String input to flex lexer

See this section of Flex's manual for information on how to scan in-memory buffers, such as strings.

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();
}

flex can parse char * using any one of three functions: yy_scan_string(), yy_scan_buffer(), and yy_scan_bytes() (see the documentation). Here's an example of the first:

typedef struct yy_buffer_state * YY_BUFFER_STATE;
extern int yyparse();
extern YY_BUFFER_STATE yy_scan_string(char * str);
extern void yy_delete_buffer(YY_BUFFER_STATE buffer);

int main(){
    char string[] = "String to be parsed.";
    YY_BUFFER_STATE buffer = yy_scan_string(string);
    yyparse();
    yy_delete_buffer(buffer);
    return 0;
}

The equivalent statements for yy_scan_buffer() (which requires a doubly null-terminated string):

char string[] = "String to be parsed.\0";
YY_BUFFER_STATE buffer = yy_scan_buffer(string, sizeof(string));

My answer reiterates some of the information provided by @dfa and @jlholland, but neither of their answers' code seemed to be working for me.

Here is what I needed to do :

extern yy_buffer_state;
typedef yy_buffer_state *YY_BUFFER_STATE;
extern int yyparse();
extern YY_BUFFER_STATE yy_scan_buffer(char *, size_t);

int main(int argc, char** argv) {

  char tstr[] = "line i want to parse\n\0\0";
  // note yy_scan_buffer is is looking for a double null string
  yy_scan_buffer(tstr, sizeof(tstr));
  yy_parse();
  return 0;
}

you cannot extern the typedef, which make sense when you think about it.