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Home » Community » Newbie corner » Pick Semantics: Passing a Vector to a method
| Pick Semantics: Passing a Vector to a method [message #40143] |
Thu, 20 June 2013 21:42  |
NeilMonday
Messages: 15
Registered: May 2013
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Promising Member |
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I am learning about pick semantics now. Lets assume I wanted to print a Vector of Strings two times. Am I right in assuming that this will not work:
void PrintNames(Vector<String> names)
{
for(int i=0; i<names.GetCount(); i++)
{
//print the name
}
}
int main()
{
Vector<String> myNames;
//add a few Strings to myNames here...
PrintNames(myNames);
//myNames is not valid anymore?
PrintNames(myNames);
}
Instead I will need to do this:
void PrintNames(Vector<String> names)
{
for(int i=0; i<names.GetCount(); i++)
{
//print the name
}
}
int main()
{
Vector<String> myNames;
//add a few Strings to myNames here...
Vector<String> tempNames;
tempNames <<= myNames;
PrintNames(tempNames);
tempNames <<= myNames;
PrintNames(tempNames);
}
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| Re: Pick Semantics: Passing a Vector to a method [message #40146 is a reply to message #40143] |
Fri, 21 June 2013 06:24  |
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Hi Neil,
Welcome to the forum 
| NeilMonday wrote on Thu, 20 June 2013 21:42 |
I am learning about pick semantics now. Lets assume I wanted to print a Vector of Strings two times. Am I right in assuming that this will not work:
void PrintNames(Vector<String> names)
{
for(int i=0; i<names.GetCount(); i++)
{
//print the name
}
}
int main()
{
Vector<String> myNames;
//add a few Strings to myNames here...
PrintNames(myNames);
//myNames is not valid anymore?
PrintNames(myNames);
}
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Yes, you understand that correctly. The first call would "pick" the contents of the original vector and the second call would show nothing or even thrown error.
| NeilMonday wrote on Thu, 20 June 2013 21:42 |
Instead I will need to do this:
void PrintNames(Vector<String> names)
{
for(int i=0; i<names.GetCount(); i++)
{
//print the name
}
}
int main()
{
Vector<String> myNames;
//add a few Strings to myNames here...
Vector<String> tempNames;
tempNames <<= myNames;
PrintNames(tempNames);
tempNames <<= myNames;
PrintNames(tempNames);
}
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This would work, but it has terrible overhead. It is not necessary to copy the vector at all, you can just to pass it to the PrintNames as a reference (in this case you can even use const reference):
// all you need to do is to add one little '&' ;-) the const is optional
void PrintNames(const Vector<String>& names)
{
for(int i=0; i<names.GetCount(); i++)
{
//print the name
}
}
int main()
{
Vector<String> myNames;
//add a few Strings to myNames here...
PrintNames(myNames);
PrintNames(myNames);
}
Since there is now no copying, there is no pick to worry about  In general, you should use references as often as possible, it is a great boost to performance, especially for large containers.
Best regards,
Honza
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