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Hi all,

I am getting conversion error when I try to read data into SSQLS structure and value of an integer field is null. I modified example stock table to have NULL values for num field and customX examples fail with the same error:

Conversion error: Tried to convert "NULL" to a "__int64
retrieved data size: 0, actual size: 4

How do you get around this problem.

Thanks.



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Ece Karli wrote:

Read the user manual. There is a whole section on nulls (3.8), and why
you have to treat them specially.

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I have already read that section but could not get Null template compile if the type in the sql_create macro is one of those. I have copied my modified version of custom1.cpp file below. I am getting this compile error:

d:\mysql++\include\coldata.h(300) : error C2666: 'mysqlpp::const_string:perator`[]'' : 2 overloads have similar conversions
d:\mysql++\include\const_string.h(137): could be 'mysqlpp::const_string::const_reference mysqlpp::const_string:perator [](mysqlpp::const_string::size_type) const'
or 'built-in C++ operator[(mysqlpp::cchar, int)'
while trying to match the argument list '(const mysqlpp::ColData_Tmpl<Str>, int)'
with
[
Str=mysqlpp::const_string
]
d:\Test\TestMySQL\TestMySQL.cpp(57) : see reference to function template instantiation 'mysqlpp::ColData_Tmpl<Str>:perator`mysqlpp::Nul l<Type,Behavior>'(void) const' being compiled
with
[
Str=mysqlpp::const_string,
Type=double,
Behavior=mysqlpp::NullisZero
]


How am I supposed to use the template in that macro? Here is the code, I am trying to define weight as nullable field:

typedef mysqlpp::Null<double, mysqlpp::NullisZero> MyNull;

sql_create_5(stock,
1, 5, // explained in the user manual
string, item,
mysqlpp::longlong, num,
MyNull, weight,
double, price,
mysqlpp:ate, sdate)

int
main(int argc, char *argv[])
{
// Wrap all MySQL++ interactions in one big try block, so any
// errors are handled gracefully.
try {
// Establish the connection to the database server.
mysqlpp::Connection con(mysqlpp::use_exceptions);
if (!connect_to_db(argc, argv, con)) {
return 1;
}
// Retrieve the entire contents of the stock table, and store
// the data in a vector of 'stock' SSQLS structures.
mysqlpp::Query query = con.query();
query << "select * from stock";
vector<stock> res;
query.storein(res);
// Display the result set
print_stock_header(res.size());
vector<stock>::iterator it;
for (it = res.begin(); it != res.end(); ++it) {
print_stock_row(it->item, it->num, it->weight, it->price,
it->sdate);
}
}
catch (const mysqlpp::BadQuery& er) {
// Handle any query errors
cerr << "Query error: " << er.what() << endl;
return -1;
}
catch (const mysqlpp::BadConversion& er) {
// Handle bad conversions; e.g. type mismatch populating 'stock'
cerr << "Conversion error: " << er.what() << endl <<
"\tretrieved data size: " << er.retrieved <<
", actual size: " << er.actual_size << endl;
return -1;
}
catch (const mysqlpp::Exception& er) {
// Catch-all for any other MySQL++ exceptions
cerr << "Error: " << er.what() << endl;
return -1;
}
return 0;
}


Warren Young <mysqlpp (AT) etr-usa (DOT) com> wrote:
Ece Karli wrote:

Read the user manual. There is a whole section on nulls (3.8), and why
you have to treat them specially.


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Thanks for the reply. However, I don't see myself writing a patch yet,
I'm just not that skilled with my C++ programming But I'm learning
and maybe, some day, I will be usefull
Does someone know where I can find some information, where I can learn
what is causing the problem and how I can avoid it? Maybe I can work
around it to avoid the problem.

Op do, 20-04-2006 te 06:22 -0600, schreef Warren Young:
If Linux doesn't have the solution, you have the wrong problem


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M.K. tenNapel wrote:
You misunderstand: the thread I pointed you to _contains_ a patch,
already written.

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I saw that just after I send my mail. Sorry for that
I'll see if I can get it to work. Thanks!

Op do, 20-04-2006 te 13:07 -0600, schreef Warren Young:
If Linux doesn't have the solution, you have the wrong problem


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