[SOLVED] QVector iterator seg fault using .begin/.end

[pheonixstorm]

Built an app (don't sue me apple!) very similar to the addressbook tutorial (used QVector not QMap) and having issues using a next and previous function. As far as I can tell when it gets to checking for it == .begin() and changin it = .end() the it crashes instead of going to the end of the vector.

mpledit.cpp

void MplEdit::previousCargo()
{
    if (it == MPLVec.begin())
        it = MPLVec.end();
 
    if (it == MPLVec.end()) {
        ui->fileEdit->clear();
        ui->categoryEdit->clear();
        ui->priceEdit->clear();
        ui->massEdit->clear();
        ui->volumeEdit->clear();
        ui->descEdit->clear();
    }
 
    ui->fileEdit->setText(it->getFile());
    ui->categoryEdit->setText(it->getCategory());
    ui->priceEdit->setText(it->getPrice());
    ui->massEdit->setText(it->getMass());
    ui->volumeEdit->setText(it->getVolume());
    ui->descEdit->setText(it->getDesc());
 
    it--;
}

void MplEdit::previousCargo()
{
    if (it == MPLVec.begin())
        it = MPLVec.end();

    if (it == MPLVec.end()) {
        ui->fileEdit->clear();
        ui->categoryEdit->clear();
        ui->priceEdit->clear();
        ui->massEdit->clear();
        ui->volumeEdit->clear();
        ui->descEdit->clear();
    }

    ui->fileEdit->setText(it->getFile());
    ui->categoryEdit->setText(it->getCategory());
    ui->priceEdit->setText(it->getPrice());
    ui->massEdit->setText(it->getMass());
    ui->volumeEdit->setText(it->getVolume());
    ui->descEdit->setText(it->getDesc());

    it--;
}

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mpledit.h

QVector<MPL> MPLVec;
    QVector<MPL>::iterator it;
    QVector<MPL>::const_iterator sav;

QVector<MPL> MPLVec;
    QVector<MPL>::iterator it;
    QVector<MPL>::const_iterator sav;

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When i mouseover MPLVec.begin() it tells me that begin is const_iterator QVector::begin const when I *think* it should be telling me iterator QVector::begin () instead. Don't know if thats the issue or not... the const iterator save is only used in the saveCargo function and has no issues. I have tried clean project, removing all references to const_iterator (and just used two QVector:: iterator calls) but so far no luck. If you need me to post additional code let me know.

[Lykurg]

the end() function is returning and iterater behind (= invalid) the vector. See inside the docs for "Container Classes" for a detailed explanation. So your app crashes since it is invalid. Dekrement the iterator and all should work fine.

[pheonixstorm]

Odd considering the same nearly the same code is in the addressbook tutorial

if (i == contacts.end()) {
        nameLine->clear();
        addressText->clear();
        return;
    }
 
    if (i == contacts.begin())
        i = contacts.end();
 
    i--;

if (i == contacts.end()) {
        nameLine->clear();
        addressText->clear();
        return;
    }

    if (i == contacts.begin())
        i = contacts.end();

    i--;

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Ok, nevermind.. I found the issue. Its not a bad iterator but bad iterator placement in the code. After looking at the above code segment I noticed MY placement of it-- was after calling for the information to post in the line edits. So should have read

it--;
ui->something->settext(it->variable)

it--;
ui->something->settext(it->variable)

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instead of

ui->something->settext(it->variable)
it--;

ui->something->settext(it->variable)
it--;

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Its always the stupid things you miss... Thanks for the info even though I didn't get a chance to read up on it before finding my blunder