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source code of scanf

Discussion in 'C' started by gyanu, Jan 31, 2008.

  1. gyanu

    gyanu New Member

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    I want to create a new function myscanf (char *format,...) which does same as scanf() without using any library function other than getchar().
    Pls soomeone get it done for meeeeee.plssssssssssss
     
  2. shabbir

    shabbir Administrator Staff Member

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    Code:
    char c;
    do 
    {
        c=getchar();
        putchar (c);
    } while (c != '\n');
     
  3. asadullah.ansari

    asadullah.ansari TechCake

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    You are still using library function getchar() and putchar().

    He is asking if i am correct.


    Code:
    #include "stddef.h"
    #include "stdarg.h"
    #include "stdlib.h"
    
    extern FILE *Stderr;
    
    
    int  MyScanf(char *s, const char *fmt, ...)
    {
    	char *s0;
    	va_list ap;
    	long L, *Lp;
    	int i, *ip, rc = 0;
    	va_start(ap, fmt);
    	for( ; ; ) {
    		for(;;) {
    			switch(i = *(unsigned char *)fmt++) {
    				case 0:
    					goto done;
    				case '%':
    					break;
    				default:
    					if (i <= ' ') {
    						while(*s <= ' ')
    							if (!*s++)
    								return rc;
    						}
    					else if (*s++ != i)
    						return rc;
    					continue;
    				}
    			break;
    			}
    		switch(*fmt++) {
    			case 'l':
    				if (*fmt != 'd')
    					bad(fmt);
    				fmt++;
    				Lp = va_arg(ap, long*);
    				L = strtol(s0 = s, &s, 10);
    				if (s > s0) {
    					rc++;
    					*Lp = L;
    					continue;
    					}
    				return rc;
    			case 'd':
    				ip = va_arg(ap, int*);
    				L = strtol(s0 = s, &s, 10);
    				if (s > s0) {
    					rc++;
    					*ip = (int)L;
    					continue;
    					}
    				return rc;
    			default:
    				bad(fmt);
    			}
    		}
     done:
    	return rc;
    	}
    	}
    
     
  4. asadullah.ansari

    asadullah.ansari TechCake

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    Oh!! At the last of code add one function

    va_end ( ap );
     
  5. gyanu

    gyanu New Member

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    Shabbir bhai, hi
    U have helped me really.......... But my problem is not about supporting integer but rather %s,for string datatype char buf[100]
    %x, for hexadecimal
    %c for characters
    please help me little bit more
     
  6. gyanu

    gyanu New Member

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    ansari bhai
    Thanks a lot .U r great but my problems are little more tough.I should not use myscanf(char *s,char *fmt,...)
    Also it should support %c,%x and %s for strings too
     
  7. shabbir

    shabbir Administrator Staff Member

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    I could not get you.
     
  8. oogabooga

    oogabooga New Member

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    Could we please see some of your code?
    I've seen this on another forum, and I've yet to see any code from you.
    People are not just going to do it for you (hopefully).
    If you want to cheat, look up some open source code for scanf.
     
  9. gyanu

    gyanu New Member

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    I have to create and implement a function myscanf(char *format,...) wilthout using any library functions other than getchar().
    My program would support to undersand---------myscanf("%d%s%x",a,b[],c);
     
  10. shabbir

    shabbir Administrator Staff Member

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    The string parsing and variable number of arguments in a function is all together a diiferent topic and you can check out - OutputDebugString with variable number of arguments for that but I guess your initial requirement is fully satisfied with the code snippet I provided.
     
  11. asadullah.ansari

    asadullah.ansari TechCake

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    Really i am unable to understand what's your requirement!!!
     
  12. imrantechi

    imrantechi New Member

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    i feel this code is really self explanatary ,

    you can explain well
     
  13. gyanu

    gyanu New Member

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    //please try to sort out the errors
    //I ve tried to make the function but has too much errors........
    //pls do it ....
    Code:
    #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);
    }
     
    Last edited by a moderator: Feb 13, 2008

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