C++Talk.NET

Andreas Krueger · Guest

Hi!

I am fed up with
vector<int> iv;
iv.push_back(42); iv.push_back(9); iv.push_back(11); ...

and would rather use a function "fillVector":
vector<int> iv = fillVector(42,9,11);

like in Mathematica(tm): someList={42,9,11};
or even some2dimList={{42},{9,11}};

But there are some difficulties with it.
Perhaps you have good ideas how to solve it?
The sample code is below.
If you don't like templates, just leave out template<class T>
and replace every single "T" by "int"

a) In Visual C++ 6 the sample code works WITHOUT an ending 0:
25 vector<int> intvec=fillVector(800,500,200,300,400);
but in gcc 2.95.2 the last parameter HAS TO BE 0:
25 vector<int> intvec=fillVector(800,500,200,300,400,0);
otherwise the for(; Wink

breaks much later.

Moreover, even in Visual C++ 6, the problem occurs with
un-0-terminated lists when I use the vector result as
a parameter for some other function.
(see line 33) - so probably it's just by chance that it
works if I use an intermediate storage vector as in line 25

So: Is there any other way to notice the end (or length)
of a va_list ??? so that the list of parameters doesn't
need to be 0-terminated?

b) It works with "int" but not with "string"
because there doesn't seem to be a "0" in string - or is there?
compiler reports problem in line 15 because of (p==0)
even ( p == (T) 0 ) or a ( p == T(0) ) doesn't help.

any ideas concerning the "0" in string?

c) Any ideas for 2(3)dimensional arrays?
vector<vector intMatrix=fillVector((800,500),(200,300),(400,12));

Please answer not only to the list but also to my email...

Many thanks in advance!
Andreas

sample code:

1 #include <vector>
2 #include <algorithm>
3 #include <iostream>
4 using namespace std;
5 #pragma warning(disable:4786)
6
7 #include <cstdarg>
8 template<class T> vector<T> fillVector(T noZeroes ...){
9 vector<T> theVector;
10 theVector.push_back(noZeroes);
11 va_list ap;
12 va_start(ap, noZeroes);
13 for (; Wink

{
14 T p = va_arg(ap, T);
15 if (p==0 ) break;
16 theVector.push_back(p);
17 }
18 va_end(ap);
19 return theVector;
20 } // idea from chapter 7.6 of Stroustrup, 3rd Edition
21
22 void print_tab(int i) { cout< 23 void someFunction(vector for_each(v.begin(),v.end(),print_tab);
};
24
25 int main (){
26 vector<int> intvec=fillVector(800,500,200,300,400,0);
27 for_each(intvec.begin(),intvec.end(),print_tab);
28 cout<<"n";
29
30 // vector =fillVector<string > ("Andreas","Test","Schubbidu","");
31 // for_each(stringvec.begin(),stringvec.end(),print_tab);
32
33 someFunction(fillVector(800,500,200,300,400));
34 return 0;
35 }

Rob Williscroft · Guest

Andreas Krueger wrote in news:59499c44.0310180457.3d188c39
@posting.google.com:

Pete Becker · Guest

Rob Williscroft wrote:

Andreas Krueger · Guest

Hi!
I herewith suggest/demand a better variableLengthType "..."
for the next version of C++.

Thanks to M.Lehn, B.v.Ingen-Schenau and J.Sebastian for all
the suggestions for variable length parameter-functions
vector<T> foo(T data ...).
Some problems remain, though.

I summarize 4 possible solutions
(none of which are really elegant
cause there's NO way of knowing va-length):
a) specialized vector-/matrix-type with overloaded comma-operator
DoubleDenseVector b(3);
b = 1, 2, 3; ([url]http://sourceforge.net/projects/flens/)[/url])
b) first argument (or template argument)
contains length of data
c) using a C-style array as an intermediate container, e.g.:
int tmparr[] = { 42, 9, 11 };
vector<int> iv(tmparr, tmparr + sizeof tmparr / sizeof *tmparr);
d) a sentinel brackets the data.

I like solution (d) but there are still problems with VA_ARG
and STRING (access violation crash) 'cause "va_arg" stems from
C (not C++) as I was told.

So herewith I suggest a better variableLengthType "..."
for the next version of C++.

remaining problems with va_arg:

1)
One seems to need a template specialisation for each C++ type
like string. See code below at // (*)
Here the (const) string data has to be read-in by va_arg as char*
and then (implicitly) converted to string:
parameter = va_arg(ap, char*); // (*)

unfortunately a more compact version like
if (typeid(T)==typeid(string)) parameter = va_arg(ap, char*);
else parameter = va_arg(ap, T);
doesn't compile as soon as one uses fillVector<int>

1a) Why? Other ideas?

1b) Is complete specialisation the only way of solving the string problem?

2)
Why does one need a int- and string-specialisation for
template<class T> void print_tab(T i){ cout< if one wants to use
template for_each(v.begin(),v.end(),print_tab<T>); };
??

thanks a lot.
Andreas

#pragma warning(disable:4786)
#include <vector>
#include <algorithm>
#include <iostream>
#include <string>
using namespace std;
#include <cstdarg>

template<class T>
vector<T> fillVector(T sentinelDataSentinel ...){
T parameter, sentinel=sentinelDataSentinel;
vector<T> theVector;
va_list ap; va_start(ap, sentinelDataSentinel);
for (; Wink

{
parameter = va_arg(ap, T);
if ( parameter == sentinel ) break;
theVector.push_back(parameter);
}
va_end(ap);
return theVector;
};

template<>
vector<string> fillVector<string>(string sentinelDataSentinel ...){
string parameter, sentinel=sentinelDataSentinel;
vector<string> theVector;
va_list ap; va_start(ap, sentinelDataSentinel);
for (; Wink

{
parameter = va_arg(ap, char*); // (*)
if ( parameter == sentinel ) break;
theVector.push_back(parameter);
}
va_end(ap);
return theVector;
};

template<class T> void print_tab(T i){ cout< template<> void print_tab<string>(string i){ cout< template<> void print_tab<int> (int i) { cout<
template for_each(v.begin(),v.end(),print_tab<T>);
};

int main (){
vector<int> intvec=fillVector<int>(0,800,500,200,300,400,0);
coutVector<int>(intvec);
cout<<"n";
vector =fillVector<string>("stop","Andreas","Test","Schubbidu","stop");
coutVector<string>(stringvec);
return 0;
}

(Andreas Krueger) wrote in message news:<59499c44.0310180458.655b67da (AT) posting (DOT) google.com>...

Andreas Müller · Guest

Andreas Krueger wrote:

Andreas Krueger · Guest

red floyd · Guest

Andreas Krueger wrote:

red floyd · Guest

red floyd wrote:

Martijn Lievaart · Guest

On Mon, 20 Oct 2003 12:32:53 -0700, Andreas Krueger wrote:

Jerry Coffin · Guest

In article <59499c44.0310180457.3d188c39 (AT) posting (DOT) google.com>,
[email]usenet (AT) AndreasKrueger (DOT) de[/email] says...

Andreas Krueger · Guest

thought it might be necessary to mention this,
.... just for the protocol.

;-) Andreas