What is wrong with the "for" loop?

[Peter Olcott]

Everything in this program produces the correct results except the part
dealing with the RealList. The "for" loop does not output the values that
were input to the ALL[3].RealList. What is the correct syntax to for this?
Thanks

#include <stdio.h>
#include <string>
#include <vector>

union AllType {
int Int;
double Real;
std::string* Text;
std::vector<double>* RealList;
};

void main()
{
std::vector<AllType> ALL;
ALL.reserve(10);
printf("sizeof(ALL)--->%d\n", sizeof(ALL));
printf("sizeof(AllType)--->%d\n", sizeof(AllType));
ALL[0].Int = 31415926;
ALL[1].Real = 3.1415926;
ALL[2].Text = new std::string("Hell Oh Whirled");
ALL[3].RealList = new std::vector<double>;
ALL[3].RealList->reserve(3);
ALL[3].RealList->push_back(123.0);
ALL[3].RealList->push_back(456.0);
ALL[3].RealList->push_back(789.0);
printf("%d\n", ALL[0].Int);
printf("%f\n", ALL[1].Real);
printf("%s\n", ALL[2].Text->c_str());
for (unsigned int N = 0; N < ALL[3].RealList->size(); N++)
printf("%d) %f\n", N, ALL[3].RealList[N]);
}

[Peter van Merkerk]

"Peter Olcott" <ol****@worldnet.att.net> wrote in message
news:IR*********************@bgtnsc04-news.ops.worldnet.att.net...

Everything in this program produces the correct results except the part dealing with the RealList. The "for" loop does not output the values that were input to the ALL[3].RealList. What is the correct syntax to for this? Thanks

#include <stdio.h>
#include <string>
#include <vector>

union AllType {
int Int;
double Real;
std::string* Text;
std::vector<double>* RealList;
};

void main()
{
std::vector<AllType> ALL;
ALL.reserve(10);
printf("sizeof(ALL)--->%d\n", sizeof(ALL));
printf("sizeof(AllType)--->%d\n", sizeof(AllType));
ALL[0].Int = 31415926;
ALL[1].Real = 3.1415926;
ALL[2].Text = new std::string("Hell Oh Whirled");
ALL[3].RealList = new std::vector<double>;
ALL[3].RealList->reserve(3);
ALL[3].RealList->push_back(123.0);
ALL[3].RealList->push_back(456.0);
ALL[3].RealList->push_back(789.0);
printf("%d\n", ALL[0].Int);
printf("%f\n", ALL[1].Real);
printf("%s\n", ALL[2].Text->c_str());
for (unsigned int N = 0; N < ALL[3].RealList->size(); N++)
printf("%d) %f\n", N, ALL[3].RealList[N]);
}

The problem is that ALL[3].RealList is a pointer to a vector, rather
than the vector itself. Consequently the [] operator is performed on the
pointer rather than the vector. If you replace the for loop with this it
should work:

const std::vector<double>& v = *(ALL[3].RealList);
for (unsigned int N = 0; N < v.size(); N++)
{
printf("%d) %f\n", N, v[N]);
}

--
Peter van Merkerk
peter.van.merkerk(at)dse.nl

[André Pönitz]

Peter Olcott <ol****@worldnet.att.net> wrote:

void main()
int main()
{
std::vector<AllType> ALL;
ALL.reserve(10);
You want 'resize' here, not 'reserve' if you want room for 10 items
printf("sizeof(ALL)--->%d\n", sizeof(ALL));
[This is the size of the vector's private data, completely unrelated to
the number of items stored there]
ALL[1].Real = 3.1415926;
ALL[2].Text = new std::string("Hell Oh Whirled");
ALL[3].RealList = new std::vector<double>;
ALL[3].RealList->reserve(3);

Same here.

Andre'

--
Those who desire to give up Freedom in order to gain Security, will not have,
nor do they deserve, either one. (T. Jefferson or B. Franklin or both...)

[Andrew Koenig]

Peter> void main()
Peter> {
Peter> std::vector<AllType> ALL;
Peter> ALL.reserve(10);
Peter> printf("sizeof(ALL)--->%d\n", sizeof(ALL));
Peter> printf("sizeof(AllType)--->%d\n", sizeof(AllType));
Peter> ALL[0].Int = 31415926;
Peter> ALL[1].Real = 3.1415926;
Peter> ALL[2].Text = new std::string("Hell Oh Whirled");
Peter> ALL[3].RealList = new std::vector<double>;

These last four statements yield undefined behavior because ALL does
not have any elements, as you would see if you had executed

printf("ALL.size()--->%d\n", ALL.size()");

If you want to cause ALL to have 10 elements, you should execute

ALL.resize(10);

instead of calling reserve.
--
Andrew Koenig, ar*@acm.org