floating point problem in C

[rajarora]

Following is the small code snippet which is giving strange results .

--------------------------------------------------------------------------------

#include <stdio.h>
#include <string.h>
 
int main()
{
   float f= 1256.35;
   char ch[4];
 
   printf("\n1. f  : %f",f);
   memset(ch,'\0',strlen(ch) );
   printf("\n2. f  : %f",f);
   return 0;
}
 

--------------------------------------------------------------------------------

Expected output is
1. f : 1256.349976
2. f : 1256.349976

But I am getting the output
1. f : 1256.349976
2. f : 0.000000

Can you help in getting the solution of this problem. I have tried it on sun-solaris as well as on VC++ platform and I am getting the same results.

[rajarora]

Ok Friends,
I got the solution of this problem. Actually in place of strlen() in memset() call ;
we need to use the sizeof().
So the modified code which is now working correctly

#include <stdio.h>
#include <string.h>
int main()
{
   float f= 1256.35;
   char ch[4];
 
   printf("\n1. f  : %f",f);
   memset(ch,'\0',sizeof(ch) );
   printf("\n2. f  : %f",f);
   return 0;
}
 
 

Following is the small code snippet which is giving strange results .

--------------------------------------------------------------------------------

#include <stdio.h>
#include <string.h>
 
int main()
{
   float f= 1256.35;
   char ch[4];
 
   printf("\n1. f  : %f",f);
   memset(ch,'\0',strlen(ch) );
   printf("\n2. f  : %f",f);
   return 0;
}
 

--------------------------------------------------------------------------------

Expected output is
1. f : 1256.349976
2. f : 1256.349976

But I am getting the output
1. f : 1256.349976
2. f : 0.000000

Can you help in getting the solution of this problem. I have tried it on sun-solaris as well as on VC++ platform and I am getting the same results.

[ashitpro]

Ok Friends,
I got the solution of this problem. Actually in place of strlen() in memset() call ;
we need to use the sizeof().
So the modified code which is now working correctly

#include <stdio.h>
#include <string.h>
int main()
{
   float f= 1256.35;
   char ch[4];
 
   printf("\n1. f  : %f",f);
   memset(ch,'\0',sizeof(ch) );
   printf("\n2. f  : %f",f);
   return 0;
}
 
 

strlen looks for '\0', that we don't have in 'ch',
So strlen will return unspecified value(length till it gets the '\0').
In my case it used to return 17 instead of 4.
And very next statement(memset) makes next 17 bytes zeroed and probably overwriting the float value.

[rajarora]

Thanks yar,

that is the thing i m looking for.

Regards
Raj Kr Arora

strlen looks for '\0', that we don't have in 'ch',
So strlen will return unspecified value(length till it gets the '\0').
In my case it used to return 17 instead of 4.
And very next statement(memset) makes next 17 bytes zeroed and probably overwriting the float value.