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digitalmars.D - Initialization of a local static variable with a member

reply Luke <kazade gmail.com> writes:
Hi all,

I've just started learning D (I've been programming C++ for 7 years). While I
was converting some old C++ code to D I've stumbled across this problem:

	float GetFPS(uint elapsedFrames = 1) {
		static LARGE_INTEGER s_lastTime = m_startTime; //< this line

This gives "ERROR: non-constant expression this.m_startTime". Is there any way
to avoid this error?
Nov 11 2007
parent reply "Janice Caron" <caron800 googlemail.com> writes:
On 11/11/07, Luke <kazade gmail.com> wrote:

 Hi all,

 I've just started learning D (I've been programming C++ for 7 years). While I
was converting some old C++ code to D I've stumbled across this problem:

         float GetFPS(uint elapsedFrames = 1) {
                 static LARGE_INTEGER s_lastTime = m_startTime; //< this line

 This gives "ERROR: non-constant expression this.m_startTime". Is there any way
to avoid this error?


Actually, what you're trying to do seems strange. m_startTime is a
member variable. GetFPS is a member function. So, what are you doing
using a "local static" (i.e. GLOBAL) variable at all? For a start,
it's not thread-safe.

In this particular example, I'd be inclined to make lastTime a private
class member variable. As in:

private LARGE_INTEGER lastTime;
float GetFPS(uint elapsedFrames = 1) {
    lastTime = startTime;
}
Nov 11 2007
parent BCS <ao pathlink.com> writes:
Reply to Janice,


 On 11/11/07, Luke <kazade gmail.com> wrote:
 

 Hi all,
 
 I've just started learning D (I've been programming C++ for 7 years).
 While I was converting some old C++ code to D I've stumbled across
 this problem:
 
 float GetFPS(uint elapsedFrames = 1) {
 static LARGE_INTEGER s_lastTime = m_startTime; //< this line
 This gives "ERROR: non-constant expression this.m_startTime". Is
 there any way to avoid this error?
 


 Actually, what you're trying to do seems strange. m_startTime is a
 member variable. GetFPS is a member function. So, what are you doing
 using a "local static" (i.e. GLOBAL) variable at all? For a start,
 it's not thread-safe.
 
 In this particular example, I'd be inclined to make lastTime a private
 class member variable. As in:
 
 private LARGE_INTEGER lastTime;
 float GetFPS(uint elapsedFrames = 1) {
 lastTime = startTime;
 }



assuming that adding it to the class adds to much memory and that you are 
assuming that only one "frame generation engine" will be running

float GetFPS(uint elapsedFrames = 1) {
startic LARGE_INTEGER lastTime = BeforeEverything;
lastTime = startTime;
}

OTOH I think Janice has a point.
Nov 11 2007