How to initialize a static member of a parametrized-template class

Question

I don't think my question is a duplicate of this one.

what I try to do:

template<const char* szFunctionName> class CReentranceLock { public: CReentranceLock(){} ~CReentranceLock(){} bool isLocked(){return s_bLock;} void setLocked(bool b) { const bool Result=(bool)InterlockedCompareExchange( (unsigned long *)&s_bLock, b, !b); } private: static bool s_bLock; }; template<const char* szFunctionName> bool CReentranceLock<const char*szFunctionName>::s_bLock=false; // error C2146: syntax error : missing ',' before identifier 'szFunctionName'

implying that all instances of CReentranceLock would have their own static, relying on the const char address of the function name passed as a parameter of the template.

and that could be used like this:

void CMyObject::InAnyFunction() { const char* szFunctionName = __FUNCTION__; CReentranceLock<szFunctionName> lock; // Edit: <- this doesn't work if(lock.isLocked()) return; lock.setLocked(true); /// business code lock.setLocked(false); }

well that's only the theory... and unfortunately this doesn't compile under visual 2010, at the line where I try to initialize the statics.

error C2146: syntax error : missing ',' before identifier 'szFunctionName'

what am I doing or thinking wrong ?

PS: and I am not dealing with the fact that reentrance is smelling like an awful design (in MFC), I know, I am lost in the middle of it ;-)

Edit: though the answer below is good, and the definition compiles... my use in CMyObject::InAnyFunction() with a const char * as a template-parameter available at compile time seems to be wrong. :-(

The member s_bLock itself does not exist unless you instance a CReentranceLock. the szFunctionName is only a placeholder name that does not exist (as the compiler warns you). Try const char Foo[] = {"Foo"}; bool CReentranceLock<Foo>::s_bLock=false; instead. (but you will set only the s_bLock of the Foo instance type of CReentranceLock). — PaperBirdMaster
– PaperBirdMaster, Commented Jun 22, 2012 at 9:14
@StephaneRolland: Are you suggesting that const char * is convertible to an int? — dirkgently
– dirkgently, Commented Jun 22, 2012 at 9:24
@dirkgently well, that's what I intimately think, though it may depends whether you are on a 32 or 64 bits system. on a 64 bits system, I think it's a 64 bits integer. — Stephane Rolland
– Stephane Rolland, Commented Jun 22, 2012 at 9:29

Griwes · Accepted Answer · 2012-06-22 09:15:34Z

bool CReentranceLock<const char*szFunctionName>::s_bLock=false;

This should be:

bool CReentranceLock<szFunctionName>::s_bLock=false;

Raj · Accepted Answer · 2012-06-22 09:21:58Z

0

Just change the line to

bool CReentranceLock<szFunctionName>::s_bLock=false;

edited Jun 22, 2012 at 9:21

answered Jun 22, 2012 at 9:16

Raj

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2 Comments

Griwes Over a year ago

Nope, you need to use template parameter (even if templated) there.

Raj Over a year ago

Sorry about that. A typo. Since the answer's already provided, i'll edit it

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