float_control

 

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The latest version of this topic can be found at float_control. Specifies floating-point behavior for a function.

Syntax

float_control( value,setting [push] | push | pop )  

Flags

value , setting [push]
Specifies floating-point behavior. value can be precise or except. For more information, see /fp (Specify Floating-Point Behavior). setting can either be on or off.

If value is precise, the settings for precise and except are being specified. except can only be set to on when precise is also set to on.

If the optional push token is added, the current setting for value is pushed on to the internal compiler stack.

push
Push the current float_control setting on to the internal compiler stack

pop
Removes thefloat_control setting from the top of the internal compiler stack and makes that the new float_control setting.

Remarks

You cannot turn float_control precise off when except is on. Similarly, precise cannot be turned off when fenv_access is on. To go from strict model to a fast model with the float_control pragma, use the following code:

#pragma float_control
(except, off)  
#pragma fenv_access
(off)  
#pragma float_control
(precise, off)  
// The following line is needed on Itanium processors  
#pragma fp_contract
(on)  

To go from fast model to a strict model with the float_control pragma, use the following code:

#pragma float_control
(precise, on)  
#pragma fenv_access
(on)  
#pragma float_control
(except, on)  
// The following line is needed on Itanium processors.  
#pragma fp_contract
(off)  

Other floating-point pragmas include:

• fenv_access

• fp_contract

Example

The following sample shows how to catch an overflow floating-point exception by using pragma float_control.

// pragma_directive_float_control.cpp  
// compile with: /EHa  
#include <stdio.h>  
#include <float.h>  
  
double func( ) {  
   return 1.1e75;  
}  
  
#pragma float_control (except,on)  
  
int main( ) {  
   float u[1];  
   unsigned int currentControl;  
   errno_t err;  
  
   err = _controlfp_s(&currentControl, ~_EM_OVERFLOW, _MCW_EM);  
   if (err != 0)  
      printf_s("_controlfp_s failed!\n");  
  
   try  {  
      u[0] = func();  
      printf_s ("Fail");     
      return(1);  
   }   
  
   catch (...)  {  
      printf_s ("Pass");  
      return(0);  
   }  
}  

Pass  

See Also

Pragma Directives and the __Pragma Keyword