thanks, was not exactly what I needed at that moment, but I think it will help me a lot in the future. – Sileno Brito Mar 13 '13 at 17:14

score 0 · Answer 3 · answered Mar 13 '13 at 17:00

You really haven't stated your question clearly, but I am going to assume you want to create a FILE * which will return the contents of the string pointed to by the char * when data is read from it. You could simply create a pipe and then invoke fdopen on the read side. It is a bit dangerous to just write the data into the write side, since the write might block and lead to a deadlock, but you can certainly fork a child and have the child write the data into the pipe.

On the other hand, there's no real reason not to create a temporary file. Assuming you are going to unlink the file after you read it, there's very little chance of the data ever going to disk (the OS will keep it in memory) If you're really concerned to can use a path on a ram disk.

How create a FILE* from char * without create a temporary file

3 Answers3