What can I use for input conversion instead of scanf?

Question

I have very frequently seen people discouraging others from using scanf and saying that there are better alternatives. However, all I end up seeing is either

Answer 1

Here is an example of using flex to scan a simple input, in this case a file of ASCII floating point numbers that might be in either US (n,nnn.dd) or European (n.nnn,dd) formats. This is just copied from a much larger program, so there may be some unresolved references:

/* This scanner reads a file of numbers, expecting one number per line.  It  */
/* allows for the use of European-style comma as decimal point.              */

%{
  #include 
  #include 
  #include 
  #ifdef WINDOWS
    #include 
  #endif
  #include "Point.h"

  #define YY_NO_UNPUT
  #define YY_DECL int f_lex (double *val)

  double atofEuro (char *);
%}

%option prefix="f_"
%option nounput
%option noinput

EURONUM [-+]?[0-9]*[,]?[0-9]+([eE][+-]?[0-9]+)?
NUMBER  [-+]?[0-9]*[\.]?[0-9]+([eE][+-]?[0-9]+)?
WS      [ \t\x0d]

%%

[!@#%&*/].*\n

^{WS}*{EURONUM}{WS}*  { *val = atofEuro (yytext); return (1); }
^{WS}*{NUMBER}{WS}*   { *val = atof (yytext); return (1); }

[\n]
.


%%

/*------------------------------------------------------------------------*/

int scan_f (FILE *in, double *vals, int max)
{
  double *val;
  int npts, rc;

  f_in = in;
  val  = vals;
  npts = 0;
  while (npts < max)
  {
    rc = f_lex (val);

    if (rc == 0)
      break;
    npts++;
    val++;
  }

  return (npts);
}

/*------------------------------------------------------------------------*/

int f_wrap ()
{
  return (1);
}