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Full Discussion: to convert int to hex
Top Forums Programming to convert int to hex Post 302152328 by DreamWarrior on Wednesday 19th of December 2007 03:35:19 PM
Old 12-19-2007
Quote:
Originally Posted by WebKruncher
#include <string>
#include <sstream>
using namespace std;

//This spends some extra cycles, offers simplicity, elegance and safety.
string IntToHexString(int i)
{
stringstream ss;
ss<<"0x"<<hex<<i;
string retval; retval=ss.str().c_str();
return retval;
}


//usage
cout<<"Hex for 32 is "<<IntToHexString(32)<<endl;
// as always handle your seh exceptions with a try / catch.
Correct me if I am wrong, but it also either 1) leaks memory, 2) reads a wild pointer, or 3) is thread unsafe:

Logically:

The .c_str call must return a "string".

Given:

A string is a pointer to a "NULL terminated string."

A "NULL terminated string" is a sequence of characters terminated by a '\0' character; we shall call this a "buffer".

A buffer resides somewhere in memory.

Therefore:

The .c_str call must return a pointer a buffer containing its contents.

In order not to leak, the above buffer must be freed at some point. To be freed the buffer must still referenced. Since the caller of IntToHexString does not take a reference then to not leak, either a) someone else must free it or b) someone else has a reference to it.

If (a) then the "somewhere" else may be the destructor of stringstream class. I presume this destructor is called when the stack for your function is cleaned up. This means that the string returned by IntToHexString becomes "wild" as soon as it returns.

If (b) then the buffer can be overwritten at some point by the class still holding a reference to it and therefore can not be thread safe.

If neither a nor b occurs then the code leaks. The only way this is untrue is if the compiler takes care of destroying the string returned by IntToHexString.
 

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LEARN ABOUT OPENSOLARIS

no-involuntary-power-cycles

no-involuntary-power-cycles(9P) 			   Kernel Properties for Drivers			   no-involuntary-power-cycles(9P)

NAME

       no-involuntary-power-cycles - device property to prevent involuntary power cycles

DESCRIPTION

       A  device  that might be damaged by power cycles should export the boolean (zero length) property no-involuntary-power-cycles to notify the
       system that all power cycles for the device must be under the control of the device driver.

       The presence of this property prevents power from being removed from a device or any ancestor of the device  while  the	device	driver	is
       detached, unless the device was voluntarily powered off as a result of the device driver calling pm_lower_power(9F).

       The  presence  of  no-involuntary-power-cycles  also forces attachment of the device driver during a CPR suspend operation and prevents the
       suspend from taking place, unless the device driver returns DDI_SUCCESS when its detach(9E) entry point is called with DDI_SUSPEND.

       The presence of no-involuntary-power-cycles does not prevent the system from being powered off due to a halt(1M) or uadmin(1M)  invocation,
       except for CPR suspend.

       This  property  can be exported by a device that is not power manageable, in which case power is not removed from the device or from any of
       its ancestors, even when the driver for the device and the drivers for its ancestors are detached.

EXAMPLES

       Example 1 Use of Property in Driver's Configuration File

       The following is an example of a no-involuntary-power-cycles entry in a driver's .conf file:

	 no-involuntary-power-cycles=1;
	      ...

       Example 2 Use of Property in attach() Function

       The following is an example of how the preceding .conf file entry would be implemented in the attach(9E) function of a driver:

	 xxattach(dev_info_t *dip, ddi_attach_cmd_t cmd)
	   {
	    ...
		if (ddi_prop_create(DDI_DEV_T_NONE, dip, DDI_PROP_CANSLEEP,
		    "no-involuntary-power-cycles", NULL, 0) != DDI_PROP_SUCCESS)
		     goto failed;
	    ...
	    }

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface stability	     |Committed 		   |
       +-----------------------------+-----------------------------+

SEE ALSO

       attributes(5), pm(7D), attach(9E), detach(9E), ddi_prop_create(9F)

       Writing Device Drivers

SunOS 5.11							    22 Mar 2001 				   no-involuntary-power-cycles(9P)
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