Re: Static variable in template function

From:

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <daniel.kruegler@googlemail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 6 Jun 2010 16:19:34 CST

Message-ID:

<fa73a8c5-fff8-45fc-9fae-6d4648c03501@w31g2000yqb.googlegroups.com>

On 6 Jun., 17:14, LiloLilo <danilobrambi...@tiscali.it> wrote:

Hi all,

the following function writes n bits data to file. Parameter named
'Data' contains the value to be written, 'Length' contains the number
of bits of 'Data' to write. This function uses a static buffer named
BitBuffer to store bits between calls. When BitBuffer is full it is
written to file.

void WriteBitsToFile(unsigned Data, unsigned Length, std::ofstream &
OutFile) {

        static unsigned BitBuffer = 0; static unsigned BitCounter =
0;

        for (unsigned i = Length; i --; ) {

                (BitBuffer <<= 1) |= ((Data >> i) & 0x1); BitCounter +
+;

                if (BitCounter == 32) { OutFile.write((char *) &
BitBuffer,
sizeof(BitBuffer)); BitCounter = 0; }
        }

        TotalBitCounter += Length;

}

The function works fine, but if I change 'Data' to a templated
variable, BitBuffer gets flushed to 0 at every call, so it does not
retains values between calls. Please note that calls are made always
with the same type for T2 (int) so if I am not wrong it would retain
the value but it doesn't. Why?

template <typename T2> void WriteBitsToFile(T2 Data, unsigned Length,
std::ofstream & OutFile) {

        static unsigned BitBuffer = 0; static unsigned BitCounter =
0;

        for (unsigned i = Length; i --; ) {

                (BitBuffer <<= 1) |= ((Data >> i) & 0x1); BitCounter +
+;

                if (BitCounter == 32) { OutFile.write((char *) &
BitBuffer,
sizeof(BitBuffer)); BitCounter = 0; }
        }

        TotalBitCounter += Length;

}

Thank you all for help.

Please show us a complete program that demonstrates
the problem directly. If your analysis would be
correct, it should probably be reproducible. E.g.
what is the outcome of the following program given
your compiler:

#include <iostream>

void foo() {
   static int a = 0;
   std::cout << a << ", ";
   a += 1;
}

template<class>
void foo() {
   static int a = 0;
   std::cout << a << ", ";
   a += 1;
}

int main() {
   for (int i = 0; i < 3; ++i) {
     foo();
   }
   std::cout << std::endl;
   for (int i = 0; i < 3; ++i) {
     foo<int>();
   }
}

An conforming implementation should output:

0, 1, 2,
0, 1, 2,

Which compiler (including version) are you using?

HTH & Greetings from Bremen,

Daniel Kr?gler

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