Implementing scanf with getchar

[gyanu]

//I tried to fix the errors but I failed.
//pls do it for me.......

#include<stdio.h>
#include<conio.h>
void main()
{
int a;
void scanchar(char**);
int scans(char**,char*,int,int);
int scani(char**,int,int,int,int,int,int);
int myscanf(char *);
int smyscanf(char*,char*);
clrscr();
printf("enter");
myscanf("%d",&a);
printf("%d",a);
getch();
}
static void scanchar(char **str)
{
 extern int getchar();
 if (str) {
  **str = getchar();
  ++(*str);
 }
 else (void)getchar();
}
#define PAD_RIGHT 1
#define PAD_ZERO 2
static int prints(char **in, const char *string, int width, int pad)
{
 register int sc = 0, padchar = ' ';
 if (width > 0) {
  register int len = 0;
  register const char *ptr;
  for (ptr = string; *ptr; ++ptr) ++len;
  if (len >= width) width = 0;
  else width -= len;
  if (pad & PAD_ZERO) padchar = '0';
 }
 if (!(pad & PAD_RIGHT)) {
  for ( ; width > 0; --width) {
   scanchar (in, padchar);
   ++sc;
  }
 }
 for ( ; *string ; ++string) {
  scanchar (in, *string);
  ++sc;
 }
 for ( ; width > 0; --width) {
  scanchar (in, padchar);
  ++sc;
 }
 return sc;
}
/* the following should be enough for 32 bit int */
#define SCAN_BUF_LEN 12
static int scani(char **in, int i, int b, int sg, int width, int pad, int letbase)
{
 char scan_buf[SCAN_BUF_LEN];
 register char *s;
 register int t, neg = 0, sc = 0;
 register unsigned int u = i;
 if (i == 0) {
  scan_buf[0] = '0';
  scan_buf[1] = '\0';
  return scans (out, print_buf, width, pad);
 }
 if (sg && b == 10 && i < 0) {
  neg = 1;
  u = -i;
 }
 s = scan_buf + SCAN_BUF_LEN-1;
 *s = '\0';
 while (u) {
  t = u % b;
  if( t >= 10 )
   t += letbase - '0' - 10;
  *--s = t + '0';
  u /= b;
 }
 if (neg) {
  if( width && (pad & PAD_ZERO) ) {
   scanchar (in,'-');
   ++sc;
   --width;
  }
  else {
   *--s = '-';
  }
 }
 return sc + scans (in, s, width, pad);
}
static int scan(char **in, int *varg)
{
 register int width, pad;
 register int sc = 0;
 register char *format = (char *)(*varg++);
 char scr[2];
 for (; *format != 0; ++format) {
  if (*format == '%') {
   ++format;
   width = pad = 0;
   if (*format == '\0') break;
   if (*format == '%') goto in;
   if (*format == '-') {
    ++format;
    pad = PAD_RIGHT;
   }
   while (*format == '0') {
    ++format;
    pad |= PAD_ZERO;
   }
   for ( ; *format >= '0' && *format <= '9'; ++format) {
    width *= 10;
    width += *format - '0';
   }
   if( *format == 's' ) {
    register char *s = *((char **)varg++);
    sc += scans (in, s?s:"(null)", width, pad);
    continue;
   }
   if( *format == 'd' ) {
    sc += scani (in, *varg++, 10, 1, width, pad, 'a');
    continue;
   }
   if( *format == 'x' ) {
    sc += scani (in, *varg++, 16, 0, width, pad, 'a');
    continue;
   }
   if( *format == 'X' ) {
    sc += scani (in, *varg++, 16, 0, width, pad, 'A');
    continue;
   }
   if( *format == 'u' ) {
    sc += scani (in, *varg++, 10, 0, width, pad, 'a');
    continue;
   }
   if( *format == 'c' ) {
    /* char are converted to int then pushed on the stack */
    scr[0] = *varg++;
    scr[1] = '\0';
    sc += scans (in, scr, width, pad);
    continue;
   }
  }
  else {
  in:
   scanchar (in, *format);
   ++sc;
  }
 }
 if (in) **in = '\0';
 return sc;
}
/* assuming sizeof(void *) == sizeof(int) */
int myscanf(const char *format, ...)
{
 register int *varg = (int *)(&format);
 return scan(0, varg);
}
int smyscanf(char *out, const char *format, ...)
{
 register int *varg = (int *)(&format);
 return scan(&out, varg);
}

[Jishnu]

Use code tags. Mention specific problems and the line no.s. The size of the code is a bit too lengthy. Proper formatting and specific questions would take you a long way ahead in getting help.

[Ancient Dragon]

what are a few of the error messages you got ? What compiler are you using ? My guess is that you did not write the code you posted because its too advanced for someone that asked the question you asked.

The code appears to have been written with Turbo C compiler ( clrscr() is only supported by Turbo C) so you will have to rewrite parts of that code that contains Borland-specific functions.

[Narue]

That looks like a healthy mix up of scanf and printf. Why are you trying to do padding in scanf? That code is actually quite awful, so you probably want to redesign and rewrite it. I get the impression that this isn't your code, so I'll give you a better example to start with:

#include <ctype.h>
#include <stdio.h>
#include <stdarg.h>

int myscanf ( const char *fmt, ... );
static int trim_leading ( void );
static int myscanf_internal ( const char *fmt, va_list args );

int main ( void )
{
  char s[100];
  int a;

  myscanf ( "%s%d", s, &a );
  printf ( "%s\n%d\n", s, a );

  return 0;
}

int myscanf ( const char *fmt, ... )
{
  va_list args;
  int rv;

  va_start ( args, fmt );
  rv = myscanf_internal ( fmt, args );
  va_end ( args );

  return rv;
}

static int trim_leading ( void )
{
  int ch;

  do {
    if ( ( ch = getchar() ) == EOF )
      break;
  } while ( isspace ( ch ) );

  ungetc ( ch, stdin );

  return ch;
}

static int myscanf_internal ( const char *fmt, va_list args )
{
  int converted = 0;

  while ( *fmt != '\0' ) {
    if ( *fmt++ == '%' ) {
      switch ( *fmt ) {
      case 's':
        {
          char *dst = va_arg ( args, char* );
          int ch;

          trim_leading();

          while ( ( ch = getchar() ) != EOF && !isspace ( ch ) )
            *dst++ = (char)ch;
          *dst = '\0';

          ++converted;
        }
        break;
      case 'd':
        {
          int neg = 0;
          int dst = 0;
          int ch;
          int i;

          trim_leading();

          for ( i = 0; ( ch = getchar() ) != EOF; i++ ) {
            if ( i == 0 && ( ch == '-' || ch == '+' ) ) {
              neg = ( ch == '-' );
              continue;
            }

            if ( !isdigit ( ch ) ) {
              ungetc ( ch, stdin );
              break;
            }

            dst = 10 * dst + ( ch - '0' );
          }

          if ( neg )
            dst = -dst;

          *va_arg ( args, int* ) = dst;
          ++converted;
        }
        break;
      }
    }
  }

  return converted;
}