Vector used inside class definition appears to become static

[Barnaby Dawson]

Here is my code (abstracted from the original problem):

 #include <c:\djgpp\include\stdio.h> 
#include <c:\djgpp\include\stdlib.h>
#include <c:\djgpp\include\string.h>
#include <vector>
using namespace std;
 
class PhrasePool{
public:
vector<int> num;
PhrasePool(){
num[0]=1;
}
};
 
int main(){
PhrasePool TempPool,TempPool2;
for(int x=1;x<10;x++){
TempPool.num[x]=x;
}
for(int x=1;x<10;x++){
TempPool2.num[x]=10;
}
for(int x=0;x<10;x++){
printf("%d",TempPool.num[x]);
}
return 0;
}
 

I find when I run this program that I get the following output:
1101010101010101010

When I expect to get:
1123456789

Essentially I expect to have an individual copy of a vector of integers called num in each of TempPool and TempPool2. However it appears that I have just one shared vector of integers much as if I had declared the vector static.

Any clues as to why this is happening and/or how to fix the code so that it behaves as expected?

Thanks in advance to anyone kind enough to help.

[Barnaby Dawson]

A friend of mine has got back to me on this problem so I thought I'd post his answer here for the benefit of readers of this forum (and so others don't spend time telling me what I already know).

He says that num[x]=x is incorrect because the size of num is not known to be greater than x (indeed is not in this example). So instead I should use num.push_back(x) or resize the vectors ahead of time. I changed the code to use push_back(x) and it worked:

#include <c:\djgpp\include\stdio.h>
#include <c:\djgpp\include\stdlib.h>
#include <c:\djgpp\include\string.h>
#include <vector>
using namespace std;

int grabInt();
int phraseGrabInt(char input[],int pos);

FILE *filey;

class PhrasePool{
public:
vector<int> num;
PhrasePool(){
num.push_back(1);
}
};

int main(){
PhrasePool TempPool,TempPool2;
for(int x=1;x<10;x++){
TempPool.num.push_back(x);
}
for(int x=1;x<10;x++){
TempPool2.num.push_back(10);
}
for(int x=0;x<10;x++){
printf("%d",TempPool.num[x]);
}
return 0;
}

Presumably until the vectors had anything in them the [] operator gave the same locations in memory for both instances of the class (when looking beyond the actual end of the vector). There happened not to be anything using that location in memory so I got away with using it. When I wrote name.num[x] it accessed the same piece of memory whichever object it was within. Thats why it appeared to be static. The problems went away when I accessed the vectors in a valid way.