Go4Expert - confusion with format string

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- - confusion with format string (http://www.go4expert.com/showthread.php?t=8431)

shyam_oec

24Jan2008 00:12

confusion with format string

main()
{
float x=1.0;
int y=3;
printf("x=%d",x);
printf("\ny=%f",y);
}

output:
x=0
y=285737.000011(why this unexpected output?) :confused:

though x is floating type variable,when it is displayed in int farmat why it's output is x=0
on the other hand value of y is something annoying

Salem

24Jan2008 00:46

Re: confusion with format string

You used the wrong format for the printf commands.

Code:

$ gcc -W -Wall -ansi -pedantic -O2 foo.c

foo.c: In function `main':

foo.c:14: warning: int format, double arg (arg 2)

foo.c:15: warning: double format, different type arg (arg 2)

shabbir

24Jan2008 07:48

Re: confusion with format string

%d and %f are for integer and float respectively.

shyam_oec

24Jan2008 11:56

Re: confusion with format string

Quote:

Originally Posted by shabbir

%d and %f are for integer and float respectively.

it's fine that %d and %f are for integer and float,but can u tell why we get such an output....

Salem

24Jan2008 13:49

Re: confusion with format string

> but can u tell why we get such an output.
Because your code is broken.

Broken code produces whatever it feels like, regardless of what you might expect / like / desire / hope for.

Use a compiler which can check your printf / scanf format strings (like I posted), and don't run any code which has warnings in it.

asadullah.ansari

24Jan2008 14:20

Re: confusion with format string

When you will go definition of printf. A sample of it..

Code:

int printf( . . . )

{

     //Some code

   ...........

   ...............

  //va_arg : taking conversion symbol(%d, %f etc) and associated with values

 switch( TYPE)

 { 



  //Case INT_TYPE : Some code for Integer

  // Case FLOAT_TYPE : some code for Float 

  // Case CHAR_TYPE  : some code for char

    ......

   .....

  }

return ;

}

when conversion sybol(%d) and value is double then it's value will be junk. because printf function does not check for type casting. Just %d and its associated values. If it's matching then it will go correct switch case and correct value. Else wrong switch case will execute and value will be junk.

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