passing as 'this' argument of discards qualifiers

[yyiu002]

Hi , I have a problem when compile following code:

for(int i=0;i<curConnections.size();++i)
    {
        if (curConnections.at(i).Descriptor()==connName)
        {
            curConnections.at(i).sendCmd(cmd);
            break;
        }
    }

for(int i=0;i<curConnections.size();++i)
    {
        if (curConnections.at(i).Descriptor()==connName)
        {
            curConnections.at(i).sendCmd(cmd);
            break;
        }
    }

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Compiler complains:
error: passing 'const ConnConnection' as 'this' argument of 'void ConnConnection::sendCmd(const QString&)' discards qualifiers

Then I use following it compiles OK.

curConnections[i].sendCmd(cmd);

curConnections[i].sendCmd(cmd);

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I am not quite get what's the difference of these 2 lines of code.