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sprintf Issue

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Join Date: Sep 2008

Posts: 62

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AutoC

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sprintf Issue

Feb 7th, 2009

I have a code snippet that strangely works one way on a fedora 6 machine and another way on a fedora 8 machine.

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void Form1::SendToApp()
{
  vector<int> isciistream;
  vector<int> fontstream;
  cout<<"Entering Form1::SendToApp()"<<endl;
  isciistream=wwnd->OnOK();
  isciistream.push_back(32);
  char str[255]="";
  cout<<"Size of IsciiStream:"<<isciistream.size()<<endl;
  for (int i=0;i<(int)isciistream.size();i++)
  {
    sprintf(str,"%s%c",str,isciistream[i]);
    cout << "isciistream[i] :" << isciistream[i]<< " str:"<<str[i]<<endl;
  }
 
 QString temp=str;
const char *foo = temp.ascii();
cout<<"foo:"<<(int)foo[0]<<","<<(int)foo[1]<<","<<(int)foo[2]<<endl;
}
void Form1::SendToApp()
{
  vector<int> isciistream;
  vector<int> fontstream;
  cout<<"Entering Form1::SendToApp()"<<endl;
  isciistream=wwnd->OnOK();
  isciistream.push_back(32);
  char str[255]="";
  cout<<"Size of IsciiStream:"<<isciistream.size()<<endl;
  for (int i=0;i<(int)isciistream.size();i++)
  {
    sprintf(str,"%s%c",str,isciistream[i]);
    cout << "isciistream[i] :" << isciistream[i]<< " str:"<<str[i]<<endl;
  }

 QString temp=str;
const char *foo = temp.ascii();
cout<<"foo:"<<(int)foo[0]<<","<<(int)foo[1]<<","<<(int)foo[2]<<endl;
}

for eg. if isciistream.size=3
isciistream[0]=204
isciistream[1]=32
isciistream[2]=32

on a fedora 6 machine the output i get is
foo: -52,32,32
which is correct.
in a fedora 8 machine i get
foo:32,0,43
I'm not sure why...

any help is appreciated

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Join Date: Dec 2005

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Salem

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Void main'ers are DOOMed

Re: sprintf Issue

Feb 7th, 2009

> sprintf(str,"%s%c",str,isciistream[i]);
1. Almost all C library functions have undefined behaviour when the source and destination overlap. You're reading from the string you're printing into.

2. QString temp=str;
> const char *foo = temp.ascii();
If you print out the bytes of str before this, are they OK?
Perhaps QString defaults to a wide char on F8