Re: integer in ostringstream
cerr wrote:
On May 26, 10:43 am, Bart van Ingen Schenau <b...@ingen.ddns.info>
wrote:
cerr wrote:
Hi Chris,
Thanks for your reply!
getPriorityNeed() looks is just a simple method to read an integer
in a thread safe manner:
int GPSData::getPriorityNeed()
{
int value;
novax_thread_lock(&priorityNeed_mtx);
//calculate priority with data from config file and deviation
from
INIT!
value = GPSData::priorityNeed;
novax_thread_unlock(&priorityNeed_mtx);
return value;
}
GPSData::priorityNeed gets set by
void GPSData::setPriorityNeed(int value)
{
novax_thread_lock(&priorityNeed_mtx);
GPSData::priorityNeed = value;
novax_thread_unlock(&priorityNeed_mtx);
}
which gets called regularly from a thread.
The object GPSData::priorityNeed is declared as a private integer.
So why would getPriorityNeed return a correct value most of the
times but every now and then it seems to mess it up... Not very
often tho and as said, I can't really figure out any regularity...
:o
There are two possible causes for that wrong value to turn up:
1. An incorrect value gets passed to setPriorityNeed. This should be
caught with an assert in setPriorityNeed, after which you can trace
back in the debugger who is responsible for that wrong value.
Thats' what I thought as well first but then again, the value that
gets set there is from the type bool (in this case, can be integer in
other cases that's why i'm using int as the type to save the value)
How sure are you that those other cases (with non-boolean values) do net
get triggered just before you read the value?
2. You have a rogue pointer in your program that causes the value of
GPSData::priorityNeed to be overwritten. This is a very serious
problem that can only be located with a lot of hard effort and
critically looking at ALL of the code.
Nu-uh, I don't think so as the other values from the same pointer are
always correct.
But I am not talking about the situation that the pointer you use to
legitimately access the data is invalid.
I am talking about the case that *some other pointer* overwrites your
data.
for example, something like this:
int main()
{
char* p1 = new char[4];
delete p1;
int* p2 = new int; // SAME ADDRESS AS p1!
p2 = 42;
p1[1] = 'A'; // trashes p2 !
}
I believe it is as fenghuang earlier suggested "just"
a casting issue:
I can guarantee you that casting will not make your problem disappear.
The cast to unsigned int will cause the incorrect value to be
2147483648.
char * str = NULL;
char ch = '\0';
int i = 0;
unsigned int u = 0;
// in fact, the three variables have same content
With my addition, all four.
but
std::cout << str;
std::cout << ch;
std::cout << 0;
have different results
That is true, but it is beside the point.
std::cout << 0;
and
std::cout << 0u;
have identical results.
Thanks,
--
roN
Bart v Ingen Schenau
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