explanation for source code of printf

[narendharg]

/*
 Copyright 2001, 2002 Georges Menie (<URL snipped>)
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.
    You should have received a copy of the GNU Lesser General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
/*
 putchar is the only external dependency for this file,
 if you have a working putchar, just remove the following
 define. If the function should be called something else,
 replace outbyte(c) by your own function call.
*/
#define putchar(c) outbyte(c)
static void printchar(char **str, int c)
{
 extern int putchar(int c);
 if (str) {
  **str = c;
  ++(*str);
 }
 else (void)putchar(c);
}
#define PAD_RIGHT 1
#define PAD_ZERO 2
static int prints(char **out, const char *string, int width, int pad)
{
 register int pc = 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) {
   printchar (out, padchar);
   ++pc;
  }
 }
 for ( ; *string ; ++string) {
  printchar (out, *string);
  ++pc;
 }
 for ( ; width > 0; --width) {
  printchar (out, padchar);
  ++pc;
 }
 return pc;
}
/* the following should be enough for 32 bit int */
#define PRINT_BUF_LEN 12
static int printi(char **out, int i, int b, int sg, int width, int pad, int letbase)
{
 char print_buf[PRINT_BUF_LEN];
 register char *s;
 register int t, neg = 0, pc = 0;
 register unsigned int u = i;
 if (i == 0) {
  print_buf[0] = '0';
  print_buf[1] = '\0';
  return prints (out, print_buf, width, pad);
 }
 if (sg && b == 10 && i < 0) {
  neg = 1;
  u = -i;
 }
 s = print_buf + PRINT_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) ) {
   printchar (out, '-');
   ++pc;
   --width;
  }
  else {
   *--s = '-';
  }
 }
 return pc + prints (out, s, width, pad);
}
static int print(char **out, int *varg)
{
 register int width, pad;
 register int pc = 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 out;
   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++);
    pc += prints (out, s?s:"(null)", width, pad);
    continue;
   }
   if( *format == 'd' ) {
    pc += printi (out, *varg++, 10, 1, width, pad, 'a');
    continue;
   }
   if( *format == 'x' ) {
    pc += printi (out, *varg++, 16, 0, width, pad, 'a');
    continue;
   }
   if( *format == 'X' ) {
    pc += printi (out, *varg++, 16, 0, width, pad, 'A');
    continue;
   }
   if( *format == 'u' ) {
    pc += printi (out, *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';
    pc += prints (out, scr, width, pad);
    continue;
   }
  }
  else {
  out:
   printchar (out, *format);
   ++pc;
  }
 }
 if (out) **out = '\0';
 return pc;
}
/* assuming sizeof(void *) == sizeof(int) */
int printf(const char *format, ...)
{
 register int *varg = (int *)(&format);
 return print(0, varg);
}
int sprintf(char *out, const char *format, ...)
{
 register int *varg = (int *)(&format);
 return print(&out, varg);
}
#ifdef TEST_PRINTF
int main(void)
{
 char *ptr = "Hello world!";
 char *np = 0;
 int i = 5;
 unsigned int bs = sizeof(int)*8;
 int mi;
 char buf[80];
 mi = (1 << (bs-1)) + 1;
 printf("%s\n", ptr);
 printf("printf test\n");
 printf("%s is null pointer\n", np);
 printf("%d = 5\n", i);
 printf("%d = - max int\n", mi);
 printf("char %c = 'a'\n", 'a');
 printf("hex %x = ff\n", 0xff);
 printf("hex %02x = 00\n", 0);
 printf("signed %d = unsigned %u = hex %x\n", -3, -3, -3);
 printf("%d %s(s)%", 0, "message");
 printf("\n");
 printf("%d %s(s) with %%\n", 0, "message");
 sprintf(buf, "justif: \"%-10s\"\n", "left"); printf("%s", buf);
 sprintf(buf, "justif: \"%10s\"\n", "right"); printf("%s", buf);
 sprintf(buf, " 3: %04d zero padded\n", 3); printf("%s", buf);
 sprintf(buf, " 3: %-4d left justif.\n", 3); printf("%s", buf);
 sprintf(buf, " 3: %4d right justif.\n", 3); printf("%s", buf);
 sprintf(buf, "-3: %04d zero padded\n", -3); printf("%s", buf);
 sprintf(buf, "-3: %-4d left justif.\n", -3); printf("%s", buf);
 sprintf(buf, "-3: %4d right justif.\n", -3); printf("%s", buf);
 return 0;
}

/*
* if you compile this file with
* gcc -Wall $(YOUR_C_OPTIONS) -DTEST_PRINTF -c printf.c
* you will get a normal warning:
* printf.c:214: warning: spurious trailing `%' in format
* this line is testing an invalid % at the end of the format string.
*
* this should display (on 32bit int machine) :
*
* Hello world!
* printf test
* (null) is null pointer
* 5 = 5
* -2147483647 = - max int
* char a = 'a'
* hex ff = ff
* hex 00 = 00
* signed -3 = unsigned 4294967293 = hex fffffffd
* 0 message(s)
* 0 message(s) with %
* justif: "left "
* justif: " right"
* 3: 0003 zero padded
* 3: 3 left justif.
* 3: 3 right justif.
* -3: -003 zero padded
* -3: -3 left justif.
* -3: -3 right justif.
*/
#endif

[Ancient Dragon]

now that you have posted all that code, what, if anything, is your question?

[narendharg]

Normally we use printf to print a statement in C-Language,but how can we print a statement without using a printf in LINUX.

Could Some one tell me the addresses of the output window in LINUX,where we view the output of any C-Program.

[Salem]

> but how can we print a statement without using a printf in LINUX.
Well given say
char *p = "this is a message";

You can have puts(p);

or while ( *p ) putchar(*p++);

or write(1,p,strlen(p));

> Could Some one tell me the addresses of the output window in LINUX
There's no such thing. The whole of Linux is based on file descriptors, which could be anything from
- a real terminal
- a pseudo terminal
- a file
- another program.

If you're thinking of DOS, where you could cause things to appear on screen simply by writing some data to say b800:0000, then you're out of luck. There is no equivalent of that in Linux, or any other modern OS for that matter.

[Ancient Dragon]

In *nix you can use curses library which allows you to put characters on the screen in random locations. I also did it over 10 years ago using termio but I don't remember how I did it any more.

[narendharg]

I would thank you for replying to my query ,Could you please give the source code for system call function write().

[Salem]

I would imagine it's somewhere in the source code nearby where you found the source code for printf()

Where exactly is this question leading?

[narendharg]

I want to know how the values are printed on the output window i.e the code for write() or printf().

[Ancient Dragon]

What difference does it make how exactly it is done? The C standards do not dictate how its done so each compiler might do it differently. The characters are ultimately sent to the os and let the os display then on whatever terminal(s) happens to be attached to the computer.

If you really think you can read and understand the source code for write then you can get gcc version from www.gnu.org where they will give you free all the source code for their compiler. But be prepared for heavy-duty reading which very vew if anyone will help you.

[hneel]

Thanks for the code. I was googl'ing for a solution and this was just what I needed.

[jephthah]

you want the source code for the standard C library? ok, here it is: http://ftp.gnu.org/gnu/glibc/glibc-2.7.tar.gz

now please do feel free to go and knock yourself out. and if you can manage a specific, coherent, targeted question, I'm sure someone will try to help you.

but please don't feel free to repost entire source code files saying, "hay guys, how's all this stuff work?"

.