String input to flex lexer

Question

I want to create a read-eval-print loop using flex/bison parser. Trouble is, the flex generated lexer wants input of type FILE* and i would like it to be char*. Is there an

Answer 1

There's this funny code in libmatheval:

/* Redefine macro to redirect scanner input from string instead of
 * standard input.  */
#define YY_INPUT( buffer, result, max_size ) \
{ result = input_from_string (buffer, max_size); }

Answer 2

The following routines are available for setting up input buffers for scanning in-memory strings instead of files (as yy_create_buffer does):

• YY_BUFFER_STATE yy_scan_string(const char *str): scans a NUL-terminated string`
• YY_BUFFER_STATE yy_scan_bytes(const char *bytes, int len): scans len bytes (including possibly NULs) starting at location bytes

Note that both of these functions create, return a corresponding YY_BUFFER_STATE handle (which you must delete with yy_delete_buffer() when done with it) so yylex() scan a copy of the string or bytes. This behavior may be desirable since yylex() modifies the contents of the buffer it is scanning).

If you want avoid the copy (and yy_delete_buffer) using:

• YY_BUFFER_STATE yy_scan_buffer(char *base, yy_size_t size)

sample main:

int main() {
    yy_scan_buffer("a test string");
    yylex();
}