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Problem with STL sort.

Hi all,
I am using the STL sort to a vector whose every element is an instance
type "struct data" as defined below:

However, when I am trying to compile the code, I am getting the
following error:

/usr/include/c++/3.4.3/bits/stl_algo.h:90: error: passing 'const
SerialNumbers::data' as 'this' argument of 'bool
SerialNumbers::data::operator<(const SerialNumbers::data&)' discards
Can anybody please explain to me what that error means?

I am using the g++ to compile my code.
The code follows:

#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <algorithm>
#include <sstream>

using namespace std;

class Test {

struct data
string str;

bool operator < (const data& d2)

return false;



vector <stringsortSerials(vector <stringinp)
for(int i=0; i < inp.size(); ++i)
data d;
d.str = inp.at(i);


for(int i=0; i < table.size(); ++i)

return ret;

} // the method ends here.

Oct 20 '07 #1
2 1828
On 2007-10-20 15:17:12 -0400, alice <al***********@yahoo.comsaid:
/usr/include/c++/3.4.3/bits/stl_algo.h:90: error: passing 'const
SerialNumbers::data' as 'this' argument of 'bool
SerialNumbers::data::operator<(const SerialNumbers::data&)' discards
Can anybody please explain to me what that error means?
It means that operator< takes one of its arguments as a non-const
reference. Since the named argument is const&, it must be the other one.
bool operator < (const data& d2)
bool operator <(const data& d2) const;

Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference

Oct 20 '07 #2
alice wrote:
discards qualifiers
You have to learn what g++ means with its error messages.

"Discards qualifiers" means in at least 90% of cases that a non-const
(usually a function) is being used where a const is expected. In other
words, the function must be const for that specific situation.
Oct 20 '07 #3

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