Interesting implementation: atol, atof etc Post: 302184048

Sponsored Content

Top Forums Programming Interesting implementation: atol, atof etc Post 302184048 by karthikb23 on Thursday 10th of April 2008 11:23:21 AM

04-10-2008

Registered User

Interesting implementation: atol, atof etc

Hi,
Check the following code:

#include <stdio.h>

int main()
{
char *s="123.33";

double d=0.0;

d = (double)atof(s);

printf("s is %2$s, d is %1$f\n", d, s);

d = (double)strtod(s, NULL);

printf("s is %3$s, d is %1$.*2$f\n", d, 2, s);

return 0;
}

Output:
s is 123.33, d is 133592.000000
s is 123.33, d is 133592.00

Quite Obvious: I have not included <stdlib.h>
But my code still compiles, because 'libc' is anyways referenced (eg: printf).

=> What are these values returned? This implies there is a 'default' atof which has resolved the symbol reference.

Something interesting now, is i can define atof as a local function: a global symbol and use it as i like.

Now my Question/Problem

But what i was very surprised to see is:
$: nm -A /usr/lib/libc.so.1 | grep atof
/usr/lib/libc.so.1: [3266] | 207888| 12|FUNC |GLOB |0 |9
|atof

'atof' is a symbol with Global visibility in libc.

My questions:
1. Standard C functions should be defined as WEAK symbols, so that a user can override them, like in the above case.
2. However, the resolution in above case has happened due to concept of "interposition" in shared libraries.

Am I correct in concluding this?
Please advice.

karthikb23

View Public Profile for karthikb23

Find all posts by karthikb23

4 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Interesting question :-D

first off, i LOVE unix to death, but i really only like the text/console side of it. im not big into the XFree86/Xwindows side of things.. so with that known... im in search of really old *nix's.. like way outdated, floppy OS's from way back in the day. im kinda in search of the pure'r UNIX's....

2. Shell Programming and Scripting

Here is an interesting idea...

Does anyone know how to test if an ethernet interface is alive, or accepting connections? Here is the scenario - I have rsc and sc console interfaces on some Suns. There are some sporadic vulnerability scans that send them out to lunch when they run the scans. I have to login to the host and reset...

3. Shell Programming and Scripting

Interesting problem

Hello, So I'm utilizing the bash brace expansion feature to checkout multiple folders from cvs with ease, while excluding certain subfolders within. So I do a command like this: cvs co trunk/{mod_a,mod_b,mod_c} \!trunk/{mod_a,mod_b,mod_c}/web to checkout modules trunk/mod_a , trunk/mod_b ,...

4. Programming

atof problem

Hi I have a small code snippet. printf("sTaTuS |%s| , |%s| => %f , %f \n",before,after,strtod(before,0),strtod(after,0)); If the variables before and after has values 1000.2234 and 1000.0234 then i get the following output. sTaTuS |1000.2234| , |1000.0234| => 0.000000 , -0.000000 ...

LEARN ABOUT OSX

atof

ATOF(3) 						   BSD Library Functions Manual 						   ATOF(3)

NAME

     atof, atof_l -- convert ASCII string to double

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdlib.h>

     double
     atof(const char *str);

     #include <xlocale.h>

     double
     atof_l(const char *str, locale_t loc);

DESCRIPTION

     The atof() function converts the initial portion of the string pointed to by str to double representation.

     It is equivalent to:

	   strtod(str, (char **)NULL);

     The decimal point character is defined in the program's locale (category LC_NUMERIC).

     While the atof() function uses the current locale, the atof_l() function may be passed a locale directly. See xlocale(3) for more informa-
     tion.

IMPLEMENTATION NOTES

     The atof() and atof_l() functions are thread-safe and async-cancel-safe.

     The atof() and atof_l() functions have been deprecated by strtod() and strtod_l() and should not be used in new code.

ERRORS

     The function atof() need not affect the value of errno on an error.

SEE ALSO

     atoi(3), atol(3), strtod(3), strtol(3), strtoul(3), xlocale(3)

STANDARDS

     The atof() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1''), ISO/IEC 9899:1990 (``ISO C90''), and ISO/IEC 9899:1999 (``ISO C99'').

BSD
								   June 4, 1993 							       BSD